Several years ago I replaced the “finals” in an older 2m ham transceiver. As I recall, it was fairly obvious that it was the finals that were shot, so I ordered a replacement, slipped them in, and the radio went back out the door. After it left, I noticed that the output module had a removable cover, curiosity got the best of me and I took it off. Under the cover with a circuit board of sorts with several discreet components soldered together and basically mounted to a heat sink. As I got to looking, it appeared that there was a hair-line crack in one of the traces. It made me wonder…
Skip ahead about five years and I put a surplus 2m rig in my wife’s car. I got the installation all buttoned up, keyed up the repeater but couldn’t get anyone to respond to me. A little checking and it showed the classic signs of burned up finals - barely kerchuck the repeater, but not readable on the other end. A watt meter confirmed my suspicions, but I noticed that the first time I keyed up (i.e. when it was good and cool), I got about 20 watts out for a few seconds.
I brought it back inside, and cracked the top and bottom covers. I found a familiar looking Toshiba S-AV17 power module in the back.
I’d been curious to know if that old rig just had a hairline crack or if it was more serious than that, but since it had already been repaired and returned, I’d never had the chance to find out. This time however, I popped the cover first. Initially, I didn’t see the problem, although it was fairly obvious. Since I knew I had a heat-related problem, I shot a bit of circuit cooler on the module to see if that would “fix” it. What I noticed was the frost from the cooler causing a red glow at the bottom. Sure enough, I had another crack in a trace.
The repair in the photo looks a little crude. This was my first attempt with a 15 watt iron, which I found to be pitifully inadequate since I was quite literally soldering a heat-sink. But, the fix worked.
I cleaned up the joint a little bit with a larger iron, and re-installed the rig in the car. I've only been using it sparsely for a few weeks now, but so far, so good.