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Thread: Can you diagnose damaged electrolytic power supply caps with dc and ac voltage meas?

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    Can you diagnose damaged electrolytic power supply caps with dc and ac voltage meas?

    Completely boneheaded move, in November 2018. I don't know the count.


    Was preparing to do some modifications on the tone stack in my amp, Fender Deluxe thing, unplugged, and hooked up one side of the bleeder wire to ground. I had the clips pushed open on the other side of the wire, to clip it to the + side of the 2 big electrolytics in the PS. One side of the open clip hit the cap wire, and the other side just touched the long bolt on the power transformer. Got a nice arc snap.

    Read all around, and some folks said that this could burn a hole inside the cap someplace due to high instantaneous current flow. <frown>

    I seem to remember some threads about diagnosing bad PS caps by measuring AC voltage at the + side, which means its measuring the ripple voltage, is that correct? If its above a certain point then replace the caps.

    I don't have a capacitance meter, but I do have an ancient scope with 10x probes. This is the HV right off the rectifier tube so its pretty HV, not sure if the scope could take it.

    Thanks

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    Supporting Member eschertron's Avatar
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    Are you saying you instantaneously discharged the caps to ground via the 'alligator' part of the jumper wire? How much metal did you vaporize?

    I don't think you want to do that over and over, but once in the life of a cap... well, I'd just soldier on after that. If the cap is damaged, then you'll hear the difference in the amp's behavior. Or you won't.

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    Lifetime Member Enzo's Avatar
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    Don't over think it. Yes, if we charge a cap and then short across it, it is POSSIBLE that the internal wire can burn open like a fuse. If teh cap still works, then that didn't happen, right?

    You wanna test a cap? Take it out, connect a 9v battery or some other source to charge it, now remove those connections and measure the stored voltage with your meter. if it has any, it ain't open.

    Or really, just measure the resistance across the cap. Does it slowly "charge up" on your meter? Then it is a cap.

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    Thanks, yeah, bonehead move, thught I was being careful but .. not.
    Thanks for the tips on checking out the cap, will do before I try to power the thing up again.

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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