At The Repair Bench
Chris Prioli, AD2CS
A Monthly Column Describing A Recent Repair Bench Event
WWW.AD2CS.COM
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Honorary Donation As Payment?
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A while back, in early February of this year, I received an e-mail from a Pitman resident who has a passing interest in ham and short-wave radio. I believe that he was sent to me by Jim Clark KA2OSV, but I am not one hundred percent sure about that. Anyway, his main SWL radio had developed a problem and was unusable for him. Now, he is an older shut-in gentleman whose only real contact with the wider world is via his short-wave listening hobby, so the SWL radio being inoperable was a big deal to him. |
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In his e-mail, he described the problem with the radio. It sounded fairly simple, so I told him that I would take a look at it for him. He had the radio dropped off to me by an ex-wife, and I went to work on it. The fix was relatively simple once I got the radio’s case open without doing any damage to it. What I needed to do was to re-secure the telescopic whip antenna to the RF input point in the circuit, and then re-mount the base of the antenna to its mounting boss inside the case. The whole repair, including tightening the antenna pivot point, putting a fresh set of batteries, in and testing the radio, probably took me ten minutes. I called him and told him that his radio was ready for pickup, and I did not charge him a penny for the job. His ex-wife again came to my house, this time to pick up the radio, which I had packaged up into its factory carton (he had sent the carton with the radio), just like a new radio.
He was quite happy to get his radio back, as it is his daily companion and window on the world. He called me and said that it worked like it did when it was brand new. The biggest visible difference, apart from the fact that the antenna was back where it belonged, is that the antenna no longer flopped around loosely. Because I had tightened the pivot point screw, the aerial now stayed where it was placed. I felt good about doing a favor for a senior citizen, and that was the end of it as far as I was concerned.
That was then… and I have not thought much about it since… until today, that is. You see, today I received a letter from the ARRL that relates to this repair. I am attaching a copy of the letter to this article for your reading pleasure, but the gist of it all is that he went and made a donation to the League in my honor, and the League was writing to tell me so.
It is funny how one random act of kindness turns into another act that reaches farther and impacts more people. I have no idea how much was donated, and it really does not matter. It is the thought process behind the donation that encourages me, and that is the reason that I am writing this… to share that encouragement.
Keep on doing good deeds. The good that we do is returned when we least expect it and often in ways that we would never have imagined. Read the letter below.
He was quite happy to get his radio back, as it is his daily companion and window on the world. He called me and said that it worked like it did when it was brand new. The biggest visible difference, apart from the fact that the antenna was back where it belonged, is that the antenna no longer flopped around loosely. Because I had tightened the pivot point screw, the aerial now stayed where it was placed. I felt good about doing a favor for a senior citizen, and that was the end of it as far as I was concerned.
That was then… and I have not thought much about it since… until today, that is. You see, today I received a letter from the ARRL that relates to this repair. I am attaching a copy of the letter to this article for your reading pleasure, but the gist of it all is that he went and made a donation to the League in my honor, and the League was writing to tell me so.
It is funny how one random act of kindness turns into another act that reaches farther and impacts more people. I have no idea how much was donated, and it really does not matter. It is the thought process behind the donation that encourages me, and that is the reason that I am writing this… to share that encouragement.
Keep on doing good deeds. The good that we do is returned when we least expect it and often in ways that we would never have imagined. Read the letter below.
Heathkit IM-5284 & IPA-5280-1 - October 2023
At this year’s GCARC Hamfest, I picked up a pair of items for a very low price - a Heathkit® IM-5824 multimeter and a Heathkit® IPA-5280-1 power supply for the 5280-series test instruments. I never checked at all to determine the condition of these items - the price was right regardless the condition, and I was confident that I could repair anything that may have been wrong with the two items. It turns out that I was not wrong, but the challenge ended up being quite considerable.
Let’s talk about condition first. The power supply was plugged in to the multimeter and could not be unplugged. It turned out that the -9VDC wire in the connector body had overheated and melted the connection together, leaving cutting the wires as the only means of removing the power supply from the multimeter. More about the power supply later.
The multimeter was a mess. This unit has two front-panel wafer-type rotary switches and two front panel potentiometers. All four of these controls were seized and would not turn at all. On the rear panel of the enclosure is the connector to which the power supply cable connects, which we already discussed, and also a slide switch that is used to select between the power supply as a power source and the internal battery bank as the power source. This switch was also seized and would not slide at all. When I opened up the enclosure, I found more damage. While the two nine-volt battery snaps were unpopulated, they were none the less severely corroded, beyond saving. There was a leaking “C” cell in the holder for the ohmmeter power source. The alkali from this cell had leaked all over the inside of the enclosure, coating the bottom of the enclosure and soaking into the paint on the front panel. Several wires had corroded off their attachment points, and the battery contacts for the “C” cell were corroded beyond use, with one of them actually broken into two pieces and the other corroded so badly that there were holes through the metal.
I began by completely disassembling the unit and starting the clean-up of the various pieces. That was when I discovered that the alkali had damaged the front panel paint to the point where the paint all the way across the lower edge of the front panel washed off when I rinsed the panel under cold running water. I cleaned the enclosure sections with warm water and dish soap, removing all traces of the alkali and the corrosion. I cleaned the front panel the same way. Fortunately, the damage to the paint remained below the portion of the panel where there were markings for the various controls, so it turned out to be an easy fix with a rattle-can of the right color paint, first masking out the lettering on the panel to avoid overspray damage there.
The rotary wafer switches required complete disassembly in order to free up the moving parts and to clean the wafers properly. I did this for both of the switches, restoring them to working condition. Next, I disassembled the two front panel potentiometers and cleaned and lubricated them in the same manner. DeoxIT is the best choice for cleaning and lubricating these components.
The next thing that I tackled was the rear panel slide switch, removing the original one and installing a new replacement switch in its place. Then I set about repairing the damaged wiring, including replacing the two nine-volt battery snap connectors. Once all of the damaged wiring was repaired, I had to fabricate two new battery contacts for the “C” cell position. This was done by cutting some 24-gauge copper sheet metal to the correct size, and then making two cuts in the bottom edge of each new contact, reaching up about three-quarters of the way to the top of each contact. The center strip, between the cuts, was bent forward to form a spring contact that projects forward from the plane of the contact. I soldered the contacts to their wire leads, and then slid them down into their proper locations in the “C” cell battery compartment.
Once the multimeter was fully assembled, I went through the calibration steps as detailed in the factory manual for this unit, successfully calibrating the multimeter. To complete the job, I made up a set of probe leads for the multimeter and put them into the storage compartment built into the upper enclosure half. Job done… and now it was time to turn to the power supply.
When tested, the power supply was dead. I opened it up and found that the fuse was blown. Digging deeper, I discovered that one of the full-wave rectifier diodes was shorted as was one of the 500µF filter capacitors. I replaced the failed diode and all of the polarized capacitors in the unit - two of the 500µF capacitors and a pair of 10µF capacitors at the outputs of the voltage regulator IC’s. I then replaced the fuse and tested the unit. It came right up and operated correctly, so I placed it under a load to verify the voltage regulation. The unit held rock steady at +9VDC and -9VDC at the two outputs. I assembled the power supply enclosure and replaced the cut-off plug that was melted when connected to the multimeter, and the power supply was as good as new.
Ultimately, I listed the two units on eBay, and the multimeter sold within two days at my full asking price. The power supply, as of this writing, is still available there.
It may seem like a reckless thing to do, to purchase some equipment on a whim without knowing anything about the condition of the equipment. It may actually be foolish. However, as I said earlier, I didn’t care what condition the items were in, as I was confident that I could restore them, and I did. Not only did I restore both items, I sold one of the two for considerably more than I paid for both of them together, and when the second item sells, as it will (it is a very rare piece of equipment), I will be that much further ahead. When you are sure of your abilities, and when you have the skills to overcome most problems, you can go out on a limb and take chances like this one was. And, when you are not so sure of your skills and abilities, there is no better way to learn and to build those skills than by trying.
Let’s talk about condition first. The power supply was plugged in to the multimeter and could not be unplugged. It turned out that the -9VDC wire in the connector body had overheated and melted the connection together, leaving cutting the wires as the only means of removing the power supply from the multimeter. More about the power supply later.
The multimeter was a mess. This unit has two front-panel wafer-type rotary switches and two front panel potentiometers. All four of these controls were seized and would not turn at all. On the rear panel of the enclosure is the connector to which the power supply cable connects, which we already discussed, and also a slide switch that is used to select between the power supply as a power source and the internal battery bank as the power source. This switch was also seized and would not slide at all. When I opened up the enclosure, I found more damage. While the two nine-volt battery snaps were unpopulated, they were none the less severely corroded, beyond saving. There was a leaking “C” cell in the holder for the ohmmeter power source. The alkali from this cell had leaked all over the inside of the enclosure, coating the bottom of the enclosure and soaking into the paint on the front panel. Several wires had corroded off their attachment points, and the battery contacts for the “C” cell were corroded beyond use, with one of them actually broken into two pieces and the other corroded so badly that there were holes through the metal.
I began by completely disassembling the unit and starting the clean-up of the various pieces. That was when I discovered that the alkali had damaged the front panel paint to the point where the paint all the way across the lower edge of the front panel washed off when I rinsed the panel under cold running water. I cleaned the enclosure sections with warm water and dish soap, removing all traces of the alkali and the corrosion. I cleaned the front panel the same way. Fortunately, the damage to the paint remained below the portion of the panel where there were markings for the various controls, so it turned out to be an easy fix with a rattle-can of the right color paint, first masking out the lettering on the panel to avoid overspray damage there.
The rotary wafer switches required complete disassembly in order to free up the moving parts and to clean the wafers properly. I did this for both of the switches, restoring them to working condition. Next, I disassembled the two front panel potentiometers and cleaned and lubricated them in the same manner. DeoxIT is the best choice for cleaning and lubricating these components.
The next thing that I tackled was the rear panel slide switch, removing the original one and installing a new replacement switch in its place. Then I set about repairing the damaged wiring, including replacing the two nine-volt battery snap connectors. Once all of the damaged wiring was repaired, I had to fabricate two new battery contacts for the “C” cell position. This was done by cutting some 24-gauge copper sheet metal to the correct size, and then making two cuts in the bottom edge of each new contact, reaching up about three-quarters of the way to the top of each contact. The center strip, between the cuts, was bent forward to form a spring contact that projects forward from the plane of the contact. I soldered the contacts to their wire leads, and then slid them down into their proper locations in the “C” cell battery compartment.
Once the multimeter was fully assembled, I went through the calibration steps as detailed in the factory manual for this unit, successfully calibrating the multimeter. To complete the job, I made up a set of probe leads for the multimeter and put them into the storage compartment built into the upper enclosure half. Job done… and now it was time to turn to the power supply.
When tested, the power supply was dead. I opened it up and found that the fuse was blown. Digging deeper, I discovered that one of the full-wave rectifier diodes was shorted as was one of the 500µF filter capacitors. I replaced the failed diode and all of the polarized capacitors in the unit - two of the 500µF capacitors and a pair of 10µF capacitors at the outputs of the voltage regulator IC’s. I then replaced the fuse and tested the unit. It came right up and operated correctly, so I placed it under a load to verify the voltage regulation. The unit held rock steady at +9VDC and -9VDC at the two outputs. I assembled the power supply enclosure and replaced the cut-off plug that was melted when connected to the multimeter, and the power supply was as good as new.
Ultimately, I listed the two units on eBay, and the multimeter sold within two days at my full asking price. The power supply, as of this writing, is still available there.
It may seem like a reckless thing to do, to purchase some equipment on a whim without knowing anything about the condition of the equipment. It may actually be foolish. However, as I said earlier, I didn’t care what condition the items were in, as I was confident that I could restore them, and I did. Not only did I restore both items, I sold one of the two for considerably more than I paid for both of them together, and when the second item sells, as it will (it is a very rare piece of equipment), I will be that much further ahead. When you are sure of your abilities, and when you have the skills to overcome most problems, you can go out on a limb and take chances like this one was. And, when you are not so sure of your skills and abilities, there is no better way to learn and to build those skills than by trying.
Heathkit IP-2718 Power Supply - September 2023
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Last month (in July 2023), I received an e-mail from a ham in Presque Isle, Maine, asking me if I would be interested in taking a look at an older Heathkit® IP-2718 Tri-Power Supply (Figure 1) that was not operating properly. I agreed to give it a shot, and had the owner ship the PSU to me. A rather compact power |
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supply that weighs in at a mere ten pounds, the IP-2718 is a three-output unit, having a 5VDC fixed output and a pair of identical 0V to 20VDC adjustable outputs. The two 20-volt outputs can be operated independently, or they can be set so that the “A” output tracks the “B” output. The 5VDC output is at 1500mA, while the 20VDC outputs are at 500mA each. The three outputs are all individually floating outputs which can be connected together in a wide variety of methods, whether in series, in parallel, or in any one of a number of series/parallel combinations. As a result, it is possible for example to achieve a developed output of -5VDC to -45VDC at a maximum output current of 500mA.
Figure 2 illustrates one of the many configurations possible. In this configuration, the +5V terminal is referenced to ground, and each of the 0 to +20V supplies are referenced to -5 volts. In this manner, each of the positive-going 20-volt supplies can be varied from -5VDC to +15VDC, or an overall span of 20 volts. Output currents for each of the three supplies are as shown in the Figure 2 diagram.
In another example, shown in Figure 3, we see the three outputs connected in series with the ground reference made at the high end of the series circuit string. In this circuit, the output voltage is adjustable from -5VDC to -45VDC, while the maximum output current is limited by the maximum current outputs of the “A” and “B” supplies to 500mA.
A third example can help to bring home the concept of multiple configurations yielding multiple outputs. In this example, shown at Figure 4, the supplies are connected in such a manner as to produce three separate outputs, a fixed +5VDC output at 0-1500mA current, the “A” 20-volt supply provides an output that is adjustable from 0V to +20VDC at 500mA, and the “B” 20-volt supply outputs an adjustable 0V to -20VDC also at 500mA.
Note that the polarity of these three outputs is dependent upon which terminal of each supply is connected to the green ground terminal. A careful look at Figure 4 will show that J2 and J4 - both negative terminals - are connected to ground, thus referencing those two supplies as positive-going outputs, but in the “B” supply, terminal J7 - a positive terminal - is connected to the ground point, thus referencing that output as a negative-going output.
Let’s take a look at yet another arrangement, in which we take the two 20-volt supplies out in parallel, thus allowing the currents of these two supplies to effectively add together, resulting in a nominal 1000mA output from the parallel pair. In Figure 5, we can see that a pair of current-sharing or equalizing resistors of 0.5Ω each is connected in series with each of the two 20-volt supplies’ positive terminals feeding the positive side of the load. The total output voltage is reduced by the voltage drops of these two resistors. The actual amount of those voltage drops will be determined by the spontaneous current draw of the circuit, as calculated via the Ohm’s Law formula of E = I x R. For example, if the circuit current draw is 946mA and if it were to be drawn exactly evenly from each of the two supplies (an unlikely circumstance), the voltage drop across each resistor would be (0.946/2) x 0.5, or 0.2365V. This would mean that the total voltage dropped across the two resistors would be 0.473V, or just under a half of a volt. That is the amount by which the total output voltage would be reduced in this configuration and at that specific current draw value. Of course, due to component tolerances and other related factors, the likelihood of having exactly half of the current provided by each of the 20-volt supplies is very slim, and is in fact almost impossible. However, the difference will be small enough that it should not have any meaningful impact on the circuit.
In one final example (Figure 6), we will look at the circumstance wherein we have one of the two 20-volt supplies tracking the other as to output voltage. In this particular power supply, the “A” output will track the “B” output when the unit is placed in the “TRACKING” mode. Under these conditions, each of the outputs is floating. However, almost any combination of series-connected outputs can be utilized in the tracking mode. The main take-away here is that the two 20-volt supply outputs need not be adjusted independently, as in this mode, whatever output voltage level the “B” supply is producing, the “A” supply will do the same.
OK - enough about how this supply is intended to operate. Now let’s talk about what it was not doing, or was doing improperly. To start with, the 5-volt supply exhibited heavy ripple and low output voltage. In addition, the 20-volt “A” supply had no output voltage at all, and the 20-volt “B” supply exhibited an output voltage that was too high and could not be adjusted to its proper value.
Under the cover here, there are three separate power supplies that are integrated within this unit. The 5-volt supply consists mainly of an LM309K three-pin voltage regulator IC, a pair of 1N5403 silicon diodes forming a full-wave rectifier, and a 12,000µF 15V aluminum electrolytic capacitor. In this case, diagnosis was easily accomplished because there was so little that could go wrong. As it turned out, the capacitor was extremely leaky, causing the ripple and also causing the failure of one of the two diodes in the full-wave rectifier. It was a no-brainer that both diodes should be replaced, as they were both placed under the same stresses. This portion of the IP-2718 is constructed with point-to-point wired components (Figure 7), so replacement was extremely simple. The 12,000µF capacitor (C2) has a 220Ω one-watt bleeder resistor placed across its terminals, the edge of which is just barely visible in the Figure 7 photo. The rear panel of the enclosure has a terminal tie strip on which are the two diodes of the full-wave rectifier. Replacement of the capacitor and the two diodes resolved the issues with the 5-volt supply. I did have to do a little bit of customization, as the replacement capacitor has screw terminals rather than the solder lugs of the original device. That was handled by putting solder lugs onto each of the leads that needed to go onto the capacitor, and then simply putting those lugs under the screws and tightening them down in place.
