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Geeked! Fixed my first tube amp!
Well, I fixed my first tube amp today! It was a Fender Blues Deville Reissue. It was blowing fuses whenever the standby switch was turned on. After eliminating the tubes, I found an apparent short across C33. It looked like it was across both filter caps, but pulling the coil connections revealed it was on the C33 side. I cut a lead of the cap (certain that it was shorted) and found it was not! What in the world was going on?
So then I measured from the negative lead, which was still in the circuit to the clipped lead that was still in the board but seperated from the cap. Ah, there was the short, somewhere on the board. Either we were missing some of the schematic needed, or I just couldn't find the section I needed, so the circuit had to be manually traced on the board. That didn't take long, and led to the board where the tubes plug in, except all the tubes were out of the sockets.
Hmm... must be a short on a socket or something, I was thinking. But as soon as I followed the 2 wire ribbbon connector to the board, I found a tiny arc mark. One of the leads was kind of pointing down on the trace for the other lead, and apparently found a weak spot in the insulation. It was shorting to the trace. Lifting that lead up cured the problem. There was 430 volts on that line. I had bled the capacitors before checking them, but after verifying the problem was found and the unit was no longer blowing fuses, I was so excited I forgot what I was dealing with, and put my finger on a hot spot (same spot, I think) while putting it back together. So I have a little souveigner to commemorate my victory, a tiny burn hole in my fingertip.
Well, worth it, but I hope I'll remember to be more careful next time.
The customer's other complaint was that his foot switch did the opposite of what it was supposed to do. Tested it with a bench cable & found no problem. Then I found his cable & decided I'd better check it. Really odd. This cable had continuity from the sleeve on one end, to the tip on the other end & vice versa. That would definitely invert the functions. So I told my boss to just sell him another cable.
Hope this was interesting to somebody. I sure had fun.
So then I measured from the negative lead, which was still in the circuit to the clipped lead that was still in the board but seperated from the cap. Ah, there was the short, somewhere on the board. Either we were missing some of the schematic needed, or I just couldn't find the section I needed, so the circuit had to be manually traced on the board. That didn't take long, and led to the board where the tubes plug in, except all the tubes were out of the sockets.
Hmm... must be a short on a socket or something, I was thinking. But as soon as I followed the 2 wire ribbbon connector to the board, I found a tiny arc mark. One of the leads was kind of pointing down on the trace for the other lead, and apparently found a weak spot in the insulation. It was shorting to the trace. Lifting that lead up cured the problem. There was 430 volts on that line. I had bled the capacitors before checking them, but after verifying the problem was found and the unit was no longer blowing fuses, I was so excited I forgot what I was dealing with, and put my finger on a hot spot (same spot, I think) while putting it back together. So I have a little souveigner to commemorate my victory, a tiny burn hole in my fingertip.
Well, worth it, but I hope I'll remember to be more careful next time.
The customer's other complaint was that his foot switch did the opposite of what it was supposed to do. Tested it with a bench cable & found no problem. Then I found his cable & decided I'd better check it. Really odd. This cable had continuity from the sleeve on one end, to the tip on the other end & vice versa. That would definitely invert the functions. So I told my boss to just sell him another cable.
Hope this was interesting to somebody. I sure had fun.
It's a mistake you only make once, one way or another. I'm probably lucky to be alive. I never skip a single safety step anymore. One thing you don't want on your headstone is "The stupid f%#ker never learned that lesson."
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