Had a vintage radio blow a capacitor and take out a trace last weekend

I was working on a 1960s tube radio for a client, a Zenith model. I had just replaced the filter caps and was doing a slow power up with my variac. At about 70 volts, I heard a pop and saw a little puff of smoke. Turns out, a paper capacitor I missed had shorted, and the surge actually vaporized a section of the thin foil trace on the old phenolic board. It was a main B+ line, about an inch long. I had to stop, carefully scrape back the laminate, and solder in a jumper wire to bridge the gap. It got me thinking, do you guys always do a full recap on old gear before even testing, or do you prefer a slow power-up first to see what else might be wrong? I'm torn between saving time and risking more damage.

2 comments

2 Comments

xena6425d ago

I used to test first but @oscarwright is right, a full recap saves bigger headaches later.

oscarwright6d ago

You mentioned doing a slow power up with your variac. That's good, but you gotta check all the paper caps first, not just the filters. Those old caps are basically short circuits waiting to happen. I always do a full recap on anything with paper or wax caps before I even plug it in. The slow power up is for checking my work, not the old parts. Saves you from exactly this kind of trace repair.