Next up was the 20-volt “A” supply, which had no output voltage. The two 20-volt supplies are identical in design, each occupying one half of the printed circuit board (PCB) on which they are installed. As a result of this happy circumstance, it is very easy to compare the two sections as to voltage readings at various points across the PCB. Component numbering here is laid out following the rule that all “one-hundred” series components are in the “A” supply section, while the “two-hundred” components are in the “B” supply section. Thus, for example, Q101 and Q201 are the same part number and serve the same function at the same location in each of the two supply sections.
The input to the 20-volt power supply is through a pair of 1N4002 silicon diodes configured as a full-wave rectifier directly off the secondary winding of the power transformer (Figure 8). The output of the full-wave rectifier, according to the schematic diagram, should be a nominal 37.6VDC.
At the anode of D103, which is the same point as the cathodes of D101 and D102, the point just referenced as the output of the full-wave rectifier, the actual voltage measured there was 0.030VDC, essentially no voltage. Voltage was present at the anodes of D101 and D102, and the voltage drop across each of those diodes was just over 36 volts. It was obvious that these diodes were both open, and therefore in need of replacement.
Due to the age of this unit, the number of electrolytic capacitors, the level of heat developed by the large power transformer, and the already verified failure of the 12,000µF filter capacitor C2, I decided to replace all of the electrolytic capacitors on the PCB. This equated to a total of twelve capacitors, six in each 20-volt section of the power supply.
I replaced all of those capacitors, installed the replacements for diodes D101 and D102, and then I checked the operation of the unit. The 20-volt “A” supply was restored to proper operation, but the “B” section was still not right. As mentioned earlier, this section exhibited an output that was too high and was not able to be adjusted to its proper level. Some more diagnosis was called for.
Mounted to the rear panel of the enclosure are three semiconductor devices. One of them is the LM309K voltage regulator IC already discussed. The other two are the pass transistors for the voltage regulator circuits of the 20-volt supplies. These transistors are of the type MJ2841 and are identified as Q1 (supply section “A”) and Q2 (supply section “B”). The MJ2841 transistor is a high-power NPN silicon transistor rated at 80VCEO, 80VCB, 4VEB, a collector current (IC) of 10A and a base current (IB) of 4A. The rated power dissipation is 150 watts and the device is in a TO-3 steel case. All told, this is a very sturdy and capable transistor, bordering on overkill for the job it is being asked to do in this power supply. The schematic (Figure 9) calls for an in-circuit operational base voltage of 20.1VDC, an emitter voltage of 20.0VDC, and a collector voltage of 36.7VDC. The emitter is directly connected to the J7 positive output jack for the 20-volt “B” supply and is therefore the supply output voltage. The collector voltage is one diode-drop, in this case 0.9V, less than the input voltage of 37.6V as mentioned in the section “A” discussion above. This is evident, as the only component in series between the D201 and D202 cathodes and the Q2 collector is a single 1N4002 silicon diode, D203.
The actual voltage measured at the emitter of Q2 and at the positive output terminal of the power supply “B” section was 36.9VDC, the same voltage as that found on the collector of Q2. From that information, it was evident that transistor Q2 was shorted, and thus merited replacement.
The type MJ2841 transistor is very difficult to find now, as it is an obsolete part. I found a couple of surplus houses that claimed to have inventory, and I even found a couple of eBay vendors offering the original part, but at extremely exorbitant pricing. The best price that I found was just over twenty dollars plus shipping, but I also found pricing as high as sixty dollars plus shipping. When it comes to replacement of some older semiconductor devices, a usually-viable alternative is NTE Electronics of Bloomfield, New Jersey. I have found suitable replacements in their product line-up before, and this time was no different. A look at my NTE QUICKCROSS™ software turned up the NTE-130 as a suitable replacement for the MJ2841. Amazon had it in stock for next-day delivery at just over five dollars. Sold!
When the transistor came in, I installed it and tested the operation of the IP-2718. It now worked properly on all three of its outputs. I gave the unit a quick cosmetic clean-up, inside and out, and buttoned it up for shipment back to its owner. Start to finish, I had the unit here for three days, shipping it out again on the third day after I received it. The quick turn-around time on this one was aided by the fact that I had all of the capacitors in stock, as well as the diodes. The only part that I needed to source and have shipped in was the pass transistor that we just discussed.
The group of electrolytic capacitors that I changed out on the main PCB included four (4) 10µF/50V axials, four (4) 50µF/50V axials, two (2) 50µF /15V radials (which I replaced with 47µF/63V radials), and two (2) 2,200µF/40V axials, which I replaced with 2,200µF/50V axial devices.
The moral of this story is that no matter how difficult a job may seem at the onset, break it down to its constituent parts and you may find that one difficult large job has become two or three easy smaller jobs. That is exactly what happened here.
See you next month!
Figure 2 illustrates one of the many configurations possible. In this configuration, the +5V terminal is referenced to ground, and each of the 0 to +20V supplies are referenced to -5 volts. In this manner, each of the positive-going 20-volt supplies can be varied from -5VDC to +15VDC, or an overall span of 20 volts. Output currents for each of the three supplies are as shown in the Figure 2 diagram.
In another example, shown in Figure 3, we see the three outputs connected in series with the ground reference made at the high end of the series circuit string. In this circuit, the output voltage is adjustable from -5VDC to -45VDC, while the maximum output current is limited by the maximum current outputs of the “A” and “B” supplies to 500mA.
A third example can help to bring home the concept of multiple configurations yielding multiple outputs. In this example, shown at Figure 4, the supplies are connected in such a manner as to produce three separate outputs, a fixed +5VDC output at 0-1500mA current, the “A” 20-volt supply provides an output that is adjustable from 0V to +20VDC at 500mA, and the “B” 20-volt supply outputs an adjustable 0V to -20VDC also at 500mA.
Note that the polarity of these three outputs is dependent upon which terminal of each supply is connected to the green ground terminal. A careful look at Figure 4 will show that J2 and J4 - both negative terminals - are connected to ground, thus referencing those two supplies as positive-going outputs, but in the “B” supply, terminal J7 - a positive terminal - is connected to the ground point, thus referencing that output as a negative-going output.
Let’s take a look at yet another arrangement, in which we take the two 20-volt supplies out in parallel, thus allowing the currents of these two supplies to effectively add together, resulting in a nominal 1000mA output from the parallel pair. In Figure 5, we can see that a pair of current-sharing or equalizing resistors of 0.5Ω each is connected in series with each of the two 20-volt supplies’ positive terminals feeding the positive side of the load. The total output voltage is reduced by the voltage drops of these two resistors. The actual amount of those voltage drops will be determined by the spontaneous current draw of the circuit, as calculated via the Ohm’s Law formula of E = I x R. For example, if the circuit current draw is 946mA and if it were to be drawn exactly evenly from each of the two supplies (an unlikely circumstance), the voltage drop across each resistor would be (0.946/2) x 0.5, or 0.2365V. This would mean that the total voltage dropped across the two resistors would be 0.473V, or just under a half of a volt. That is the amount by which the total output voltage would be reduced in this configuration and at that specific current draw value. Of course, due to component tolerances and other related factors, the likelihood of having exactly half of the current provided by each of the 20-volt supplies is very slim, and is in fact almost impossible. However, the difference will be small enough that it should not have any meaningful impact on the circuit.
In one final example (Figure 6), we will look at the circumstance wherein we have one of the two 20-volt supplies tracking the other as to output voltage. In this particular power supply, the “A” output will track the “B” output when the unit is placed in the “TRACKING” mode. Under these conditions, each of the outputs is floating. However, almost any combination of series-connected outputs can be utilized in the tracking mode. The main take-away here is that the two 20-volt supply outputs need not be adjusted independently, as in this mode, whatever output voltage level the “B” supply is producing, the “A” supply will do the same.
OK - enough about how this supply is intended to operate. Now let’s talk about what it was not doing, or was doing improperly. To start with, the 5-volt supply exhibited heavy ripple and low output voltage. In addition, the 20-volt “A” supply had no output voltage at all, and the 20-volt “B” supply exhibited an output voltage that was too high and could not be adjusted to its proper value.
Under the cover here, there are three separate power supplies that are integrated within this unit. The 5-volt supply consists mainly of an LM309K three-pin voltage regulator IC, a pair of 1N5403 silicon diodes forming a full-wave rectifier, and a 12,000µF 15V aluminum electrolytic capacitor. In this case, diagnosis was easily accomplished because there was so little that could go wrong. As it turned out, the capacitor was extremely leaky, causing the ripple and also causing the failure of one of the two diodes in the full-wave rectifier. It was a no-brainer that both diodes should be replaced, as they were both placed under the same stresses. This portion of the IP-2718 is constructed with point-to-point wired components (Figure 7), so replacement was extremely simple. The 12,000µF capacitor (C2) has a 220Ω one-watt bleeder resistor placed across its terminals, the edge of which is just barely visible in the Figure 7 photo. The rear panel of the enclosure has a terminal tie strip on which are the two diodes of the full-wave rectifier. Replacement of the capacitor and the two diodes resolved the issues with the 5-volt supply. I did have to do a little bit of customization, as the replacement capacitor has screw terminals rather than the solder lugs of the original device. That was handled by putting solder lugs onto each of the leads that needed to go onto the capacitor, and then simply putting those lugs under the screws and tightening them down in place.
Next up was the 20-volt “A” supply, which had no output voltage. The two 20-volt supplies are identical in design, each occupying one half of the printed circuit board (PCB) on which they are installed. As a result of this happy circumstance, it is very easy to compare the two sections as to voltage readings at various points across the PCB. Component numbering here is laid out following the rule that all “one-hundred” series components are in the “A” supply section, while the “two-hundred” components are in the “B” supply section. Thus, for example, Q101 and Q201 are the same part number and serve the same function at the same location in each of the two supply sections.
The input to the 20-volt power supply is through a pair of 1N4002 silicon diodes configured as a full-wave rectifier directly off the secondary winding of the power transformer (Figure 8). The output of the full-wave rectifier, according to the schematic diagram, should be a nominal 37.6VDC.
At the anode of D103, which is the same point as the cathodes of D101 and D102, the point just referenced as the output of the full-wave rectifier, the actual voltage measured there was 0.030VDC, essentially no voltage. Voltage was present at the anodes of D101 and D102, and the voltage drop across each of those diodes was just over 36 volts. It was obvious that these diodes were both open, and therefore in need of replacement.
Due to the age of this unit, the number of electrolytic capacitors, the level of heat developed by the large power transformer, and the already verified failure of the 12,000µF filter capacitor C2, I decided to replace all of the electrolytic capacitors on the PCB. This equated to a total of twelve capacitors, six in each 20-volt section of the power supply.
I replaced all of those capacitors, installed the replacements for diodes D101 and D102, and then I checked the operation of the unit. The 20-volt “A” supply was restored to proper operation, but the “B” section was still not right. As mentioned earlier, this section exhibited an output that was too high and was not able to be adjusted to its proper level. Some more diagnosis was called for.
Mounted to the rear panel of the enclosure are three semiconductor devices. One of them is the LM309K voltage regulator IC already discussed. The other two are the pass transistors for the voltage regulator circuits of the 20-volt supplies. These transistors are of the type MJ2841 and are identified as Q1 (supply section “A”) and Q2 (supply section “B”). The MJ2841 transistor is a high-power NPN silicon transistor rated at 80VCEO, 80VCB, 4VEB, a collector current (IC) of 10A and a base current (IB) of 4A. The rated power dissipation is 150 watts and the device is in a TO-3 steel case. All told, this is a very sturdy and capable transistor, bordering on overkill for the job it is being asked to do in this power supply. The schematic (Figure 9) calls for an in-circuit operational base voltage of 20.1VDC, an emitter voltage of 20.0VDC, and a collector voltage of 36.7VDC. The emitter is directly connected to the J7 positive output jack for the 20-volt “B” supply and is therefore the supply output voltage. The collector voltage is one diode-drop, in this case 0.9V, less than the input voltage of 37.6V as mentioned in the section “A” discussion above. This is evident, as the only component in series between the D201 and D202 cathodes and the Q2 collector is a single 1N4002 silicon diode, D203.
The actual voltage measured at the emitter of Q2 and at the positive output terminal of the power supply “B” section was 36.9VDC, the same voltage as that found on the collector of Q2. From that information, it was evident that transistor Q2 was shorted, and thus merited replacement.
The type MJ2841 transistor is very difficult to find now, as it is an obsolete part. I found a couple of surplus houses that claimed to have inventory, and I even found a couple of eBay vendors offering the original part, but at extremely exorbitant pricing. The best price that I found was just over twenty dollars plus shipping, but I also found pricing as high as sixty dollars plus shipping. When it comes to replacement of some older semiconductor devices, a usually-viable alternative is NTE Electronics of Bloomfield, New Jersey. I have found suitable replacements in their product line-up before, and this time was no different. A look at my NTE QUICKCROSS™ software turned up the NTE-130 as a suitable replacement for the MJ2841. Amazon had it in stock for next-day delivery at just over five dollars. Sold!
When the transistor came in, I installed it and tested the operation of the IP-2718. It now worked properly on all three of its outputs. I gave the unit a quick cosmetic clean-up, inside and out, and buttoned it up for shipment back to its owner. Start to finish, I had the unit here for three days, shipping it out again on the third day after I received it. The quick turn-around time on this one was aided by the fact that I had all of the capacitors in stock, as well as the diodes. The only part that I needed to source and have shipped in was the pass transistor that we just discussed.
The group of electrolytic capacitors that I changed out on the main PCB included four (4) 10µF/50V axials, four (4) 50µF/50V axials, two (2) 50µF /15V radials (which I replaced with 47µF/63V radials), and two (2) 2,200µF/40V axials, which I replaced with 2,200µF/50V axial devices.
The moral of this story is that no matter how difficult a job may seem at the onset, break it down to its constituent parts and you may find that one difficult large job has become two or three easy smaller jobs. That is exactly what happened here.
See you next month!
Victoreen Geiger Counter - August 2023
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A fellow club member recently brought some of the strangest repairs that I have seen so far… a pair of 1960’s vintage Geiger counters, neither of which was operational. The two devices were of different series, both of them Civil Defense standard survey units. One of them was a V-700 series unit while the other was a V-715 type.
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Geiger counters, back in those days, were put out to a common specification for the basic outward design and operational standards, but were built by the various firms that got involved inoutward design and operational standards, but were built by the various firms that got involved in the program each to its own design, electronically. This meant that any V-700 unit would look and function just the same as any other V-700 unit, regardless of the actual manufacturers, but under the skin, each maker had its own proprietary circuit design.
To make matters even more curious, certain manufacturers built multiple different models or design levels of specific devices. For example, from one manufacturer, there was a CD V-700 Model 6, Model 6A, and Model 6B. The circuits in these different design levels were not identical, with each successive sub-model having some sort of design advantage over its previous counterpart.
Of the units that were brought to me for repair, this article will discuss the Victoreen CD V-700 Model 6A Radiological Survey Meter. This unit is a two-transistor design that uses a Geiger tube as the sensing element, and originally used a corona discharge regulator tube in the high voltage power supply, which operated at about 900 volts. The unit is powered by four standard “D” cells as found in most flashlights at that time. The Geiger tube is mounted in a remote probe connected to the main unit via a thirty-six inch long cable. The probe is a nickel-plated brass tube with a window that can be opened to varying degrees to admit beta radiation. This unit will detect both beta and gamma radiation.
To make matters even more curious, certain manufacturers built multiple different models or design levels of specific devices. For example, from one manufacturer, there was a CD V-700 Model 6, Model 6A, and Model 6B. The circuits in these different design levels were not identical, with each successive sub-model having some sort of design advantage over its previous counterpart.
Of the units that were brought to me for repair, this article will discuss the Victoreen CD V-700 Model 6A Radiological Survey Meter. This unit is a two-transistor design that uses a Geiger tube as the sensing element, and originally used a corona discharge regulator tube in the high voltage power supply, which operated at about 900 volts. The unit is powered by four standard “D” cells as found in most flashlights at that time. The Geiger tube is mounted in a remote probe connected to the main unit via a thirty-six inch long cable. The probe is a nickel-plated brass tube with a window that can be opened to varying degrees to admit beta radiation. This unit will detect both beta and gamma radiation.
Figure 1 : PCB Before Repair
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Figure 2 : PCB After Repair
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The high voltage power supply, operating from about 850 to 920 volts, consists of an oscillator, a flyback transformer, a rectifier and a filter capacitor, as well as the 900V corona discharge regulator tube mentioned earlier. This power supply is operated from only two of the four “D” cells installed in the unit.
There is also a pulse shaping and metering circuit, supplied by the remaining two “D” cells, and using the second transistor for its oscillator. This circuit responds to output pulses from the Geiger tube, and forms amplified pulses that trigger the meter as well as the headphone circuit, where the characteristic “clicking” sound of the Geiger counter can be heard, as well as being seen on the meter.
The most apparent problem with this unit was the fact that both transistors had failed, as had the corona discharge tube. I was able to source a kit that contained all of the necessary parts including a Zener diode stack on a small PCB that replaced the corona discharge tube and now serves as the 900V regulator.
While the ceramic capacitors in this unit had not failed, I replaced them with their counterparts from the kit, as the replacements were rated for considerably higher voltages, some of which were operating at voltages very near their rated limits. The sole electrolytic capacitor exhibited severe leakage, with an ESR off the high end of the scale on my ESR meter. It too was in the repair kit, and was thus easily replaced.
