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Finally got a stubborn 1980s amplifier to stop humming by swapping a single capacitor
I was ready to reflow the whole board, but on a hunch I replaced the main filter cap, a 4700uF 50V unit. The hum vanished completely, reminding me to always check the simple, high-stress parts first. Has anyone else had a 'one part fix' that saved a ton of time?
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robert_rodriguez665mo ago
Used to think chasing down every transistor was the only real way to fix old gear. Had a similar amp hum last year that drove me nuts for a weekend. Swapped the big filter cap as a last resort before giving up, and bam, silence. Thompson.tyler is totally right about starting at the power supply. It feels too easy sometimes, but those caps take the worst beating from heat and time. Changed my whole approach to save the complicated troubleshooting for when the simple stuff checks out.
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nancy8242mo ago
Right, that "it feels too easy sometimes" line really hits home. But here's what I still wonder about that approach. Once you swap the big filter cap and the hum is gone, do you ever go back and check what the old cap actually measured? I've got a bin full of those big cans where the capacitance was still fine but the ESR was shot. It's not always about it being totally dead, sometimes they're just tired. So when you say it was a last resort, did you even test it first, or did you just gamble and get lucky? Because I feel like that's the real trick, knowing when to test and when to just throw parts at it.
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