At The Repair Bench
Chris Prioli, AD2CS
A Monthly Column Describing A Recent Repair Bench Event
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Troubleshooting Resources
The link below is the full version of AD2CS Basic Troubleshooting of Electronic Devices and Equipment four part article starting in the September 2022 CrossTalk
W2MMD Clubhouse Test & Repair Bench
Equipment and Supplies List
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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.
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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!