The range switch was severely oxidized and required extensive cleaning and restoration. This was a job for the DeoxIT® G100L (DeoxIT Gold) cleaner and lubricant. A quarter-hour with some cotton swabs and the DeoxIT® did the trick, and the switch was restored to a fully operational condition. This might be a good point for a word or two about the DeoxIT® products that I use. I regularly use the DeoxIT® D5 cleaner and lubricant, which I purchase in an aerosol can. This is my everyday go-to product for switch and pot cleaning and restoration. I also use the DeoxIT® X10S Precision Instrument Lubricant for lubrication of such things as meter movements, tuning capacitor bearings and bushings, control shaft bushings, and so forth. However, when a really bad switch or pot shows up, I reach for the DeoxIT® G100L. This product is expensive (about $50 for a 25ml bottle), and as a result I use it only when I really need to, but when it is needed, there is no substitute! Sales talk ended…
A thorough cleaning of the contacts in the battery boxes, and a general cleaning of the exterior of the unit, and it was time for final assembly, testing, and calibration.
Testing consisted of measuring the operating voltages and comparing them to those provided on the unit schematic, which is found in the instruction manual. Next up was a check of the pulse shaping and integrating circuit using an oscilloscope. A three-volt square wave of 150 microseconds duration, followed by a -20V flyback pulse, is what we were looking for and what we found.
Calibration is accomplished simply enough, as a radioactive sample is mounted directly to the outside of the unit lower housing. The instruction manual, readily obtainable online, has calibration instructions that are well-written and easy to follow, so calibration was a breeze.
This unit turned out to be a relatively simple repair, and it was fun working on something that had a place in our national history during the Cold War era. I will write up the second unit, the CD V-715, in another article. That was a little bit different…
See you next month.
There is also a pulse shaping and metering circuit, supplied by the remaining two “D” cells, and using the second transistor for its oscillator. This circuit responds to output pulses from the Geiger tube, and forms amplified pulses that trigger the meter as well as the headphone circuit, where the characteristic “clicking” sound of the Geiger counter can be heard, as well as being seen on the meter.
The most apparent problem with this unit was the fact that both transistors had failed, as had the corona discharge tube. I was able to source a kit that contained all of the necessary parts including a Zener diode stack on a small PCB that replaced the corona discharge tube and now serves as the 900V regulator.
While the ceramic capacitors in this unit had not failed, I replaced them with their counterparts from the kit, as the replacements were rated for considerably higher voltages, some of which were operating at voltages very near their rated limits. The sole electrolytic capacitor exhibited severe leakage, with an ESR off the high end of the scale on my ESR meter. It too was in the repair kit, and was thus easily replaced.
The range switch was severely oxidized and required extensive cleaning and restoration. This was a job for the DeoxIT® G100L (DeoxIT Gold) cleaner and lubricant. A quarter-hour with some cotton swabs and the DeoxIT® did the trick, and the switch was restored to a fully operational condition. This might be a good point for a word or two about the DeoxIT® products that I use. I regularly use the DeoxIT® D5 cleaner and lubricant, which I purchase in an aerosol can. This is my everyday go-to product for switch and pot cleaning and restoration. I also use the DeoxIT® X10S Precision Instrument Lubricant for lubrication of such things as meter movements, tuning capacitor bearings and bushings, control shaft bushings, and so forth. However, when a really bad switch or pot shows up, I reach for the DeoxIT® G100L. This product is expensive (about $50 for a 25ml bottle), and as a result I use it only when I really need to, but when it is needed, there is no substitute! Sales talk ended…
A thorough cleaning of the contacts in the battery boxes, and a general cleaning of the exterior of the unit, and it was time for final assembly, testing, and calibration.
Testing consisted of measuring the operating voltages and comparing them to those provided on the unit schematic, which is found in the instruction manual. Next up was a check of the pulse shaping and integrating circuit using an oscilloscope. A three-volt square wave of 150 microseconds duration, followed by a -20V flyback pulse, is what we were looking for and what we found.
Calibration is accomplished simply enough, as a radioactive sample is mounted directly to the outside of the unit lower housing. The instruction manual, readily obtainable online, has calibration instructions that are well-written and easy to follow, so calibration was a breeze.
This unit turned out to be a relatively simple repair, and it was fun working on something that had a place in our national history during the Cold War era. I will write up the second unit, the CD V-715, in another article. That was a little bit different…
See you next month.
ICOM IC-3210 - July 2023
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This month’s repair tale involves an Icom IC-3210 dual-band mobile radio (Figure 1), which came in for two separate problems. First of all, the front panel backlighting was inoperative, making it almost impossible to read the display without the use of a flashlight. The second problem was that the radio would not lock in properly on the UHF band most of
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Figure 1 : IC-3210
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the time, though occasionally it would work normally. That problem is one of a type that is normally quite difficult to locate – an intermittent problem.
Figure 2 : Original Lamps With Boots
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Figure 3 : Logic PCB Foil Side With Lamp Holes Indicated
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Figure 4 : Logic PCB With Lamp Holes Indicated
The backlight problem was one that was to be expected with a radio of the age of this particular unit. The front panel on this model is backlit by a set of three T-1 12VDC incandescent lamps that are soldered in place on the front panel printed circuit board (PCB), called the logic board by Icom. Each of these lamps is covered with a yellow plastic boot (Figure 2) that provides the desired color to the illumination provided. The lamps sit down into holes in the PCB (Figure 3 & Figure 4) and have their wire leads soldered to pads on the PCB. The PCB holes index with recesses in the front panel carrier housing, directing the provided light into the rear area of the panel. All three of the lamps were burned out.
While replacements for the original lamps are readily available from standard component sources. I decided to replace them with LED’s instead, so as to preclude the probability of a repeat failure of the backlight system. In order to access the PCB and remove the failed lamps, the front panel subassembly must first be removed from the radio chassis, and then further disassembled. This involves removal of the steel frame and the plastic front cover, followed by removal of the three rotary controls. Finally, the LCD panel and its insulator can be removed by twisting the locking tabs to align them with the slots in the PCB. Once the tabs are aligned with the slots, the LCD panel can be pulled straight out from the PCB. After the LCD panel is removed, the plastic front panel carrier housing can be removed from the PCB by removing the small screws that secure the PCB to the carrier. Finally, some of the wiring harnesses can be gotten out of the way by unplugging them. As always, this is the time for some photos of the harness connections to be taken, against the future reconnection of these plugs to the main PCB.
Once the PCB is stripped down as far as is possible, removal of the lamps was a simple matter of heating their soldered lead connections and lifting the lamps out of their holes. I then cleaned the excess solder off the pads using a soldering iron and some flux-impregnated braided solder wick.
As mentioned above, I had decided to use LED’s instead of the OEM incandescent type of lamps for the replacements. I chose cool white LED’s in the 3mm (T-1) size, and I paired each LED with a 1kΩ resistor for current-limiting purposes. I removed the yellow plastic boots from the original lamps and installed them onto the LED’s. I then placed the LED’s in the lamp holes of the PCB, soldering the cathode leads to the appropriate pads. Next, I added a resistor to each of the LED anode leads, and then soldered the opposite end of the resistors to the appropriate PCB pads. Application of 12VDC from a power supply to the PCB showed that all three LED’s worked perfectly. It was time to move on to the other problem that the radio’s owner had reported.
Figure 5 : Tantalum Capacitors Removed
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Figure 6 : Locations Of Failed Capacitors
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I chose to tackle this problem while the front panel was still disassembled due to the fact that the most likely problem was the switch that is used to switch between bands. That switch is a 6mm x 6mm normally-open (NO) tactile pushbutton switch. When tested, the switch would make only when pressed very firmly. A normal pressing action on the switch would have no effect on the band selection. This one turned out to be a simple replacement of the switch. I desoldered the original switch, and installed the replacement, which I had on hand as it is a standard switch. Easy peasy, right? Not so much as you might think. It turned out that there was also a known problem with this radio model in that two capacitors on the main PCB are known to fail together with this switch. What happens is that two tantalum capacitors, C87 (0.22µF/35V) and C97 (4.7µF/35V) (Figure 5 & 6) have a tendency to fail with high leakage, causing the UHF phase-locked loop circuit to lose phase lock. The user causes the switch damage by repeatedly working the switch, often aggressively, in an attempt to get the radio to lock onto the UHF band. This action causes the switch to become fatigued internally, leading to the switch failure found on this unit. As a result, the switch merited replacement, as did the two tantalum capacitors. On testing of the removed capacitors, they both had extremely high DC leakage values, and had ESR readings of 14.6Ω for C97 and 9.3Ω for C87.
I next checked the memory keep-alive battery, a BR-2032 coin cell. Yes, that is correct and not a typographical error. It turns out that the BR-series of coin cells are designed for low current drain over an extended period of time. Whereas I had CR-2032 cells in stock with the right welded tabs, I did not want to change the life expectancy of the coin cell in the radio by installing a CR-2032 cell.
The radio dates back to the late 1980’s - its production was discontinued in 1990. The cell in place in the radio had the Icom part number on it, so it was either an original part or a replacement installed by an authorized service center (or someone who bought the cell from Icom). While it is possible that this was the factory cell, it is equally unlikely that it was still original after all of these intervening years. I disconnected it from the circuit for testing, and found that the open-circuit voltage was reading right about 3 volts (3.04V to be exact), which is the nominal voltage of the cell. However, when tested under load, the voltage dropped down to just over 1 volt (1.156V to be exact). Load testing of these cells is best done by installing a 100Ω resistor between the voltmeter leads when measuring the cell voltage. The resistor provides the requisite load, which really tells the story.
I keep a couple of resistors of different values, soldered between small alligator clips, on hand for just this purpose. To use them, I simply select the one with the load value that I want to use, and connect the alligator clips to the voltmeter probes. Then, whenever I measure a battery or cell with the voltmeter with the resistor clipped in place, it is automatically providing a load test for the battery or cell. You can develop a list of desired resistor values for this task by perusing the various battery or cell datasheets. The datasheet will usually provide testing information which includes the load placed on the DUT during testing.
Anyway, I ordered in the correct BR-2032 with the necessary welded tabs for this application, and when it came in, I installed it. However, I did do a load test on the new cell before installation. This one started out at 3.49V open circuit, and only dropped to 3.15V under the 100Ω load test.
After the installation of the coin cell, it was time to re-assemble the radio. Re-assembly went without a hitch, with the only point of note being that the contact fingers along the edge of the PCB where the rubberized contact pad for the LCD panel mates with the PCB need to be clean. I scrubbed them with a pencil eraser, and then removed any skin oil using 99% isopropyl alcohol (IPA) on a cotton swab. This provides for trouble-free connection to the LCD panel after handling the PCB as much as I had done. If you had inadvertently touched the business edge of the rubberized contact pad, that too should be cleaned of skin oil with some 99% IPA on a cotton swab.
Assembly is otherwise the reverse of the disassembly operation. Take care to properly tighten the control nuts on the three rotary controls, and to tighten the PCB to plastic carrier screws without overtightening and stripping them. A quick word about screwdrivers, which maybe should have been mentioned earlier. This radio was manufactured in Japan and therefore uses JIS screws throughout. As a result, JIS screwdrivers are needed to loosen any tight screws without stripping the drive recess in the screw head. Standard Phillips screwdrivers or any variation thereof will certainly cause damage to the screw heads. During disassembly, I found that one of the screws that secured the shield plate and the front panel metal frame to the radio chassis had been stripped in that manner, telling me that someone had been into this radio before and most likely had not realized at first that the screws were JIS screws. I used a specialized extractor to remove the screw, and I replaced that screw upon reassembly with a new JIS 3mm-0.5mm x 6mm flat head machine screw from my inventory.
Remember that in screw dimensioning, the first part (before the hyphen) is the nominal thread diameter, while the second part (after the hyphen) is the thread pitch reference (more about that later). The number after the “x” is the fastener length. Metric fasteners and Imperial fasteners utilize different thread pitch designation methods. With a metric threaded fastener, the pitch information is reported as the distance from the peak of one thread to the peak of the adjacent thread. Thus, a machine screw with a pitch designation of 0.5mm will have a measured distance of one-half of a millimeter from one thread peak to the next. Imperial fasteners use a system that reports the number of thread peaks in an inch of fastener length. Thus, a machine screw with a pitch designation of 32 will have 32 thread peaks in an inch of screw length. Keep in mind also that while most headed fasteners are length-measured from the underside of the head, flat-head fasteners are length-measured for overall length, including the head length.
Reconnecting of the various wire harness plugs to the main PCB is pretty much a straight-forward matter of matching the plug size to the socket size. The is only one possible mix-up, and that is with the squelch control harness plug and the speaker harness plug. This can be resolved easily if the photos recommended earlier were taken. If not, refer to the schematic diagram found in the IC-3210 service manual to determine that the squelch control harness plug goes to connector J6 on the main PCB, while the speaker harness plug goes to connector J9.
Once the reassembly is complete, it is time for a functional test of the repairs. As luck would have it, another problem became evident quite quickly. It turned out that the rotary control used as the main up/down control signal source was inoperative. As a result, frequency could not be adjusted within each band, although the radio was otherwise fully functional on each of its two bands. In a similar manner, none of the radio’s optional settings that require an up/down selection normally made via that control were operational. Thus, the tuning step intervals, the CTCSS tones, and several other functions could not be changed. The problem gets worse… it turns out that the microphone Up/Down controls were also inoperable. This would seem to point to some circuit or component that is common to both control methods. In this case, I worked through the block diagram, the unit schematic, and the X-Ray views of the printed circuit boards in an effort to try to isolate the cause of this problem. Unfortunately, all of this testing and probing led to the inescapable conclusion that the problem lies within the logic board CPU integrated circuit, a µPD75308GF-101-3B9 device that is no longer available. So… while the relatively minor faults for which the radio came in were all corrected, the radio is nonetheless still inoperable, as the VFO frequencies cannot be changed. When powered on, the radio comes up on the designated calling frequencies of 146.520 MHz for VHF and 446.000 MHz for UHF.
Continued testing showed that one of the four output strobe lines from the CPU to the control matrices was extremely low in voltage as compared to the other three strobe lines, though its signal waveform was of the correct shape - just lower in amplitude than it should have been. I also noted that when exercising any of the switches on that particular strobe line, there was no response in the CPU, as those lines were not brought to a deep low with the switch activation - they were already low, so the CPU did not see the switch activations as changes of state on those lines. Unfortunately, no ready repair was available for this problem, as the CPU integrated circuit is obsolete and is therefore currently unavailable.
Sometimes, due to the so-called “planned obsolescence” so prevalent in the output of many of today’s manufacturing plants, an otherwise great little dual-band radio is relegated to the junk pile. I will keep my eyes and ears open on the lookout for another IC-3210 that I can pick up for parts, but I imagine that to be a rather futile effort. There are surprisingly few hits on Google when searching for that model number. I cannot in good conscience charge this radio owner a penny for my time spent and for the repairs that were made, as the end result was not a working radio.
See you next month!
I next checked the memory keep-alive battery, a BR-2032 coin cell. Yes, that is correct and not a typographical error. It turns out that the BR-series of coin cells are designed for low current drain over an extended period of time. Whereas I had CR-2032 cells in stock with the right welded tabs, I did not want to change the life expectancy of the coin cell in the radio by installing a CR-2032 cell.
The radio dates back to the late 1980’s - its production was discontinued in 1990. The cell in place in the radio had the Icom part number on it, so it was either an original part or a replacement installed by an authorized service center (or someone who bought the cell from Icom). While it is possible that this was the factory cell, it is equally unlikely that it was still original after all of these intervening years. I disconnected it from the circuit for testing, and found that the open-circuit voltage was reading right about 3 volts (3.04V to be exact), which is the nominal voltage of the cell. However, when tested under load, the voltage dropped down to just over 1 volt (1.156V to be exact). Load testing of these cells is best done by installing a 100Ω resistor between the voltmeter leads when measuring the cell voltage. The resistor provides the requisite load, which really tells the story.
I keep a couple of resistors of different values, soldered between small alligator clips, on hand for just this purpose. To use them, I simply select the one with the load value that I want to use, and connect the alligator clips to the voltmeter probes. Then, whenever I measure a battery or cell with the voltmeter with the resistor clipped in place, it is automatically providing a load test for the battery or cell. You can develop a list of desired resistor values for this task by perusing the various battery or cell datasheets. The datasheet will usually provide testing information which includes the load placed on the DUT during testing.
Anyway, I ordered in the correct BR-2032 with the necessary welded tabs for this application, and when it came in, I installed it. However, I did do a load test on the new cell before installation. This one started out at 3.49V open circuit, and only dropped to 3.15V under the 100Ω load test.
After the installation of the coin cell, it was time to re-assemble the radio. Re-assembly went without a hitch, with the only point of note being that the contact fingers along the edge of the PCB where the rubberized contact pad for the LCD panel mates with the PCB need to be clean. I scrubbed them with a pencil eraser, and then removed any skin oil using 99% isopropyl alcohol (IPA) on a cotton swab. This provides for trouble-free connection to the LCD panel after handling the PCB as much as I had done. If you had inadvertently touched the business edge of the rubberized contact pad, that too should be cleaned of skin oil with some 99% IPA on a cotton swab.
