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  • #16
    Electrolytic caps can have a number of different things wrong with them. DC leakage at working voltage is only one of them.

    It's possible for a capacitor to have high ESR or even to look like an open circuit with no DC leakage. Years ago, I had distortion in a HiFi preamp that would only go away when I removed one cap completely from the circuit. It tested OK with the equipment I had back then, but something was wrong with it.

    It's not common, but people do occasionally get a bad brand-new capacitor. I have both an ESR meter and and old impedance bridge, plus an old Heathkit Condenser Checker that will check for leakage at full voltage. If you don't have this kind of gear, checking a cap for problems is going to be very difficult. I've gotten into the habit of running some quick checks when I install new caps just to save myself headaches down the road.

    And it's going to be pretty much impossible to prove to a vendor that a cap is bad by running crude resistance tests at low voltage.

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    • #17
      If you don't have this kind of gear, checking a cap for problems is going to be very difficult.
      The simple setup described in posts #12/13 is all you need to measure leakage.
      - Own Opinions Only -

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      • #18
        Dyslexia gets me again. You are quite correct, that's what I meant; 1v = 1uA because of 1M
        Doh!
        Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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        • #19
          I'm with Rhodesplyr on this one. A cap with a bad terminal rivet will show up as having low leakage, but be useless in service. A cap tested with 9v may show low leakage but that could be a different picture at 450v.

          9v may tell you a cap is bad, but it won't tell you it's good.

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          • #20
            Originally posted by Helmholtz View Post
            The simple setup described in posts #12/13 is all you need to measure leakage.
            True, but as you said in your post, leakage is less likely to be the culprit here.

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            • #21
              Originally posted by Rhodesplyr View Post
              True, but as you said in your post, leakage is less likely to be the culprit here.
              Yes, but the OP's question was about leakage. And only the leakage test requires high voltage (could be taken from the amp).
              The importance of real cap value (as opposed to DMM cap measurement) and ESR was already mentioned in his other thread.

              And I agree that it will be impossible to prove that the caps are bad without a decent C-meter and an ESR measurement.
              - Own Opinions Only -

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