Something different to repair this time. My neighbor’s solar inverter suddenly stopped working. He already replaced it with a newer model, but would like to keep this one as a spare. So, he asked if I could take a look.

The first thing that came to mind is: how do I power this inverter. I need to test the DC side of this – and it needs quite a high DC voltage. I solved this by wiring two transformers back-to-back with a simple bridge rectifier and a smoothing cap. So it basically serves as an isolation transformer. But with high DC voltage, you need to be really careful.

So, testing with the DC voltage – dead. Absolutely nothing. Checking the filtering caps – everything looks fine, but nothing powers on the logic board. I get power until the transformer. And yes – visual inspection reveals there’s an issue with it:

Recently, Wim, ON4CGB, went to Friedrichshafen and picked up a nice-looking Kenwood TS-950SDX.

The seller assured him the transceiver was in perfect working order and contained all filters.

As it soon turned out, it wasn’t OK; and there were filters missing. Upon receiving signals on the main VFO, the audio sounded like the transceiver was placed under water. Apparently, a known issue with these transceivers. Normally you re-solder 4 resistor networks near the CPU and you’re done.

Alas, in this case, upon opening the unit, it was immediately clear that someone had tried to patch this up; and a trace was missing to the CPU! I removed the resistor network first, so I could clean up the area. It’s quite noticeable were the trace is missing. It’s the second trace; top right; of CP1.

One of our club members recently requested me to take a look at a Kenwood TM-241 he bought a couple of years ago, but never used it. He plans to use it just for some monitoring of a couple of frequencies for local traffic.

In any case, RX is just fine, however, when clicking the PTT-button, nothing happens. No TX.

These transceivers are known to be – let’s say – “difficult” when it comes to the PA stage. They use a monolithic module which houses the complete PA. They tend to fail.

Upon inspection, someone had already been in there, and there was cooling paste between the heatsink and the module. The PA wasn’t dead either. It just wasn’t TX’ing. I remembered that the OM said that he tested the mic on another Kenwood transceiver, and it was working fine.

Could there be an issue in the front panel? I disassembled it a bit more, and yep, there’s the issue.

Kenwood used some kind of glue to tack down SMD components before soldering (I suppose they used wave soldering, hence tacking components down). Nothing wrong with that actually, however, the glue they used, absorbs moisture with time. This in turn, turns it acidic.

The trace damage can be seen in the middle – follow the trace of the center pin of the connector down, and you’ll see it. The part of the trace that goes up was also starting to go bad.