Assembly is otherwise the reverse of the disassembly operation. Take care to properly tighten the control nuts on the three rotary controls, and to tighten the PCB to plastic carrier screws without overtightening and stripping them. A quick word about screwdrivers, which maybe should have been mentioned earlier. This radio was manufactured in Japan and therefore uses JIS screws throughout. As a result, JIS screwdrivers are needed to loosen any tight screws without stripping the drive recess in the screw head. Standard Phillips screwdrivers or any variation thereof will certainly cause damage to the screw heads. During disassembly, I found that one of the screws that secured the shield plate and the front panel metal frame to the radio chassis had been stripped in that manner, telling me that someone had been into this radio before and most likely had not realized at first that the screws were JIS screws. I used a specialized extractor to remove the screw, and I replaced that screw upon reassembly with a new JIS 3mm-0.5mm x 6mm flat head machine screw from my inventory.
Remember that in screw dimensioning, the first part (before the hyphen) is the nominal thread diameter, while the second part (after the hyphen) is the thread pitch reference (more about that later). The number after the “x” is the fastener length. Metric fasteners and Imperial fasteners utilize different thread pitch designation methods. With a metric threaded fastener, the pitch information is reported as the distance from the peak of one thread to the peak of the adjacent thread. Thus, a machine screw with a pitch designation of 0.5mm will have a measured distance of one-half of a millimeter from one thread peak to the next. Imperial fasteners use a system that reports the number of thread peaks in an inch of fastener length. Thus, a machine screw with a pitch designation of 32 will have 32 thread peaks in an inch of screw length. Keep in mind also that while most headed fasteners are length-measured from the underside of the head, flat-head fasteners are length-measured for overall length, including the head length.
Reconnecting of the various wire harness plugs to the main PCB is pretty much a straight-forward matter of matching the plug size to the socket size. The is only one possible mix-up, and that is with the squelch control harness plug and the speaker harness plug. This can be resolved easily if the photos recommended earlier were taken. If not, refer to the schematic diagram found in the IC-3210 service manual to determine that the squelch control harness plug goes to connector J6 on the main PCB, while the speaker harness plug goes to connector J9.
Once the reassembly is complete, it is time for a functional test of the repairs. As luck would have it, another problem became evident quite quickly. It turned out that the rotary control used as the main up/down control signal source was inoperative. As a result, frequency could not be adjusted within each band, although the radio was otherwise fully functional on each of its two bands. In a similar manner, none of the radio’s optional settings that require an up/down selection normally made via that control were operational. Thus, the tuning step intervals, the CTCSS tones, and several other functions could not be changed. The problem gets worse… it turns out that the microphone Up/Down controls were also inoperable. This would seem to point to some circuit or component that is common to both control methods. In this case, I worked through the block diagram, the unit schematic, and the X-Ray views of the printed circuit boards in an effort to try to isolate the cause of this problem. Unfortunately, all of this testing and probing led to the inescapable conclusion that the problem lies within the logic board CPU integrated circuit, a µPD75308GF-101-3B9 device that is no longer available. So… while the relatively minor faults for which the radio came in were all corrected, the radio is nonetheless still inoperable, as the VFO frequencies cannot be changed. When powered on, the radio comes up on the designated calling frequencies of 146.520 MHz for VHF and 446.000 MHz for UHF.
Continued testing showed that one of the four output strobe lines from the CPU to the control matrices was extremely low in voltage as compared to the other three strobe lines, though its signal waveform was of the correct shape - just lower in amplitude than it should have been. I also noted that when exercising any of the switches on that particular strobe line, there was no response in the CPU, as those lines were not brought to a deep low with the switch activation - they were already low, so the CPU did not see the switch activations as changes of state on those lines. Unfortunately, no ready repair was available for this problem, as the CPU integrated circuit is obsolete and is therefore currently unavailable.
Sometimes, due to the so-called “planned obsolescence” so prevalent in the output of many of today’s manufacturing plants, an otherwise great little dual-band radio is relegated to the junk pile. I will keep my eyes and ears open on the lookout for another IC-3210 that I can pick up for parts, but I imagine that to be a rather futile effort. There are surprisingly few hits on Google when searching for that model number. I cannot in good conscience charge this radio owner a penny for my time spent and for the repairs that were made, as the end result was not a working radio.
See you next month!
NanoVNA H4 Touch Screen - June 2023
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One recent Saturday afternoon, one of our fellow Club members had cause to use the Club’s NanoVNA for some new equipment testing. Unfortunately, when he tried to operate the unit, the touch-screen feature was not working, and in fact, it seemed that the menu system was completely inoperative. I decided to bring it home with me to make the required repairs.
The Club’s NanoVNA is the H4 (Figure 1) variant which, at the time, was loaded with the DiSlord version 1.1.01 firmware dated 30 December 2021. While the firmware was most |
Figure 1 : NanoVNA H4
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likely not the cause of the problem, as the unit had been working fine for a long while, I did notice that the firmware was about a year and a half old, which is a lifetime by today’s electronic equipment standards. I slated it for a firmware update as a part of the repair.
In testing the NanoVNA quite thoroughly, I found that occasionally, I could get the menu system to operate via the multi-function control (MFC) wheel on the unit’s top edge, after which the touch screen would occasionally operate until the next power-off. However, it was not consistent enough to say that this would be a usable work-around, so I kept on digging for an answer.
I opened up the unit and disconnected the battery and the touch screen ribbon cable. I then reseated the ribbon cable, reconnected the battery, and powered up the device. No change was evident, with the touch screen and menu system operating the same as it had before the disconnects.
A few more words about the actual behavior would seem appropriate at this point. If I was able to get the menu system to launch using the MFC wheel, it was then possible to navigate the menu using the stylus via the touch screen. It was even possible to re-launch the menu system via the touch screen, until the unit was powered off. Then the problem re-asserted itself and it was pot luck as to whether or not the menus would open via the MFC.
I turned to that giant reference resource called the internet for some help, and I came across an obscure reference in a forum somewhere - I never noticed where - that made mention of NanoVNA stability. This seemed to fit, so I looked some more into that concept - stability and how to control it. What I found was that the default settings for the DiSlord firmware versions are set to slightly over-clock the NanoVNA. I decided to slow it down a little bit and see what happens.
The clock speed of the NanoVNA is controlled by a firmware value called Threshold, which is set to 300.000100MHz by default. The Threshold setting (Figure 2) is found under Config > Expert Settings. I decided to set it down to 290MHz. Voilá! The touch screen now behaved normally in every regard! I figured that I had resolved this issue, though I still did not understand what had happened, or specifically why it spontaneously stopped working after operating for so long, but I chose not to worry about that at this point.
In testing the NanoVNA quite thoroughly, I found that occasionally, I could get the menu system to operate via the multi-function control (MFC) wheel on the unit’s top edge, after which the touch screen would occasionally operate until the next power-off. However, it was not consistent enough to say that this would be a usable work-around, so I kept on digging for an answer.
I opened up the unit and disconnected the battery and the touch screen ribbon cable. I then reseated the ribbon cable, reconnected the battery, and powered up the device. No change was evident, with the touch screen and menu system operating the same as it had before the disconnects.
A few more words about the actual behavior would seem appropriate at this point. If I was able to get the menu system to launch using the MFC wheel, it was then possible to navigate the menu using the stylus via the touch screen. It was even possible to re-launch the menu system via the touch screen, until the unit was powered off. Then the problem re-asserted itself and it was pot luck as to whether or not the menus would open via the MFC.
I turned to that giant reference resource called the internet for some help, and I came across an obscure reference in a forum somewhere - I never noticed where - that made mention of NanoVNA stability. This seemed to fit, so I looked some more into that concept - stability and how to control it. What I found was that the default settings for the DiSlord firmware versions are set to slightly over-clock the NanoVNA. I decided to slow it down a little bit and see what happens.
The clock speed of the NanoVNA is controlled by a firmware value called Threshold, which is set to 300.000100MHz by default. The Threshold setting (Figure 2) is found under Config > Expert Settings. I decided to set it down to 290MHz. Voilá! The touch screen now behaved normally in every regard! I figured that I had resolved this issue, though I still did not understand what had happened, or specifically why it spontaneously stopped working after operating for so long, but I chose not to worry about that at this point.
I next went about performing a firmware upgrade on the NanoVNA. This is a simple operation that is done using the STMicroelectronics DfuSe software. I had the software (Figure 3) installed on my PC already, so all that I needed to do was to download the newest DiSlord firmware file in the commonly-used .dfu firmware format. That filename is NanoVNA.H4.v1.2.20.dfu which indicates that the firmware is version 1.2.20, dated 12 March 2023. The various firmware files can be downloaded from https://github.com/DiSlord/NanoVNA-D/releases under the Assets listing.
To update the firmware in the NanoVNA, the device must be placed into DFU mode. Start out by launching the STMicro DfuSe software and connecting the NanoVNA to the PC via an appropriate USB cable. Then, put the NanoVNA into DFU mode by holding down the MFC wheel while powering up the unit. Note that the screen will remain black in DFU mode, but the STMicro DfuSe software should indicate that the NanoVNA is connected and accessible. The net step is to use the Choose button in the DfuSe software to open the .dfu firmware file. The software will show (Figure 4) that the firmware file was successfully loaded into the utility and that it is ready for upload to the device. Upload that file to the device by clicking the Upgrade button. Once the upgrade is completed as indicated in the software (Figure 5), power off the NanoVNA and disconnect it from the PC.
The interesting thing about this repair is that post-upgrade of the firmware, that new firmware Threshold setting was once again set to 300.000100MHz… but the unit was operating properly and with many more menu options than it had before.
OK - so slowing the clock speed solved the initial touch screen response issue in the old firmware. Of that there is no doubt. As a result, I feel comfortable suggesting that as a solution for anyone who may encounter a similar issue with the touch screen on a NanoVNA H4 and needs an immediate fix.
I also feel comfortable recommending the firmware upgrade to DiSlord version 1.2.20, as I have now installed and tested it extensively, and everything works as it should. Some of the new features include the ability to save a calibration set to the SD card, enter a custom name for any image file saved to the SD card (or simply check the Autoname check box to avoid having to enter a name - it will default to a date and time format naming convention). The new firmware allows loading an image from the SD card into the display, and there is also a Pause Sweep and Resume Sweep capability now. There are several changes to the Calibrate menu item as well as to several other menu items. This new firmware version is feature-rich and is well worth installing.
Having explored the new menu items and capabilities of the NanoVNA H4 under DiSlord firmware 1.2.20, I am happy to report that all of the new features work well, and are for the most part self-explanatory or very intuitive. This makes these new features easy to use without needing any type of documentation for them. I like the new firmware so much that I also installed it onto my personal H4 unit.
See you next month…
To update the firmware in the NanoVNA, the device must be placed into DFU mode. Start out by launching the STMicro DfuSe software and connecting the NanoVNA to the PC via an appropriate USB cable. Then, put the NanoVNA into DFU mode by holding down the MFC wheel while powering up the unit. Note that the screen will remain black in DFU mode, but the STMicro DfuSe software should indicate that the NanoVNA is connected and accessible. The net step is to use the Choose button in the DfuSe software to open the .dfu firmware file. The software will show (Figure 4) that the firmware file was successfully loaded into the utility and that it is ready for upload to the device. Upload that file to the device by clicking the Upgrade button. Once the upgrade is completed as indicated in the software (Figure 5), power off the NanoVNA and disconnect it from the PC.
The interesting thing about this repair is that post-upgrade of the firmware, that new firmware Threshold setting was once again set to 300.000100MHz… but the unit was operating properly and with many more menu options than it had before.
OK - so slowing the clock speed solved the initial touch screen response issue in the old firmware. Of that there is no doubt. As a result, I feel comfortable suggesting that as a solution for anyone who may encounter a similar issue with the touch screen on a NanoVNA H4 and needs an immediate fix.
I also feel comfortable recommending the firmware upgrade to DiSlord version 1.2.20, as I have now installed and tested it extensively, and everything works as it should. Some of the new features include the ability to save a calibration set to the SD card, enter a custom name for any image file saved to the SD card (or simply check the Autoname check box to avoid having to enter a name - it will default to a date and time format naming convention). The new firmware allows loading an image from the SD card into the display, and there is also a Pause Sweep and Resume Sweep capability now. There are several changes to the Calibrate menu item as well as to several other menu items. This new firmware version is feature-rich and is well worth installing.
Having explored the new menu items and capabilities of the NanoVNA H4 under DiSlord firmware 1.2.20, I am happy to report that all of the new features work well, and are for the most part self-explanatory or very intuitive. This makes these new features easy to use without needing any type of documentation for them. I like the new firmware so much that I also installed it onto my personal H4 unit.
See you next month…
Brother P-Touch® 1400 Label Printer – May 2023
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Fairly recently, I was presented with a somewhat different type of repair. One of my fellow radio Club members asked me if I would take a look at a favorite and trusted piece of his shack equipment, namely a Brother P-touch® 1400 hand-held label printer (Figure 1). The printer had stopped responding to the “Y” key, and its owner was hoping that I could repair the machine for him. Enjoying a challenge, I told him that I would take it on, but without any up-front guarantee of success.
The owner brought the machine to me, and I quickly determined that not only did the “Y” key not work at all, the other keys along the right edge of the keyboard were rather “mushy” and not crisp and quick as they should have been. I opened up the unit to find that the printed circuit board on which the key contacts were etched had delaminated at a mounting pad along its right-hand edge, directly in alignment with the “Y” key, and breaking the circuit traces for that key and one other. This was apparently a product of years of use and pressure on that portion of the board. The keyboard consists of a matrix of conductive pads etched onto the top surface of a phenolic board that also serves as a printed circuit board for some of the related circuitry. Each key |
Figure 1 : Brother P-touch 1400
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contains a carbon button on its underside that bridges the conductive pads when the key is pressed. Simple enough, right? The problem was that the board had split between its layers (Figure 2), tearing the circuit traces on its upper surface. I was faced with a dual problem – how to first repair the delaminated phenolic board, and then how to repair the circuit traces (Figure 3) so that the machine would operate properly afterwards.
The first problem was solved with some cyanoacrylate glue, applied between the layers, with the layers then being clamped together with the broken section positioned back where it belonged. I clamped it up and set it aside to cure, having placed some waxed paper between the clamp faces and the board surfaces so that the clamp would not end up glued to the board by the excess glue squeeze-out. I then started thinking about the most effective manner in which to repair the circuit traces, assuming that the glue job would hold, of which I was not certain yet.
The most common method of repairing lifted or broken printed circuit traces, by far, is to simply scrape the trace to expose the conductive surface, and then to overlay the trace with some bare wire, and to then solder the wire to the trace. While this might work in some cases, it would clearly not be an effective repair in this situation, as one broken trace was directly in the area where the “Y” key’s carbon button would have to make contact with the board if that key were to be pressed. Any raised area of the board would be problematic in allowing the carbon button to successfully bridge the pads, which actually contain interlaced “fingers” (Figure 4) rather than being geometrically shaped areas. I needed a better solution.
The first problem was solved with some cyanoacrylate glue, applied between the layers, with the layers then being clamped together with the broken section positioned back where it belonged. I clamped it up and set it aside to cure, having placed some waxed paper between the clamp faces and the board surfaces so that the clamp would not end up glued to the board by the excess glue squeeze-out. I then started thinking about the most effective manner in which to repair the circuit traces, assuming that the glue job would hold, of which I was not certain yet.
The most common method of repairing lifted or broken printed circuit traces, by far, is to simply scrape the trace to expose the conductive surface, and then to overlay the trace with some bare wire, and to then solder the wire to the trace. While this might work in some cases, it would clearly not be an effective repair in this situation, as one broken trace was directly in the area where the “Y” key’s carbon button would have to make contact with the board if that key were to be pressed. Any raised area of the board would be problematic in allowing the carbon button to successfully bridge the pads, which actually contain interlaced “fingers” (Figure 4) rather than being geometrically shaped areas. I needed a better solution.
The next day, still unsure of how to repair the traces, I removed the clamp and waxed paper to find that the board was indeed back into a semblance of its original condition. I used some acetone on a cotton swab to clean the squeezed-out CA glue from the board surface in the area of concern, and the board was ready for trace repairs to begin. Still not having a repair scheme in mind, I put it aside for the day and moved on to something else, having already sent photos of the damage to the machine’s owner and having told him that a repair might not be feasible. I went to bed that night thinking about the problem.
At some point during the night, and driven by some unknown and not understood “force”, I hit upon an idea that might just work. I had read a while back about pens that write with conductive ink, which contains powdered silver in a volatile carrier. It was well worth a try, so I ordered one of the pens from Amazon and waited another day for it to arrive. Lo and behold, when I tried the pen on some paper, and then measured the resistance of the drawn lines, I found them to be very low impedance traces, and with almost no appreciable height on the paper surface.
I tried some basic experiments to determine the current-carrying capability of the ink, and found that I could easily pass 500mA through a trace that was two pen-points in width. This looked very promising indeed! I decided to try the ink on the phenolic board.
To make this idea work, I would have to expose some of the conductive surface of the existing traces for the ink to connect into the original circuit properly. That was a chore best done with the edge of a hobby knife blade, and that is exactly how I achieved the exposure that I needed. I then laid the ink down in place (Figure 5) over the almost invisible cracks in the repaired surface of the board, and checked the results with an ohmmeter. So far, do good. Now for the acid test. Will the key work when coming into contact with the ink and the original traces? A quick test with the keyboard membrane laid over the board proved that it would actually work as intended.
After that, all that was required was to reassemble the machine with the repaired PCB (Figure 6) and to do a final working test of the entire keyboard. That post-assembly test proved successful, and so the repair was complete. The lessons found in this repair are two-fold.
First, think out of the box when faced with an unusual problem, as unusual problems often require unusual repair methods.
Second, do not give up too easily. Plan for the worst, but work towards the best, and let your unconscious mind work on the problem for a while.
You might just know how to achieve a repair, even if you don’t know that you know how to do it!
