March 23, 2010

Caps are often the culprit...

I recently viewed an episode of the Electronics Engineering Video Blog by Dave Jones, from Australia, and was reminded that capacitors can be awful. (Go check out Dave's video blog sometime--great fun.) He did a two-part series on capacitors last fall that was entertaining and informative, and it reminded me of some of the troubleshooting and repair tasks I've faced in the past.

Seems like many of the times I've been successful in repairing broken electronic equipment it's been because I successfully identified an electrolytic capacitor that had ceased to work properly. Recently I decided to investigate the reason why one of the output channels of one of my audio mixing consoles wasn't working any more. I hooked up a signal generator to an input and began tracing the signal through to the output, and sure enough--at one point the signal looked fine going into an electrolytic cap, but it didn't show up at all on the other side. This was one channel of a stereo signal, and the signal appeared on both sides of a similar cap in the other channel, so that's what tipped me off. (It's not that I had any great understanding of the circuit function!)

Turns out that that cap was located fairly close to a voltage regulator chip that tends to run fairly warm, and I suspect that that heat contributed to the cap's failure. Electrolytics can be a weak link--they can dry out as they get old, they can be adversely affected by heat, and there are a lot of low-quality electrolytics out there.

If you're like me, you don't throw any piece of broken gear away--you salvage whatever parts you can strip from it. I would humbly suggest that you be sure to check the electrolytics you pull from old gear before you stick them in your junkbox--they could be evil!

73 de aa0ms

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