In parts. Literally. Victim of a failed attempt to perform a MARS/CAP mod. Not disassembled properly before heating up the soldering iron, but ripped apart instead.
Initial damage list:
– damaged flat cable connectors (no way to secure the cable anymore),
– various burned parts on the mainboard,
– Burned PCB traces.
Needless to say, the rig is completely dead.
Most of the burned components are here:
The charred capacitors were in stock and easy to replace. FB1001 and FB1002 (SMD-sized ferrite beads) were components I never ran into before, so I had to order these.
Progress so far:
I managed to construct my own system to secure the flatcable into the connectors. It ain’t pretty, but it will be very reliable. After replacing the capacitors I created a few (scary looking but safe) bypasses to check if the radio would wake up. It did. All I can do now is hoping that there’s no other hidden damage.
I still need to complete the reconstruction of a few burned PCB traces where the ferrite beads need to go. The main problem is that the width of these traces is a fraction of the size of the average 0603 SMD component. There is no room for errors, wish me luck. I’ll need it badly.
I never ran into a Kenwood TS-790 before, but I was surprised by its nice design and spacious PCB layout. The reported defect didn’t leave much to my imagination: the radio didn’t lock on 2 meters. All I probably had to do was to focus on the VCO.
With the service manual in one hand and a multimeter in the other I tried to set the VCO voltage at what it should be, but that didn’t work out very well. The voltage was either zero or off the scale, and changes in voltage while turning the variable capacitor inside the VCO block didn’t make any sense.
Variable capacitors (or trimmers as we call them here) are known for their reliability, even when they’re old. There’s no wear and tear either; you set them once to align something and leave them alone. I never ran into a defective one before, hence had no reason to suspect this particular component. In the end I couldn’t do much else than to reconsider TC1 being the culprit, for the simple reason that all the other components in and around the VCO block proved to be fine.
After disassembling the VCO block I removed TC1 and measured it. It was fully short circuited, with just a few gaps while turning it. After replacing the part and re-assembling the VCO block I had no trouble getting the radio back on its feet again. While I was at it anyway I did a few other checks, but apart from some minor adjustments the radio was fine. Even the backup battery (prone to leaking) was still OK.
I’m still wondering about possible causes for a trimmer to die this way. Dust maybe, moisture? I just don’t know.
I have an HP Officejet 6110 ‘all in one’ printer. It’s getting old, but as long as it works I see no reason to replace it with something else. And it kept working until a week ago. When I switched on the printer I got a lot of initialization noises, which ultimately ended in a ‘scan error’.
Hmmm. I didn’t want to scan something, I wanted to print something. Repetitive on/off switching didn’t help. It turns out that this HP will refuse to do anything when the scanner can’t initialize. Silly.
I always try to do repairs before I throw away something. In this case it proved to be an easy job: all the dust which accumulated over the years made the glass slightly opaque and impaired the effectiveness of the mirrors which reside inside the printer. Essentially the scanner system had become blind.
All it took was some disassembling, some kitchen paper and a bit of window cleaner. One reset and voilà: the thing works like new.
It’s a common problem: failing ceramic filters, thanks to a design flaw in many transceivers. The FT-857/897 are (in)famous for that, and so are a number of Kenwood models. Recently I repaired and modified four transceivers in short succession. That’s a lot, probably a matter of Murphey’s Law.
The last one on the bench was a Kenwood TS-2000, owned by my neighbor ham Jan PE1LJS. He complained about crackling noises on AM and SSB, even when no antenna was connected. I immediately recognized the problem and offered to fix his rig. In the case of the FT-857/897 only one filter has to replaced, but in case of the Kenwood I didn’t get away with that – I had to replace all three of them in order to get it fixed.
TS-2000 inside, after replacement of the three original filters (Toko).
When no DC block is located at both the input and output of these ceramic filters, a strange phenomenon occurs: electro-migration. In the end this process destroys metal, and the filter’s functionality in the process.
I’m still puzzled by the fact that this flaw is still part of many designs, and that it’s up to the ham to fix and modify the PCB’s. I took two of the original filters apart. The picture at the right shows a generous amount of copper oxide where it shouldn’t be, and other parts of the filter didn’t look much better either.
Oh well, it keeps me off the streets.
The answer is: thermal fuses / thermostats / switches. I recently had to repair (big word) my Yaesu FP-800 power supply. The fan didn’t switch on anymore, which is not a good thing when you’re busy DX’ing. I didn’t have to search long to find the defect: the thermostat (a.k.a. thermal switch), which is bolted onto the heat sink. When the temperature of the heat sink exceeds 50 degrees Celsius, the switch closes and the fan starts spinning.
At first I tried to get the original part, but I never got an answer from my Yaesu dealer. Instead I used a KSD 301, rated 50 degrees Celsius and N.O. (Normally Open), bought on eBay for less than $2. For a few bucks more I ordered one of those modern silent fans too and threw away the (very noisy) old one. Installation was a piece of cake.
Stock photo of the KSD 301 thermal switch. This one is rated 60 degrees.
When I discovered that my condenser dryer didn’t warm up, I remembered my Yaesu repair. I knew that dryers use these things too. The only difference is that a dryer uses a N.C. (Normally Closed) type and that these switches, for safety reasons, don’t return to their initial state after they cool down. You can reset them though, and that’s just what I did. It probably saved me a lot of money, as my dryer has been out of warranty for years.