See you next month.
Icom ID-800H – April 2023
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Sometimes, finding the cause of a problem can be more than the repair technician is up to. At those times, the technician has to be careful not to do any harm to the equipment and cause further failures while trying to ferret out the root cause of the initial failure. Sometimes, like the infamous Zorro, the technician leaves his/her mark in the night, gives up, and moves on. That is when the failure becomes another technician’s problem to solve.
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A little while ago, I got an email from a ham out in Cleveland, Tennessee who asked if I would be willing and able to take on a “mystery” repair on an Icom ID-800H 2-meter/70-centimeter dual-band mobile radio (Figure 1). The unit had an intermittent fault that two other shops had attempted to repair and both gave up without finding the problem. In addition, one of the two shops caused an additional failure, which we will get into in a little while.
The original problem was related to the occasional and unpredictable blown fuse on the incoming power line. The ID-800H was vehicle-mounted in a 2022 Peterbilt 579 (Figure 2) Class 8 truck-tractor. The secondary problem was a lack of audio from the radio unless an external speaker was installed and connected. This problem showed up when the radio came back from the second repair shop. The owner is an over-the-road long-distance trucker who has historically had his radio - CB’s and ham - all repaired at truck stop radio shops.
When the problem first appeared, the owner took the radio to a radio shop at a truck stop in Carlisle, PA. Of course, as nothing was actually repaired other than replacement of the blown fuse, the problem eventually re-occurred. At this point, the owner replaced the fuse himself, and the radio worked as it was intended to, for a while. At some point, the owner happened to have some time to kill while in Kenly, NC, so he took the radio to a radio shop at a truck stop there. This time when he reinstalled it in the truck, it worked again, except that there was no audio from the internal speaker. This was annoying, and the owner assumed that the repairman simply forgot to reconnect the speaker wire harness to the mainboard on re-assembly. However, due to the ambient noise level in the truck, he customarily used an amplified external speaker anyway, so he didn’t fret too much about it. Needless to say, the radio was still blowing fuses at random times.
Fast-forward to the first of the year. As of 1 January 2023, the owner came off the road and began operating as a local, home-every-night driver, and the radio came out of the truck to be used in his shack at home, except that it still had that pesky fuse-blowing problem, which is where I entered the story.
The owner explained the entire history to me, and after some judicious questions, I determined that the fuse most often blew while the truck was in motion, though it would occasionally blow when the vehicle was stationary. He wanted me to find and fix the fuse blowing issue once and for all… and oh yeah - plug in the speaker, too. He shipped the radio to me, but he did not include the power cable, so I had to use a bench cable with a fuse holder (Figure 3) to power the radio for testing, to which I added Anderson PowerPole® for my own convenience.
I put the radio on the bench and connected up the incoming power, a dummy load, and an external speaker… and the radio worked normally. I then decided to connect it to an antenna - my trusty Ed Fong J-Pole - and to use it on the Tuesday net. The radio worked flawlessly, albeit through the external speaker. I decided that I would try to emulate the rough ride of the truck where the radio used to live… I picked it up and I shook it while it was operating. I shook it, I banged on it, I bounced it on a stack of towels… and nothing. It never missed a beat. Next, I tried some “unusual attitudes” as we used to call it in flight school. I started twisting and turning the radio while bouncing it on the stack of towels. Finally, when I stood the unit up on end with the front face upwards, and bounced it hard on the towel stack, it finally blew the fuse. I replaced the fuse and tried the same thing again, and once more the fuse blew with the same maneuvers.
So, what did I prove? Well… I showed two things to be true :
The original problem was related to the occasional and unpredictable blown fuse on the incoming power line. The ID-800H was vehicle-mounted in a 2022 Peterbilt 579 (Figure 2) Class 8 truck-tractor. The secondary problem was a lack of audio from the radio unless an external speaker was installed and connected. This problem showed up when the radio came back from the second repair shop. The owner is an over-the-road long-distance trucker who has historically had his radio - CB’s and ham - all repaired at truck stop radio shops.
When the problem first appeared, the owner took the radio to a radio shop at a truck stop in Carlisle, PA. Of course, as nothing was actually repaired other than replacement of the blown fuse, the problem eventually re-occurred. At this point, the owner replaced the fuse himself, and the radio worked as it was intended to, for a while. At some point, the owner happened to have some time to kill while in Kenly, NC, so he took the radio to a radio shop at a truck stop there. This time when he reinstalled it in the truck, it worked again, except that there was no audio from the internal speaker. This was annoying, and the owner assumed that the repairman simply forgot to reconnect the speaker wire harness to the mainboard on re-assembly. However, due to the ambient noise level in the truck, he customarily used an amplified external speaker anyway, so he didn’t fret too much about it. Needless to say, the radio was still blowing fuses at random times.
Fast-forward to the first of the year. As of 1 January 2023, the owner came off the road and began operating as a local, home-every-night driver, and the radio came out of the truck to be used in his shack at home, except that it still had that pesky fuse-blowing problem, which is where I entered the story.
The owner explained the entire history to me, and after some judicious questions, I determined that the fuse most often blew while the truck was in motion, though it would occasionally blow when the vehicle was stationary. He wanted me to find and fix the fuse blowing issue once and for all… and oh yeah - plug in the speaker, too. He shipped the radio to me, but he did not include the power cable, so I had to use a bench cable with a fuse holder (Figure 3) to power the radio for testing, to which I added Anderson PowerPole® for my own convenience.
I put the radio on the bench and connected up the incoming power, a dummy load, and an external speaker… and the radio worked normally. I then decided to connect it to an antenna - my trusty Ed Fong J-Pole - and to use it on the Tuesday net. The radio worked flawlessly, albeit through the external speaker. I decided that I would try to emulate the rough ride of the truck where the radio used to live… I picked it up and I shook it while it was operating. I shook it, I banged on it, I bounced it on a stack of towels… and nothing. It never missed a beat. Next, I tried some “unusual attitudes” as we used to call it in flight school. I started twisting and turning the radio while bouncing it on the stack of towels. Finally, when I stood the unit up on end with the front face upwards, and bounced it hard on the towel stack, it finally blew the fuse. I replaced the fuse and tried the same thing again, and once more the fuse blew with the same maneuvers.
So, what did I prove? Well… I showed two things to be true :
- That the fuse did blow after some violent jarring of the radio.
- The behavior was repeatable.
Now it was time to open up the radio and the service manual, and to start investigating the internals. It just so happens that I have one of these radios myself, which may come into play for some comparisons, if necessary.
I disconnected the radio and opened it up, and the very first thing that I noted was that the speaker wire harness was indeed connected to the mainboard. This meant that I would need to dig a bit into the audio issue as well, to get to the cause of that problem. More on that later.
As usual, I began by looking for any visible indications of something burnt, arced, or otherwise indicating a short circuit, but nothing jumped out at me. I removed the RF shield from the mainboard to look underneath it as well. Finding nothing the easy way, I decided to emulate my vigorous treatment of the radio. With a new fuse in the power wire fuse holder and the unit power on, I began to gently poke and prod various points in the radio using a plastic alignment tool as the prod. Nothing happened until I prodded the wire harness for the cooling fan. As soon as I touched this wire pair, it arced against the chassis rear heat sink and the fuse blew. Success!
Closer examination revealed a chafed area (Figure 4) in the red wire to the fan, exposing the bare wire inside the red insulation. I surmise that this wire would, with enough of a jar to the radio, move just enough to short against the heat sink, causing the fuse to blow. A look at the schematic shows that the fan is fed almost full supply voltage, dropped only by a 6.8Ω resistor in series with the fan positive lead. The fan supply, on lead HVI, traces back from the 6.8Ω fuse R102 directly to the incoming 13.8VDC power inlet. Fan control is all done on the fan’s negative lead. Thus, shorting the fan’s positive lead to ground is tantamount to placing a direct short on the positive power feed to the radio, causing the fuse to open.
The repair was fairly simple. Using the tip of a hobby knife, I gently lifted the latch of the red wire terminal in the fan harness plug, and pulled the wire and terminal from the plug (Figure 5). I then slipped a short piece of narrow heat shrink tube on the wire and hit it with hot air from the heat gun. Once the HST was shrunk in place, I inserted the terminal back into the plug (Figure 6). After that, it was a simple matter to re-mount the fan and plug it in onto the mainboard.
Now it was time to look for the audio problem. As a refresher, the radio had audio only via an external speaker. No sound came from the internal speaker, which was plugged in onto the mainboard in the correct location. The owner had thought that perhaps the last repairman had forgotten to connect the speaker harness, but that was not the case, as I discovered. I had to start somewhere, so I started at the speaker connector on the mainboard. To my surprise, there was a strong audio signal there at the speaker header. Thus, the problem had to be in either the speaker or its connecting harness. I took a “AA” battery that I keep on hand with a clip lead soldered to each end, and I did a momentary “scratch” test of the speaker, which responded with a typical characteristic static scratch. The speaker coil was intact, which narrowed down the problem. It had to be a harness issue.
I took a good close look at the plug end of the harness and found that one of the wires was out of the plug body, and therefore was not able to make contact with the header pin. My guess is that when the last repairman disconnected the speaker on opening the radio, he pulled the wire from the plug (Figure 7) and did not notice it. I certainly did not notice it until I had reason to take a good look at the plug. I pushed the wire all the way into the plug body and connected the harness. Magic! The dead audio was once again alive.
I reassembled the radio and once more subjected it to a violent thrashing in an attempt to blow another fuse, but failed to do so. I took that as a sign that the repair was effective, so I boxed it up, less the power cord, and shipped it back to Tennessee, together with my invoice and two spare fuses.
What lessons can be learned from this repair? I see a couple of them. Let’s take them one at a time, and explore their validity and value.
First off, I think that the fix isn’t made until the repair person actually finds the cause of the problem. Fixing a symptom, in this case the blown fuses, does not repair the equipment, not so long as the root cause has not been located. Without correcting the root cause, the symptom is bound to re-appear at some point in time. The fact that this radio was riding around in an eighteen-wheeler, and taking an aggressive hammering as the truck traveled America’s highways and byways, meant that the unit was being put through some unusual operating conditions. It was when I emulated that pounding ride that I was able to reproduce the symptom, reliably and repeatedly. Think outside the box and consider all operating conditions when tracking down a symptom like this one.
Second, it is obvious to me that the second repair shop failed to do any kind of active post-repair testing of the radio, because if such testing had been done, it would have been obvious that a new problem had been introduced in that the speaker audio output was nil. Perhaps the repairman thought that the radio had been like that when it came to him, but the owner says otherwise. It is important that the repaired radio be put through all of its paces post-repair just to make sure that something like this has not happened. It is understandable how it happened; it is inexcusable that it left the shop like that.
I am not saying that my repairs are perfect - I am human, and so I will make mistakes and miss things, as I have in the past. However, any shop should be able to pick the low-hanging fruit and fix the easy ones. The more difficult ones just take a little bit longer, or maybe a lot longer.
See you next month!
I disconnected the radio and opened it up, and the very first thing that I noted was that the speaker wire harness was indeed connected to the mainboard. This meant that I would need to dig a bit into the audio issue as well, to get to the cause of that problem. More on that later.
As usual, I began by looking for any visible indications of something burnt, arced, or otherwise indicating a short circuit, but nothing jumped out at me. I removed the RF shield from the mainboard to look underneath it as well. Finding nothing the easy way, I decided to emulate my vigorous treatment of the radio. With a new fuse in the power wire fuse holder and the unit power on, I began to gently poke and prod various points in the radio using a plastic alignment tool as the prod. Nothing happened until I prodded the wire harness for the cooling fan. As soon as I touched this wire pair, it arced against the chassis rear heat sink and the fuse blew. Success!
Closer examination revealed a chafed area (Figure 4) in the red wire to the fan, exposing the bare wire inside the red insulation. I surmise that this wire would, with enough of a jar to the radio, move just enough to short against the heat sink, causing the fuse to blow. A look at the schematic shows that the fan is fed almost full supply voltage, dropped only by a 6.8Ω resistor in series with the fan positive lead. The fan supply, on lead HVI, traces back from the 6.8Ω fuse R102 directly to the incoming 13.8VDC power inlet. Fan control is all done on the fan’s negative lead. Thus, shorting the fan’s positive lead to ground is tantamount to placing a direct short on the positive power feed to the radio, causing the fuse to open.
The repair was fairly simple. Using the tip of a hobby knife, I gently lifted the latch of the red wire terminal in the fan harness plug, and pulled the wire and terminal from the plug (Figure 5). I then slipped a short piece of narrow heat shrink tube on the wire and hit it with hot air from the heat gun. Once the HST was shrunk in place, I inserted the terminal back into the plug (Figure 6). After that, it was a simple matter to re-mount the fan and plug it in onto the mainboard.
Now it was time to look for the audio problem. As a refresher, the radio had audio only via an external speaker. No sound came from the internal speaker, which was plugged in onto the mainboard in the correct location. The owner had thought that perhaps the last repairman had forgotten to connect the speaker harness, but that was not the case, as I discovered. I had to start somewhere, so I started at the speaker connector on the mainboard. To my surprise, there was a strong audio signal there at the speaker header. Thus, the problem had to be in either the speaker or its connecting harness. I took a “AA” battery that I keep on hand with a clip lead soldered to each end, and I did a momentary “scratch” test of the speaker, which responded with a typical characteristic static scratch. The speaker coil was intact, which narrowed down the problem. It had to be a harness issue.
I took a good close look at the plug end of the harness and found that one of the wires was out of the plug body, and therefore was not able to make contact with the header pin. My guess is that when the last repairman disconnected the speaker on opening the radio, he pulled the wire from the plug (Figure 7) and did not notice it. I certainly did not notice it until I had reason to take a good look at the plug. I pushed the wire all the way into the plug body and connected the harness. Magic! The dead audio was once again alive.
I reassembled the radio and once more subjected it to a violent thrashing in an attempt to blow another fuse, but failed to do so. I took that as a sign that the repair was effective, so I boxed it up, less the power cord, and shipped it back to Tennessee, together with my invoice and two spare fuses.
What lessons can be learned from this repair? I see a couple of them. Let’s take them one at a time, and explore their validity and value.
First off, I think that the fix isn’t made until the repair person actually finds the cause of the problem. Fixing a symptom, in this case the blown fuses, does not repair the equipment, not so long as the root cause has not been located. Without correcting the root cause, the symptom is bound to re-appear at some point in time. The fact that this radio was riding around in an eighteen-wheeler, and taking an aggressive hammering as the truck traveled America’s highways and byways, meant that the unit was being put through some unusual operating conditions. It was when I emulated that pounding ride that I was able to reproduce the symptom, reliably and repeatedly. Think outside the box and consider all operating conditions when tracking down a symptom like this one.
Second, it is obvious to me that the second repair shop failed to do any kind of active post-repair testing of the radio, because if such testing had been done, it would have been obvious that a new problem had been introduced in that the speaker audio output was nil. Perhaps the repairman thought that the radio had been like that when it came to him, but the owner says otherwise. It is important that the repaired radio be put through all of its paces post-repair just to make sure that something like this has not happened. It is understandable how it happened; it is inexcusable that it left the shop like that.
I am not saying that my repairs are perfect - I am human, and so I will make mistakes and miss things, as I have in the past. However, any shop should be able to pick the low-hanging fruit and fix the easy ones. The more difficult ones just take a little bit longer, or maybe a lot longer.
See you next month!
Icom ID-4100A – March 2023
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Sometimes, you have to repair - or at least I have to repair - my own equipment. And, sometimes the old adage about “getting what you pay for” is true. In this case, it certainly came true. I had been having occasional problems with my Icom ID-4100A (Figure 1) powering itself off, most often at the end of a transmission, but occasionally during receive operations. |
Figure 1 : Icom ID-4100A
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There was no rhyme or reason to when this would happen. It might happen twice during a net, or it might go several weeks without occurring. I was always able to restore the radio to operation by power-cycling the power supply, and I was therefore half convinced that the problem was internal to the radio, so I set about trying to locate the problem.
My first step was to take the ID-4100A out of service. I unplugged the power cord at the “T” connector (Figure 2) that is so common on mobile radios today. The radio that I was swapping in there temporarily, an Icom ID-800H, had the same type of power cord, so it was a plug-in replacement as far as the connections went - power cord and antenna cable.
I fired up the ID-800H and all was well. I set the ID-4100A aside for repairs when I could fit the job into my schedule, reasoning that there was no hurry as I had yet another 2-meter set available if the ID-800H should fail, a Yaesu FT-1900. In this way, I should not have to resort to my handheld for the nets, right?
Two weeks go by, meaning four nets in which I participated, for two of which I was the Net Control Station, and all was working well. I sat there thinking through the ID-4100A problem, and poring over the schematic and block diagram, looking for the most likely place to start in troubleshooting the shutdown issue, but had not yet reached any definite conclusions.
Another week goes by, with two more nets. During the Thursday net, the old faithful ID-800H shut down, exactly as the ID-4100A had been doing! Stop the truck and back it up. I concluded now that the problem was not in the radio after all. At this point, I began suspecting the power supply instead, as it was common to the two radios. I decided to watch carefully the next time the radio went dead to see how the power supply behaved. I got a bit of a surprise doing that.
The next time the radio fell dead was the Tuesday net two weeks later. Throughout the net, I sat there staring at the front of the power supply, studying its backlighting and the output monitor meter. What I saw there puzzled me for a few minutes… the power supply showed a momentary spike in output current just as the radio died, but then dropped to a zero-current state.
