Bad caps with in-circuit ESR meter... but not high ESR?

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  • Dangermouse1
    New Member
    • Nov 2016
    • 3
    • USA

    #1

    Bad caps with in-circuit ESR meter... but not high ESR?

    Hi. I have some electronics experience and bought a MESR100 ESR meter from Ebay a few years ago to help diagnose a faulty Bose wave radio. Replaced a half dozen caps and it was back to working, yea!

    Since then I've used it on a half dozen different items for my family, often with good results. Still, there are certain things I don't understand, like why the meter works with electrolytic caps but doesn't register anything with others, like ceramic caps. And then there's this next problem...

    So, I was trying to find what's wrong with a mostly working Polk PSW111 subwoofer (click/buzzing in standby, light static when playing). When trying to test the caps I was surprised to find my meter did not respond at ALL. In the past I've seen plenty of caps with high ESR, even when leaking, they still had some response. This was the first time I've seen any that don't register at all.

    According to some other posts about fixing the PSW111 that matched my issues, I went ahead and removed two of the "Junzl" 47uF 63V caps and ordered replacement. In the mean time, I tried testing the caps again, now out of circuit, and still no response on ESR meter! Double checked ESR meter on some spare caps laying around and see it's still working fine. Checked the capacitance of the Junzl caps using another meter, and surprisingly, they still read 47uF as they should!!!

    So what's going on... are these Junzl caps just completely dried out? I ripped one open and find thin foil between layers of waxy, paper-like material. Isn't there supposed to be some electrolytic fluid of some sort in there? I would be hard pressed to find any fluid in there at all.

    For reference, the Polk speaker was made in 2009, so only 7 years old, and 10 of the 12 caps (all Junzl), from 4.7uf up to 100uf, all had no response at all from the ESR meter (the other two, still Junzl, 120uF and HV 250uF, both read fine.)
    Last edited by Dangermouse1; 12-02-2016, 03:19 PM.
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 31003
    • Albion

    #2
    Re: Bad caps with in-circuit ESR meter... but not high ESR?

    you cant reliably test caps in-circuit.
    and a lot of testers have limited range - hence not reading ceramic caps.
    the latest AVR based $10 kits can read much lower esr than older stuff and also give leakage(self discharge) values that older meters never even tried to calculate.

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