The output voltage had momentarily sagged a little bit, but then jumped right back up to the normal 13.8VDC available output. This told me that the problem was neither the radio nor the power supply, but something in between them. The only thing between the power supply and the radio was the six-port Powerpole® distribution block that I had mounted behind the desk, and of course the power cables themselves. No fuses had blown through all of this, with either radio.
I went to the Powerpole® distribution block and carefully examined both it and the power cords connected to it. Much to my surprise, I found that the port to which my 2-meter radio was connected looked melted, very slightly on the black connector shell, but quite heavily on the red shell (Figure 3). This melting had occurred on both the cable end (Figure 4) and the distribution block port. I disconnected the cable from that port and got another surprise. Inside the red shell of the cable, the contact was not all the way out to the end of the connector shell as it should have been. Instead, it was pushed back a little bit, enough to cause the connection made when the plug bodies were joined to be somewhat less than optimal. Apparently, this connection would occasionally open, usually when heavier current was drawn during transmission. The heat caused by the resistance formed there is what melted the connector bodies.
This particular cable was an ebay.com buy that I picked up before I got my Powerpole® assembly kit in house. I needed a power pigtail for the mobile-type radios, so I bought a couple of inexpensive ones on the auction site.
My guess is that the actual contact was never fully inserted into the connector body far enough to lock into place. It simply pushed away from its mating contact, maintaining a light touch with its mate, but opening up under load. This caused me to inspect the second cable that I bought at that time, but it was assembled correctly, with the contacts in place where they belonged.
The fix for the cable was simple. Cut off the melted connector and crimp on a new pair of Powerpole® connectors. I keep the Powerpole® parts on hand, so that was no problem. The repair to the distribution block was not quite as simple.
The distribution block has a metal cover secured in place by four small flat-head machine screws, so disassembly was easy. I removed the screws and lifted off the cover, exposing the inside of the unit. Inside, there was a small printed circuit board (Figure 5) having bus bars along its outer edges to help handle the rated current of the unit. Each of the Powerpole® shells was installed to a blade-type contact that is soldered into the PCB. I fooled around with trying to release the contact from the body and to slide the body off, but that was going nowhere fast. Ultimately, I decided to try a more direct approach. I took a pair of pliers and simply crushed the melted red connector body, causing it to separate from its contact a bit.
Then it was just a matter of using pliers to grip and wiggle it off the contact, sort of like pulling a tooth (Figure 6). After that, all that was left was the job of forcing a new connector body down in place of the melted one. The black connector body was intact, so I was able to leave that one alone.
After the connector shell was replaced, reassembly of the distribution block was the reverse of the disassembly procedure. The only tricky part was reinstalling the three miniature truss-head machine screws that secure the PCB to the lower enclosure half, as they are buried down between the Powerpole® shells.
With the distribution block repaired and reassembled (Figure 7), it was time to put it back into service, which I did. The new connectors on the power cable, properly assembled this time, worked as they should, and the problem of the dead radio has not occurred since the repairs.
The lesson in all of this is to inspect every piece of kit that you buy, because even “brand new” items might be defective. Had I inspected this cable before use, I may have noticed that the contact was not seated and I could have corrected it. All that would have been needed was to properly seat the contact in the connector shell by pushing in until it clicked into place. I failed to do so, and ended up with a mystery to solve as a result.
See you next month!
I went to the Powerpole® distribution block and carefully examined both it and the power cords connected to it. Much to my surprise, I found that the port to which my 2-meter radio was connected looked melted, very slightly on the black connector shell, but quite heavily on the red shell (Figure 3). This melting had occurred on both the cable end (Figure 4) and the distribution block port. I disconnected the cable from that port and got another surprise. Inside the red shell of the cable, the contact was not all the way out to the end of the connector shell as it should have been. Instead, it was pushed back a little bit, enough to cause the connection made when the plug bodies were joined to be somewhat less than optimal. Apparently, this connection would occasionally open, usually when heavier current was drawn during transmission. The heat caused by the resistance formed there is what melted the connector bodies.
This particular cable was an ebay.com buy that I picked up before I got my Powerpole® assembly kit in house. I needed a power pigtail for the mobile-type radios, so I bought a couple of inexpensive ones on the auction site.
My guess is that the actual contact was never fully inserted into the connector body far enough to lock into place. It simply pushed away from its mating contact, maintaining a light touch with its mate, but opening up under load. This caused me to inspect the second cable that I bought at that time, but it was assembled correctly, with the contacts in place where they belonged.
The fix for the cable was simple. Cut off the melted connector and crimp on a new pair of Powerpole® connectors. I keep the Powerpole® parts on hand, so that was no problem. The repair to the distribution block was not quite as simple.
The distribution block has a metal cover secured in place by four small flat-head machine screws, so disassembly was easy. I removed the screws and lifted off the cover, exposing the inside of the unit. Inside, there was a small printed circuit board (Figure 5) having bus bars along its outer edges to help handle the rated current of the unit. Each of the Powerpole® shells was installed to a blade-type contact that is soldered into the PCB. I fooled around with trying to release the contact from the body and to slide the body off, but that was going nowhere fast. Ultimately, I decided to try a more direct approach. I took a pair of pliers and simply crushed the melted red connector body, causing it to separate from its contact a bit.
Then it was just a matter of using pliers to grip and wiggle it off the contact, sort of like pulling a tooth (Figure 6). After that, all that was left was the job of forcing a new connector body down in place of the melted one. The black connector body was intact, so I was able to leave that one alone.
After the connector shell was replaced, reassembly of the distribution block was the reverse of the disassembly procedure. The only tricky part was reinstalling the three miniature truss-head machine screws that secure the PCB to the lower enclosure half, as they are buried down between the Powerpole® shells.
With the distribution block repaired and reassembled (Figure 7), it was time to put it back into service, which I did. The new connectors on the power cable, properly assembled this time, worked as they should, and the problem of the dead radio has not occurred since the repairs.
The lesson in all of this is to inspect every piece of kit that you buy, because even “brand new” items might be defective. Had I inspected this cable before use, I may have noticed that the contact was not seated and I could have corrected it. All that would have been needed was to properly seat the contact in the connector shell by pushing in until it clicked into place. I failed to do so, and ended up with a mystery to solve as a result.
See you next month!
MFJ-259 HF/VHF SWR Analyzer - February 2023
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This month’s case history is a slight departure from the norm, in that it involves the repair of a piece of test equipment. Notably, the unit under repair is one that I had already done some repair work to, prior to donating this piece to the Club for the test and repair bench. On a recent Saturday afternoon, Frank N3PUU had occasion to use the MFJ-259 SWR Analyzer while setting up the VHF station for an upcoming contest. Unfortunately, the unit did not operate as expected, and Frank left me a note to that effect. Naturally, I picked up the unit and brought it home for repair. What should have been a quite simple repair job turned into a little bit more than I had bargained for. The reported problem was that the meter was not reading, meaning that there was no indication of the tested SWR value. A quick check verified the condition, showing that the LCD panel was operational as to displaying the test frequency, but the meter movement was inoperative. However, I noticed that the meter came alive when I happened to jar the unit when I went to place it on the bench. That gave me a hint as to where to look for the problem. |
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Diving in “under the hood”, so to speak, I quickly found some cracked solder joints on the unit’s main printed circuit board. There are two meters on the front panel of this unit. One is the SWR meter, and the other is a resistance meter. These two meters are connected to the main PCB via a three-wire harness with a 90° plug at its end (Figure 1). The plug connects to a three-pin right-angle pin header on the PCB. It was this header that had the cracked solder joints (Figure 2). A simple fix - I simply reflowed the solder on those pins and the meters worked as intended. However, I did not stop there.
You see, I had been bothered by this unit ever since I put it on the test and repair bench. I felt that I did not do as thorough a refurb job on this unit as I could have, and this was borne out by the fact that Frank had trouble with the unit when he tried to use it. One of the items that I had intended to replace but did not was the SO-239 jack on the top of the unit. I decided to go ahead and give the whole unit a closer look and to replace the SO-239 jack.
Replacement of the SO-239 connector requires removal of the main PCB, which in turn requires desoldering of the two pushbutton switches and the BNC jack on the unit’s upper surface. The SO-239 itself is connected to the main PCB in an unusual fashion. The center pin of the SO-239, when the main PCB is in place, sits about an eighth of an inch above the PCB. That gap is simply filled with solder at the factory. Each of the two mounting screws used for the SO-239 has a solder lug installed under its nut. The lugs are then bent over to reach the main PCB and are soldered to pads on the PCB. These solder lugs also do not quite reach the board surface, and so their gaps are also solder-filled in production (Figure 3). Large solder bridges of this type are prone to cracking with time, a condition with which I was not happy. I therefore decided to correct this as well.
Diving in “under the hood”, so to speak, I quickly found some cracked solder joints on the unit’s main printed circuit board. There are two meters on the front panel of this unit. One is the SWR meter, and the other is a resistance meter. These two meters are connected to the main PCB via a three-wire harness with a 90° plug at its end (Figure 1). The plug connects to a three-pin right-angle pin header on the PCB. It was this header that had the cracked solder joints (Figure 2). A simple fix - I simply reflowed the solder on those pins and the meters worked as intended. However, I did not stop there.
You see, I had been bothered by this unit ever since I put it on the test and repair bench. I felt that I did not do as thorough a refurb job on this unit as I could have, and this was borne out by the fact that Frank had trouble with the unit when he tried to use it. One of the items that I had intended to replace but did not was the SO-239 jack on the top of the unit. I decided to go ahead and give the whole unit a closer look and to replace the SO-239 jack.
Replacement of the SO-239 connector requires removal of the main PCB, which in turn requires desoldering of the two pushbutton switches and the BNC jack on the unit’s upper surface. The SO-239 itself is connected to the main PCB in an unusual fashion. The center pin of the SO-239, when the main PCB is in place, sits about an eighth of an inch above the PCB. That gap is simply filled with solder at the factory. Each of the two mounting screws used for the SO-239 has a solder lug installed under its nut. The lugs are then bent over to reach the main PCB and are soldered to pads on the PCB. These solder lugs also do not quite reach the board surface, and so their gaps are also solder-filled in production (Figure 3). Large solder bridges of this type are prone to cracking with time, a condition with which I was not happy. I therefore decided to correct this as well.
Another poor manufacturing technique, in my view, was the manner in which the BNC jack and the pushbutton switches were connected. The two pushbutton switches are normally-open switches that, when pressed, connect their respective circuits to ground. The way that MFJ chose to implement this was to bend one solder lug of each switch over and solder them to the solder lug under the nut on the BNC jack (also shown in Figure 3). It was a stretch at best, and it put undue stress on the bodies of the pushbutton switches. As it turned out, when I removed these switches, I found that the bodies of both switches were cracked. Solution? Two new switches… which turned out to be an adventure in and of itself.
I installed the new SO-239 to the enclosure. Then, I went over the main and display PCB’s carefully, touching up any solder joints that looked the least bit suspicious. I then installed the main PCB to the enclosure, and I added lengths of bus wire between the mainboard solder pads and the SO-239 center pin and also at the solder lugs on its mounting screws (Figure 4). Next, I installed the BNC jack and the two pushbutton switches, wiring them up to the main PCB as they were originally. I added some bus wire to connect the grounded sides of the pushbutton switches to the BNC jack ground lug to make it a more comfortable fit. Now for the moment of truth.
I connected the battery banks (there are two of them) and powered up the unit, only to find that the LCD panel was not working. Now what? Did I damage the LCD panel in doing my solder touch-ups? I did not think so, but I went ahead and removed the main PCB again so that I could inspect the display PCB carefully. As luck would have it, I found nothing wrong there.
I sat back and thought about it a little bit, and then I decided to eliminate possibilities by testing the unit operation at each step of assembly. I installed the main PCB and checked the LCD operation, finding that it worked normally. I connected the SO-239 jack and again checked the LCD operation, and it worked just fine, which makes sense, as the jack was open.
So, next I wired up the BNC jack, and as expected (as this jack too was open), the LCD operated as it was meant to. I then connected the first of the two pushbutton switches, the one labeled “GATE”. Once again, the LCD panel worked normally. Finally, a bit confused, I connected the “INPUT” pushbutton switch. Of course, now the LCD panel did not work.
As mentioned earlier, the pushbutton switches are normally-open switches, so connecting that last switch should not have made any difference, but it did… which meant that the switch was obviously not open! I checked the switch with an ohmmeter, and sure enough, it was a normally-closed switch that had somehow gotten mixed in with my supply of normally-open switches. Swapping out that switch for another (verified NO) switch from my stock solved the problem (Figures 5 & 6).
The lesson to be learned from this repair is actually a dual lesson.
When things don’t work out the way that you expect them to, think it through and carefully go back over what you have done and especially any changes that you have made.
A thorough search will usually turn up the culprit.
See you next month!
I installed the new SO-239 to the enclosure. Then, I went over the main and display PCB’s carefully, touching up any solder joints that looked the least bit suspicious. I then installed the main PCB to the enclosure, and I added lengths of bus wire between the mainboard solder pads and the SO-239 center pin and also at the solder lugs on its mounting screws (Figure 4). Next, I installed the BNC jack and the two pushbutton switches, wiring them up to the main PCB as they were originally. I added some bus wire to connect the grounded sides of the pushbutton switches to the BNC jack ground lug to make it a more comfortable fit. Now for the moment of truth.
I connected the battery banks (there are two of them) and powered up the unit, only to find that the LCD panel was not working. Now what? Did I damage the LCD panel in doing my solder touch-ups? I did not think so, but I went ahead and removed the main PCB again so that I could inspect the display PCB carefully. As luck would have it, I found nothing wrong there.
I sat back and thought about it a little bit, and then I decided to eliminate possibilities by testing the unit operation at each step of assembly. I installed the main PCB and checked the LCD operation, finding that it worked normally. I connected the SO-239 jack and again checked the LCD operation, and it worked just fine, which makes sense, as the jack was open.
So, next I wired up the BNC jack, and as expected (as this jack too was open), the LCD operated as it was meant to. I then connected the first of the two pushbutton switches, the one labeled “GATE”. Once again, the LCD panel worked normally. Finally, a bit confused, I connected the “INPUT” pushbutton switch. Of course, now the LCD panel did not work.
As mentioned earlier, the pushbutton switches are normally-open switches, so connecting that last switch should not have made any difference, but it did… which meant that the switch was obviously not open! I checked the switch with an ohmmeter, and sure enough, it was a normally-closed switch that had somehow gotten mixed in with my supply of normally-open switches. Swapping out that switch for another (verified NO) switch from my stock solved the problem (Figures 5 & 6).
The lesson to be learned from this repair is actually a dual lesson.
- First, I should have done a more complete job on this unit the first time around, before I put it on the Club’s test and repair bench.
- Second, and more to the point, remember that each and every “repair” that is made can actually introduce a previously non-existing problem.
When things don’t work out the way that you expect them to, think it through and carefully go back over what you have done and especially any changes that you have made.
A thorough search will usually turn up the culprit.
See you next month!
Henry 1KD-5 Amplifier
Henry 1KD-5 Amplifier - January 2023
Let me start out this month’s case history with an apology. No repair should take as long as this one (and one other, to be discussed in another article) did. There is no real excuse other than that the job was a bear to do, and I kind of dragged my feet on digging into the guts of this thing. I am talking about the Henry Radio 1KD-5 HF linear amplifier. This was a circa 1977 model, heavier than you can believe, with a one-tube grounded-grid circuit. The tube is a PL3-500ZG tube of about four and a half inches diameter, nestled inside an external glass bell chimney. The tube socket is buried deep inside the unit, behind a board that carries the tuning coils for the amplifier.
I am getting ahead of myself. Let’s start at the beginning. The owner brought this unit to me, explaining that the tube would light, and then go out, then light again, and then go out, and would repeat this behavior while switched on. He also told me that he was in no hurry to get it back.
I set up my 30A 230V outlet with the correct receptacle to match the Henry’s power cord, and fired it up to confirm the reported behavior. It took just about a minute or so before the on/off action became evident, so I set out to find the cause. As it turned out, that was the easy part. Some gentle pressure on tube while it was out would cause it to light up again.
The problem was that the tube socket, a humongous ceramic thing about three inches square and about three-eighths of an inch thick, had fatigued with age and the effects of heat. The result was that the contacts that grip the tube pins had relaxed quite a bit - enough so that when they got hot, the circuit would open until they cooled down, at which time the circuit would close and the process would repeat. Solution? A new tube socket.
I tracked down a source for the socket, but I had to wait for the socket to come in from China, and I had to order two of them at an exorbitant price to get the one that I needed. I buttoned up the amp and set it aside to wait for the part to come in.
Let me start out this month’s case history with an apology. No repair should take as long as this one (and one other, to be discussed in another article) did. There is no real excuse other than that the job was a bear to do, and I kind of dragged my feet on digging into the guts of this thing. I am talking about the Henry Radio 1KD-5 HF linear amplifier. This was a circa 1977 model, heavier than you can believe, with a one-tube grounded-grid circuit. The tube is a PL3-500ZG tube of about four and a half inches diameter, nestled inside an external glass bell chimney. The tube socket is buried deep inside the unit, behind a board that carries the tuning coils for the amplifier.
I am getting ahead of myself. Let’s start at the beginning. The owner brought this unit to me, explaining that the tube would light, and then go out, then light again, and then go out, and would repeat this behavior while switched on. He also told me that he was in no hurry to get it back.
I set up my 30A 230V outlet with the correct receptacle to match the Henry’s power cord, and fired it up to confirm the reported behavior. It took just about a minute or so before the on/off action became evident, so I set out to find the cause. As it turned out, that was the easy part. Some gentle pressure on tube while it was out would cause it to light up again.
The problem was that the tube socket, a humongous ceramic thing about three inches square and about three-eighths of an inch thick, had fatigued with age and the effects of heat. The result was that the contacts that grip the tube pins had relaxed quite a bit - enough so that when they got hot, the circuit would open until they cooled down, at which time the circuit would close and the process would repeat. Solution? A new tube socket.
I tracked down a source for the socket, but I had to wait for the socket to come in from China, and I had to order two of them at an exorbitant price to get the one that I needed. I buttoned up the amp and set it aside to wait for the part to come in.
Fast-forward a few months. I have the part in hand, and I finally put the Henry back on the bench. Major disassembly of the unit was required to enable access to the tube socket. I removed the glass chimney and the tube and set them aside for safe-keeping. The chimney is probably irreplaceable at this point, and the tube runs anywhere from two to four hundred dollars, depending on availability and seller. I did not want anything to happen to them!
After removal of the sheet metal covers and shields, I had to laboriously remove the forced-air cooling system fan and motor. Next, it was necessary to dismount the tuning coil board and carefully move it out of the way. A large toroidal transformer was next to be removed for access to the tube socket, which had two of its heavy wire leads soldered to the tube socket terminals. My 240-watt soldering gun was required to desolder these connections. Now I was able to get to the tube socket and ground lug mounting hardware and remove the machine screws, lock washers, and nuts. Finally, again using my 240-watt gun, I was able to desolder the capacitors from the connecting tabs of the tube socket and lift the socket out.
At the solder station, I moved the ground lugs from the old tube socket to the new one. I also drilled the tube socket solder lugs as necessary for the heavy wire from the toroidal transformer to fit. Then it was time to reassemble the whole shooting match, which was quite a tedious task due to hardware locations and difficulty in reaching some of the screws to install lock washers and nuts on them. I finally got the tube socket mounted, and then soldered its capacitor connections in place. I reinstalled the toroidal transformer and soldered its leads to the tube socket.
Reassembly of the rest was the reverse of the disassembly procedure, with the exception that I replaced many of the sheet metal screws due to their holes having been stripped or worn oversized.
After final reassembly, it was time to test and align the amplifier, which went exactly according the manual instructions with no surprises. All in all, it was a rewarding repair, though I could never charge the owner the full amount of time spent on the unit.
Sometimes, repairs are just tedious replacement of connecting parts rather than active or even passive components. This was one of those times. None the less, it was a necessary repair in order to bring the amplifier back to operational status.
See you next month!
After removal of the sheet metal covers and shields, I had to laboriously remove the forced-air cooling system fan and motor. Next, it was necessary to dismount the tuning coil board and carefully move it out of the way. A large toroidal transformer was next to be removed for access to the tube socket, which had two of its heavy wire leads soldered to the tube socket terminals. My 240-watt soldering gun was required to desolder these connections. Now I was able to get to the tube socket and ground lug mounting hardware and remove the machine screws, lock washers, and nuts. Finally, again using my 240-watt gun, I was able to desolder the capacitors from the connecting tabs of the tube socket and lift the socket out.
At the solder station, I moved the ground lugs from the old tube socket to the new one. I also drilled the tube socket solder lugs as necessary for the heavy wire from the toroidal transformer to fit. Then it was time to reassemble the whole shooting match, which was quite a tedious task due to hardware locations and difficulty in reaching some of the screws to install lock washers and nuts on them. I finally got the tube socket mounted, and then soldered its capacitor connections in place. I reinstalled the toroidal transformer and soldered its leads to the tube socket.
Reassembly of the rest was the reverse of the disassembly procedure, with the exception that I replaced many of the sheet metal screws due to their holes having been stripped or worn oversized.
After final reassembly, it was time to test and align the amplifier, which went exactly according the manual instructions with no surprises. All in all, it was a rewarding repair, though I could never charge the owner the full amount of time spent on the unit.
Sometimes, repairs are just tedious replacement of connecting parts rather than active or even passive components. This was one of those times. None the less, it was a necessary repair in order to bring the amplifier back to operational status.
See you next month!
Kenwood TM-241A
Kenwood TM-241A 2M Transceiver - December 2022
Every now and then, a repair comes along that is both easy and difficult at the same time. This month’s repair case history is one of those occasions. This is the story of a simple - and not so simple - repair of a Kenwood TM-241A fifty-watt 2-meter mobile transceiver.
The radio came to me with the complaint of being inoperative on transmit, which was easily verified with a simple output test into my Bird 43 directional wattmeter and a dummy load. The Bird 43 showed zero output power from the radio. During this test, however, I also noted that the unit failed to maintain its last-used settings, which told me that there was a second problem with the radio, and therefore the need for some deeper troubleshooting.
Armed with a TM-241A service manual and schematic, I set out to isolate the output power problem first. It took only a few minutes with an oscilloscope to determine that the signal was present at the input of the final amplifier, but that there was no output from that amplifier stage. A quick check of the power supply voltages to the final amp IC (Kenwood calls this the power module) showed that the operating voltages were correct, meaning that the IC was most likely a failed device. A quick online search showed that the power module, a Toshiba S-AV17, was available from many sources, including East Coast Transistor, an authorized Kenwood parts distributor. In the interest of sticking with original factory replacement parts, I ordered the IC from ECT and waited for it to come in.
Before ordering the IC, I went ahead and checked out the most likely cause of the radio failing to store any settings - a failed memory “keep-alive” battery. Kenwood did not make it very easy to replace this battery, which is a CR2032 coin cell with an insulating outer ring and welded tabs for connection to the printed circuit board. When installed, this coin cell is sandwiched between two insulators, one of which is double-sided adhesive foam which is used to affix the coin cell to the PCB.
Every now and then, a repair comes along that is both easy and difficult at the same time. This month’s repair case history is one of those occasions. This is the story of a simple - and not so simple - repair of a Kenwood TM-241A fifty-watt 2-meter mobile transceiver.
The radio came to me with the complaint of being inoperative on transmit, which was easily verified with a simple output test into my Bird 43 directional wattmeter and a dummy load. The Bird 43 showed zero output power from the radio. During this test, however, I also noted that the unit failed to maintain its last-used settings, which told me that there was a second problem with the radio, and therefore the need for some deeper troubleshooting.
Armed with a TM-241A service manual and schematic, I set out to isolate the output power problem first. It took only a few minutes with an oscilloscope to determine that the signal was present at the input of the final amplifier, but that there was no output from that amplifier stage. A quick check of the power supply voltages to the final amp IC (Kenwood calls this the power module) showed that the operating voltages were correct, meaning that the IC was most likely a failed device. A quick online search showed that the power module, a Toshiba S-AV17, was available from many sources, including East Coast Transistor, an authorized Kenwood parts distributor. In the interest of sticking with original factory replacement parts, I ordered the IC from ECT and waited for it to come in.
Before ordering the IC, I went ahead and checked out the most likely cause of the radio failing to store any settings - a failed memory “keep-alive” battery. Kenwood did not make it very easy to replace this battery, which is a CR2032 coin cell with an insulating outer ring and welded tabs for connection to the printed circuit board. When installed, this coin cell is sandwiched between two insulators, one of which is double-sided adhesive foam which is used to affix the coin cell to the PCB.
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Accessing the battery is the not-so-easy part and involves removal of the front bezel of the radio, followed by the removal of a metal structural cover, and finally the front panel display unit printed circuit board. At this point, the battery voltage can be measured easily. When measured in-circuit, the coin cell showed a voltage of only 0.36 volts. With the battery basically “dead”, it was necessary to continue the disassembly. To do so, the main front panel PCB is removed from the chassis to allow access to the coin cell, which is mounted between this PCB and the main chassis. Care must be taken when de-soldering the coin cell so as not to overheat and damage the PCB.
An important point is to be certain to use JIS screwdrivers for this job, especially for the tiny screws that secure the metal front structure to the main chassis. It is extremely easy to strip the heads of these screws if the wrong screwdriver is used. Polarity alignment of the coin cell is aided by indications on the PCB referring to the + and - terminal connect points.
I ordered the coin cell from East Coast Transistor in the same order as the power module, and then I sat back and waited for the parts to come in. Delivery took eight business days. The parts arrived well-packaged and in good condition, though they had to travel via ground transportation due to the fact that the coin cell is a lithium battery and thus falls under certain transportation restrictions.
Installation of the coin cell and reassembly of the front panel was basically a reversal of the disassembly process. I noted that the control pushbutton extenders have a tendency to fall out when reassembling the unit. Apart from that hiccup, it is a straightforward process.
Installation of the power module, on the other hand, required removal of the main PCB from the radio chassis. I had elected not to remove this board until the new parts arrived, primarily so that the removal procedure would be fresh in my mind when it came to reassembly time.
I had taken several photographs prior to disassembly, which is a standard practice for me. This provides a reference for reassembly. In this case, it helped me to resolve a puzzle in that there is one plug with seven wires for which I could not seem to find the connect point. For several minutes, I struggled with trying to remember disconnecting the plug, but I simply did not remember unplugging it. Finally, by referring back to my photos, I realized that this is a plug that goes nowhere. It was simply hanging free underneath the loudspeaker behind the front panel. The other end of this harness is a seven-wire plug that connects to the front panel PCB.
Removing the PCB is not complex at all, and replacement of the power module on the PCB requires the normal care about excessive heat. Be aware that there are two mounting tabs on the S-AV17, which are secured to the rear of the chassis via machine screws, thus providing heat sinking for the IC. When reinstalling the PCB with the new power module, be sure to coat the rear surface of the IC with silicone thermal transfer grease for best heat transfer to the chassis. Again, be sure to use a JIS screwdriver for this task as well.
After reassembly was completed, it was time to test the operation of the repaired unit. The first thing that I checked was the ability of the radio to “remember” the last used settings. This was no problem; all worked as expected. Next up was the power output test. When tested with my faithful Bird 43 into a dummy load, the radio showed an output of >47 watts into a dummy load.
While the customer had made no mention of the settings memory issue, I would not have considered the radio to have been repaired completely if the battery had not been replaced. Had the customer squawked about the additional and not requested repair expense, I would probably have attempted to work out a parts/labor split with the customer for that specific part of the repair bill. As it turned out, the customer was satisfied with the overall repair and its cost as presented.
The moral of the story here is that there is often more to repair than just what the customer reports. A thorough repair tech will go the extra mile, though it is usually best to discuss any additional repairs with the radio’s owner before proceeding with those additional repair items.
See you next month…
An important point is to be certain to use JIS screwdrivers for this job, especially for the tiny screws that secure the metal front structure to the main chassis. It is extremely easy to strip the heads of these screws if the wrong screwdriver is used. Polarity alignment of the coin cell is aided by indications on the PCB referring to the + and - terminal connect points.
I ordered the coin cell from East Coast Transistor in the same order as the power module, and then I sat back and waited for the parts to come in. Delivery took eight business days. The parts arrived well-packaged and in good condition, though they had to travel via ground transportation due to the fact that the coin cell is a lithium battery and thus falls under certain transportation restrictions.
Installation of the coin cell and reassembly of the front panel was basically a reversal of the disassembly process. I noted that the control pushbutton extenders have a tendency to fall out when reassembling the unit. Apart from that hiccup, it is a straightforward process.
Installation of the power module, on the other hand, required removal of the main PCB from the radio chassis. I had elected not to remove this board until the new parts arrived, primarily so that the removal procedure would be fresh in my mind when it came to reassembly time.
I had taken several photographs prior to disassembly, which is a standard practice for me. This provides a reference for reassembly. In this case, it helped me to resolve a puzzle in that there is one plug with seven wires for which I could not seem to find the connect point. For several minutes, I struggled with trying to remember disconnecting the plug, but I simply did not remember unplugging it. Finally, by referring back to my photos, I realized that this is a plug that goes nowhere. It was simply hanging free underneath the loudspeaker behind the front panel. The other end of this harness is a seven-wire plug that connects to the front panel PCB.
Removing the PCB is not complex at all, and replacement of the power module on the PCB requires the normal care about excessive heat. Be aware that there are two mounting tabs on the S-AV17, which are secured to the rear of the chassis via machine screws, thus providing heat sinking for the IC. When reinstalling the PCB with the new power module, be sure to coat the rear surface of the IC with silicone thermal transfer grease for best heat transfer to the chassis. Again, be sure to use a JIS screwdriver for this task as well.
After reassembly was completed, it was time to test the operation of the repaired unit. The first thing that I checked was the ability of the radio to “remember” the last used settings. This was no problem; all worked as expected. Next up was the power output test. When tested with my faithful Bird 43 into a dummy load, the radio showed an output of >47 watts into a dummy load.
While the customer had made no mention of the settings memory issue, I would not have considered the radio to have been repaired completely if the battery had not been replaced. Had the customer squawked about the additional and not requested repair expense, I would probably have attempted to work out a parts/labor split with the customer for that specific part of the repair bill. As it turned out, the customer was satisfied with the overall repair and its cost as presented.
The moral of the story here is that there is often more to repair than just what the customer reports. A thorough repair tech will go the extra mile, though it is usually best to discuss any additional repairs with the radio’s owner before proceeding with those additional repair items.
See you next month…
ICOM IC-706 HF/6M/2M Transceiver - November 2022
Sometimes you wish that the customer would just be honest with you and tell you what really happened, and this month’s At the Repair Bench is an example of one of those times. It all began with a phone call from a gentleman out in western Pennsylvania. I should have realized that something was wonky when he couldn’t tell me who it was that referred him to me - or maybe he wouldn’t say. Anyway, he asked if he could ship his faithful Icom® IC-706 to me for repair, saying only that the front panel was “dead”. Naturally, I agreed to look at it, so he shipped it in.
He did an over-the-top job of packing the radio and mic, going so far as to buy some Lowe’s sheet foam and cut custom blocks to surround the radio, and then gluing the blocks together to make two half shells that fit the radio quite well, and also fit the carton perfectly. Kudos on that part! He lost some points, however, when I got into the repair… but I am getting ahead of myself.
After unpacking the radio, I put it on the bench and connected it to my power supply and dummy load, and powered it on… or at least I tried to power it on. Nothing happened. The unit was stone cold dead and unresponsive. I took the cover screws out and lifted the top cover, and I saw immediately what the problem was.
The Icom® IC-706 has a removable front panel, which connects behind the panel to a set of eight spring contacts, which in turn connect to the main PCB via a “flex circuit” or Kapton cable. Connection to the main PCB is made through the use of a top-entry edge connector that is surface-mount soldered to the main PCB. This connector was off the PCB and floating free inside the radio, tethered to the end of the Kapton cable.
Here is the part where the owner lost points… someone had been inside the radio and most likely pulled that connector off the board. How do I know this? Simple… the speaker connection (the speaker is mounted to the top cover) was unplugged.
Sometimes you wish that the customer would just be honest with you and tell you what really happened, and this month’s At the Repair Bench is an example of one of those times. It all began with a phone call from a gentleman out in western Pennsylvania. I should have realized that something was wonky when he couldn’t tell me who it was that referred him to me - or maybe he wouldn’t say. Anyway, he asked if he could ship his faithful Icom® IC-706 to me for repair, saying only that the front panel was “dead”. Naturally, I agreed to look at it, so he shipped it in.
He did an over-the-top job of packing the radio and mic, going so far as to buy some Lowe’s sheet foam and cut custom blocks to surround the radio, and then gluing the blocks together to make two half shells that fit the radio quite well, and also fit the carton perfectly. Kudos on that part! He lost some points, however, when I got into the repair… but I am getting ahead of myself.
After unpacking the radio, I put it on the bench and connected it to my power supply and dummy load, and powered it on… or at least I tried to power it on. Nothing happened. The unit was stone cold dead and unresponsive. I took the cover screws out and lifted the top cover, and I saw immediately what the problem was.
The Icom® IC-706 has a removable front panel, which connects behind the panel to a set of eight spring contacts, which in turn connect to the main PCB via a “flex circuit” or Kapton cable. Connection to the main PCB is made through the use of a top-entry edge connector that is surface-mount soldered to the main PCB. This connector was off the PCB and floating free inside the radio, tethered to the end of the Kapton cable.
Here is the part where the owner lost points… someone had been inside the radio and most likely pulled that connector off the board. How do I know this? Simple… the speaker connection (the speaker is mounted to the top cover) was unplugged.
The repair was simple enough. Fortunately, no damage was done to the PCB - all of the pads were intact and in fact had plenty of solder on them. All I had to do was to reflow the solder on the connector pins once I put the connector in position. Of course, I had to remove the FL-100 CW Narrow Filter and the FL-223 SSB Narrow Filter to allow clear work access to the connector location on the PCB. The Kapton cable itself was unhurt, so after I resoldered the connector in place, I was able to simply re-insert the Kapton cable into the connector slot.
Was it embarrassment? Was it ignorance? Who knows? All that I know is that the radio performed properly once the repair was made, and I repeated the inbound packing job for the outbound trip back to the owner. A simple repair with a nebulous cause… but one thing is certain. That connector most likely did not fall off by itself.
I would much rather have the customer tell me the truth as to what is going on when a unit comes in for repair, as it takes a lot of the guesswork out of the equation. See you next month!
Was it embarrassment? Was it ignorance? Who knows? All that I know is that the radio performed properly once the repair was made, and I repeated the inbound packing job for the outbound trip back to the owner. A simple repair with a nebulous cause… but one thing is certain. That connector most likely did not fall off by itself.
I would much rather have the customer tell me the truth as to what is going on when a unit comes in for repair, as it takes a lot of the guesswork out of the equation. See you next month!
Heathkit® HP-23B Power Supply - October 2022
Every now and then, I will come across a repair that should have been avoidable with proper equipment maintenance. Unfortunately, some maintenance is beyond the skill set of the equipment owner. This month’s repair is just such a repair.
The Heathkit® HP-23B is a multi-output power supply used in conjunction with several of that company’s ham radio equipment offerings. The PSU provides outputs of 700VDC at 250mA, 350VDC at 150mA, 250VDC at 100mA, -100VDC at 20mA, and 12.6VAC at 5.5A. The incoming power is a standard 120VAC at about 350 watts. The unit is heavy, weighing in at about sixteen pounds.
Every now and then, I will come across a repair that should have been avoidable with proper equipment maintenance. Unfortunately, some maintenance is beyond the skill set of the equipment owner. This month’s repair is just such a repair.
The Heathkit® HP-23B is a multi-output power supply used in conjunction with several of that company’s ham radio equipment offerings. The PSU provides outputs of 700VDC at 250mA, 350VDC at 150mA, 250VDC at 100mA, -100VDC at 20mA, and 12.6VAC at 5.5A. The incoming power is a standard 120VAC at about 350 watts. The unit is heavy, weighing in at about sixteen pounds.
www.radiomuseum.org
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www.radiomuseum.org
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This particular HP-23B came to me with the complaint that it would repeatedly trip the chassis-mounted 2.92-ampere circuit breaker. The owner would press the reset button, and almost immediately it would trip out again. This behavior led me to believe that there was either a dead short circuit somewhere, or a condition that would mimic a short circuit very closely. Time for some detective work.
The circuit breaker is installed in the power transformer primary winding circuit, so I started out by applying some judicious use of the ohmmeter to the primary circuit, only to find that all was as it should be. No problem there, so it was off to the secondary side.
I decided to eliminate the simplest circuit first, which is the 12.6VAC output. This circuit is simply taken from an isolated secondary winding and carried to the output plug as the two secondary leads from the winding - no additional components. There was no short circuit there, and the winding resistance was reasonable. I moved on to the DC outputs.
The three DC output circuits are easily isolated by opening a single wire lead in each circuit, which would then allow for resistance readings to ground at various points in those circuits. It did not take very long to identify an “almost” shorted 125µF filter capacitor in the medium/low voltage output circuit. This capacitor had extremely high leakage and would obviously require replacement.
I next removed and bench-tested all of the electrolytic capacitors in the unit, and I found relatively high leakage in three of the four 125µF filter capacitors and in one of the 40µF electrolytics used in the -100VDC bias circuit.
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There is a company called Hayseed Hamfest (www.hayseedhamfest.com) who provides re-cap kits for this power supply. The beauty of their kit is that the unit retains its original appearance, though it functions like brand new. The kit is offered in multiple formats - either with or without the smaller capacitors, and in standard or in increased working voltage versions. I ordered up the standard voltage kit in the complete (all capacitors) version and sat back and waited for it to come in. |
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The installation of the capacitors was a straightforward repair, as all of the parts are intended to fit exactly in place of the originals so as to preserve the factory appearance of the unit. Post-repair testing showed all to be functional and the voltages to be at the manual specified levels. I wrapped and boxed the PSU and shipped it back to the owner (after he paid my bill, of course!)
This put another one in the “WIN” column, but it did reveal an important point. When it comes to older electronic equipment, periodic maintenance should probably include at least the testing of, if not the actual replacement of, any and all capacitors that are likely to age poorly. This obviously includes filter capacitors, as they do a huge part of the job when making clean DC from the transformed AC supply.
See you next month!
Simpson 260 Series 5 Analog VOMM - September 2022
A few weeks ago, I received a carton in the mail, with a plea for help tucked into the carton alongside a Simpson 260 Series 5 analog VOMM. (Yes - VOMM is correct in this case, as the meter is a volts, ohms, and milliamperes meter.) The owner wrote that it had quit working in all modes and he had no idea why. Of course, I was up for the challenge, and it turned out to be quite interesting.
I first verified that there was no response in the meter on any function or scale. I then took off the rear cover - four screws and it was off. The first thing that I noticed was that there was no battery installed for the ohmmeter function. The 260 uses a total of five cells – four “AA” cells and one “D” cell to power the ohmmeter. Naturally, I installed a set of cells and tested the ohmmeter function again, to find that it was still inoperative.
A few weeks ago, I received a carton in the mail, with a plea for help tucked into the carton alongside a Simpson 260 Series 5 analog VOMM. (Yes - VOMM is correct in this case, as the meter is a volts, ohms, and milliamperes meter.) The owner wrote that it had quit working in all modes and he had no idea why. Of course, I was up for the challenge, and it turned out to be quite interesting.
I first verified that there was no response in the meter on any function or scale. I then took off the rear cover - four screws and it was off. The first thing that I noticed was that there was no battery installed for the ohmmeter function. The 260 uses a total of five cells – four “AA” cells and one “D” cell to power the ohmmeter. Naturally, I installed a set of cells and tested the ohmmeter function again, to find that it was still inoperative.
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I began a more thorough examination of the meter componentry, looking for burned components or broken wire solder points. What I found instead was quite surprising, and goes to show that you cannot always believe what people say. A close inspection revealed that the PCB on which most of the meter’s components are installed was cracked along its left (from the rear) side, about an inch in from the edge of the board and at an angle from the outer corner towards the center.
I removed the PCB to examine the opposite (foil) side, and found that five traces were broken along the crack. This might turn out to be a simple repair. I began by applying some cyanoacrylate glue to the crack to strengthen the board. When the glue had cured, I simply solder-bridged the cracks in the foil traces, a task made easier by the fact that the traces were solder-covered. I re-installed the “AA” and “D” cells, and tested the meter. Full operation was restored! I did some cleaning of the switches and pots inside the meter with some DeoxIT® Gold, cleaned up the exterior, and secured the back to the meter assembly.
The meter’s folding handle was quite misshapen (read : bent). I decided to remove it and repair it. The handle is secured by a shoulder bolt on either side of the case, so I removed those bolts. The handle itself is a sandwich of metal encased by a plastic covering, making it a simple task to straighten the handle completely, and then to re-bend it to its proper contour. I then re-installed the handle and the job was done.
I do not know how the PCB got broken, but it is quite obvious to me that the unit had been dropped at some point in its history, based upon the way the handle was bent. I also have a hard time believing that the owner was unaware of the broken PCB, especially as he had removed the battery for shipping the meter. He also did not take any care in packing the meter for shipment – he simply stuck it in a carton with its test leads, but with no wrapping or packing at all, leaving the meter free to bounce around in the carton. Needless to say, it did NOT go back to him the same way.
I removed the PCB to examine the opposite (foil) side, and found that five traces were broken along the crack. This might turn out to be a simple repair. I began by applying some cyanoacrylate glue to the crack to strengthen the board. When the glue had cured, I simply solder-bridged the cracks in the foil traces, a task made easier by the fact that the traces were solder-covered. I re-installed the “AA” and “D” cells, and tested the meter. Full operation was restored! I did some cleaning of the switches and pots inside the meter with some DeoxIT® Gold, cleaned up the exterior, and secured the back to the meter assembly.
The meter’s folding handle was quite misshapen (read : bent). I decided to remove it and repair it. The handle is secured by a shoulder bolt on either side of the case, so I removed those bolts. The handle itself is a sandwich of metal encased by a plastic covering, making it a simple task to straighten the handle completely, and then to re-bend it to its proper contour. I then re-installed the handle and the job was done.
I do not know how the PCB got broken, but it is quite obvious to me that the unit had been dropped at some point in its history, based upon the way the handle was bent. I also have a hard time believing that the owner was unaware of the broken PCB, especially as he had removed the battery for shipping the meter. He also did not take any care in packing the meter for shipment – he simply stuck it in a carton with its test leads, but with no wrapping or packing at all, leaving the meter free to bounce around in the carton. Needless to say, it did NOT go back to him the same way.
NanoVNA - August 2022
Fairly recently, another member – Rich Subers W2RHS – and I entered into a complex trade agreement wherein he would give me an unbuilt MFJ antenna tuner kit for me to build, and in exchange, I would replace his failed NanoVNA with a new and slightly larger one. Rich threw in the failed NanoVNA, so I figured I would give it a try to see if I could repair it.
This particular NanoVNA is encased in a multi-piece 3-D printed plastic enclosure, which does a good job of protecting the unit. It would also serve to keep things in place post-repair. Rich had told me that the unit worked, even though there was no display on the screen, as he could connect it to his phone or PC and use the functions of the NanoVNA with no trouble via the software. I suspected that the problem was in the display backlight wiring.
We were fairly sure that the problem was a bad solder joint underneath the display, which was attached to the main PCB with some strong adhesive. The first question was whether or not I could successfully separate the display and the main board. I tried using some monofilament line to cut the adhesive, but the line kept breaking, Ultimately, I tried using some AWG24 solid copper wire, which did the trick nicely.
Once I had the unit open, I powered it up and starting putting localized pressure on the end of the Kapton cable that connects the display to the main board. There are about twenty individual connections carried in that cable, so I had to determine which ones were faulty. It soon became evident that there were multiple joints open, as pressing on various connections would illuminate different LED’s in the four-LED backlight system.
These wire connections are on a pitch or spacing of about 0.050”, so I chose NOT to attack this job with a soldering iron. Instead, I fired up my hot air reflow gun and heated the area with the hot air while placing light pressure across the entire Kapton cable end. This approach was quite successful, restoring the unit backlight to full operation. The best part was that no undue damage was done to the Kapton cable, and I did not have to worry about solder bridges.
I flipped the display back in place, where the original adhesive bonded back together and held the display tightly. I then reassembled the plastic enclosure and the job was complete. Just for fun, I tried a calibration and then swept some coax, some lamp cord, and a couple of antennas. All worked as it should.
Because Rich had a new unit and did not want this one back, I casually offered it to the first taker on a Tuesday Noonday Net, and it was gone inside of five minutes. Now, another member, Anthony Cerami N2OAC, is the proud owner of a resurrected NanoVNA.
Fairly recently, another member – Rich Subers W2RHS – and I entered into a complex trade agreement wherein he would give me an unbuilt MFJ antenna tuner kit for me to build, and in exchange, I would replace his failed NanoVNA with a new and slightly larger one. Rich threw in the failed NanoVNA, so I figured I would give it a try to see if I could repair it.
This particular NanoVNA is encased in a multi-piece 3-D printed plastic enclosure, which does a good job of protecting the unit. It would also serve to keep things in place post-repair. Rich had told me that the unit worked, even though there was no display on the screen, as he could connect it to his phone or PC and use the functions of the NanoVNA with no trouble via the software. I suspected that the problem was in the display backlight wiring.
We were fairly sure that the problem was a bad solder joint underneath the display, which was attached to the main PCB with some strong adhesive. The first question was whether or not I could successfully separate the display and the main board. I tried using some monofilament line to cut the adhesive, but the line kept breaking, Ultimately, I tried using some AWG24 solid copper wire, which did the trick nicely.
Once I had the unit open, I powered it up and starting putting localized pressure on the end of the Kapton cable that connects the display to the main board. There are about twenty individual connections carried in that cable, so I had to determine which ones were faulty. It soon became evident that there were multiple joints open, as pressing on various connections would illuminate different LED’s in the four-LED backlight system.
These wire connections are on a pitch or spacing of about 0.050”, so I chose NOT to attack this job with a soldering iron. Instead, I fired up my hot air reflow gun and heated the area with the hot air while placing light pressure across the entire Kapton cable end. This approach was quite successful, restoring the unit backlight to full operation. The best part was that no undue damage was done to the Kapton cable, and I did not have to worry about solder bridges.
I flipped the display back in place, where the original adhesive bonded back together and held the display tightly. I then reassembled the plastic enclosure and the job was complete. Just for fun, I tried a calibration and then swept some coax, some lamp cord, and a couple of antennas. All worked as it should.
Because Rich had a new unit and did not want this one back, I casually offered it to the first taker on a Tuesday Noonday Net, and it was gone inside of five minutes. Now, another member, Anthony Cerami N2OAC, is the proud owner of a resurrected NanoVNA.
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Heathkit HD-1234 - July 2022
The typical ham wouldn’t usually think of an antenna coax switch as being a repairable item, but sometimes it is - especially when the name “Heathkit® ” is involved. I recently encountered a six-position (four live connections) switch, a Heathkit® HD-1234, that had two dead positions. Its owner had added another antenna, and so needed to use an additional position on the switch. Of course, I decided to give it a shot. This unit has a six-position switch mechanism which connects each of the four live connectors to a common connector in turn as the switch is rotated. The device is of a hexagonal shape, |
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with an SO-239 connector on each of five of the sides, and a ground post on the sixth side. The way the unit is designed, when a given position is selected, all of the other positions’ connectors are grounded. The connectors are labeled “1” through “4”, “C”, and “G”. The internal switching mechanism has no physical stop, which means that it can be rotated a full 360° if so desired.
The complaint was that positions “3” and “4” were defunct, with no connection to the common connector or to ground when selected. At first, it seemed like a straight-forward open circuit problem, such as a broken solder joint at each of the non-working connectors. Close examination, however, showed that all of the solder joints were intact. On the off chance that there were hidden defects there, I went ahead and reflowed the solder on all of the connectors, but to no avail. The problem still existed.
I decided that the problem had to be inside the switch itself, so I disassembled the unit, de-soldering all of the connectors from the switch. The switch is a double-sided rotary switch on a ceramic substrate, with a contact disc on either side of the ceramic base, and a fixed brush at each of the connector positions. In its assembled condition, only the ground side of the switch substrate or base is visible; the detent plate at the top conceals the upper active connection disc and brushes.
This meant that I would need to disassemble the switch to get at the upper contact disc. No problem — it is held together by a pair of machine screws with spacers, washers, and nuts. Once the switch was apart, I began to investigate just why there was no continuity at those two switch positions. What I found was a bit of a surprise. The whole problem was a heavy build-up of oxidation on the brush contacts at those two positions. The fix was fairly simple - some cotton swabs, a toothbrush, and some DeoxIT® Gold. Twenty minutes of cleaning on both sides of the ceramic disc, and the switch contacts were operational again. Another ten minutes, and the switch was reassembled and ready to go back into the unit, with a fresh application of DeoxIT® X10S on the shaft and bushing to aid in long-life operation.
I cleaned up all of the parts, including wire-brushing the threads on the SO-239 connectors. Then I re-assembled the entire unit, and soldered the connectors to the switch terminals. Testing with an ohmmeter showed good clean continuity and zero resistance through all positions of the switch. Passing 30 VDC through the switch from common to each output in turn showed zero voltage drop internally in the switch.
So what happened here? Why did only two of the switch positions have this heavy oxidation? As it turns out, the owner has had this switch in service for over thirty-five years, but he has never used anything but switch positions “1” and “2”, and never turned the switch all of the way around the dial - he simply switched it back and forth between the two positions he used. This led to a lack of “scrubbing” at the unused positions, and age and time took over from there.
Moral of the story? Sometimes, it pays to take the long way around. Exercising the switch through its entire range of travel from time to time will help to keep the contacts clean and oxidation free, allowing the switch to perform up to it design specifications. See you next month!
The complaint was that positions “3” and “4” were defunct, with no connection to the common connector or to ground when selected. At first, it seemed like a straight-forward open circuit problem, such as a broken solder joint at each of the non-working connectors. Close examination, however, showed that all of the solder joints were intact. On the off chance that there were hidden defects there, I went ahead and reflowed the solder on all of the connectors, but to no avail. The problem still existed.
I decided that the problem had to be inside the switch itself, so I disassembled the unit, de-soldering all of the connectors from the switch. The switch is a double-sided rotary switch on a ceramic substrate, with a contact disc on either side of the ceramic base, and a fixed brush at each of the connector positions. In its assembled condition, only the ground side of the switch substrate or base is visible; the detent plate at the top conceals the upper active connection disc and brushes.
This meant that I would need to disassemble the switch to get at the upper contact disc. No problem — it is held together by a pair of machine screws with spacers, washers, and nuts. Once the switch was apart, I began to investigate just why there was no continuity at those two switch positions. What I found was a bit of a surprise. The whole problem was a heavy build-up of oxidation on the brush contacts at those two positions. The fix was fairly simple - some cotton swabs, a toothbrush, and some DeoxIT® Gold. Twenty minutes of cleaning on both sides of the ceramic disc, and the switch contacts were operational again. Another ten minutes, and the switch was reassembled and ready to go back into the unit, with a fresh application of DeoxIT® X10S on the shaft and bushing to aid in long-life operation.
I cleaned up all of the parts, including wire-brushing the threads on the SO-239 connectors. Then I re-assembled the entire unit, and soldered the connectors to the switch terminals. Testing with an ohmmeter showed good clean continuity and zero resistance through all positions of the switch. Passing 30 VDC through the switch from common to each output in turn showed zero voltage drop internally in the switch.
So what happened here? Why did only two of the switch positions have this heavy oxidation? As it turns out, the owner has had this switch in service for over thirty-five years, but he has never used anything but switch positions “1” and “2”, and never turned the switch all of the way around the dial - he simply switched it back and forth between the two positions he used. This led to a lack of “scrubbing” at the unused positions, and age and time took over from there.
Moral of the story? Sometimes, it pays to take the long way around. Exercising the switch through its entire range of travel from time to time will help to keep the contacts clean and oxidation free, allowing the switch to perform up to it design specifications. See you next month!