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Quick Capacitance Testing Help

Discussion in 'Electronic Basics' started by [email protected], Aug 7, 2006.

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  1. Guest

    Greetings. I need some quick help on this easy question. I am testing
    capacitors in the power supply and other sections of an LCD monitor
    using a RadioShack 42-Range DMM with capacitance testing functionality.
    When I connect the leads to the electrolytic capacitors (polarity is
    accounted for), all I get is a 0.F reading (in the µF range),
    indicating overflow. This is the case when I test on other devices
    too. Is my DMM damaged or what? Could it be the range of the DMM is
    simply unable to accomidate for the capacitance? I don't personally
    believe the latter is the case at all since no type of capacitor
    registers anything with this test. If it is a problem with the
    multimeter, what other tests can I do to see if the capacitor is good
    or bad, or leaky, or whatever else it may be? Thanks a lot, I sure
    appreciate it.

    A learning, amateur electrician,
    Brad G.
     
  2. Ralph Mowery

    Ralph Mowery Guest

    Greetings. I need some quick help on this easy question. I am testing
    capacitors in the power supply and other sections of an LCD monitor
    using a RadioShack 42-Range DMM with capacitance testing functionality.
    When I connect the leads to the electrolytic capacitors (polarity is
    accounted for), all I get is a 0.F reading (in the µF range),
    indicating overflow. This is the case when I test on other devices
    too. Is my DMM damaged or what? Could it be the range of the DMM is
    simply unable to accomidate for the capacitance? I don't personally
    believe the latter is the case at all since no type of capacitor
    registers anything with this test. If it is a problem with the
    multimeter, what other tests can I do to see if the capacitor is good
    or bad, or leaky, or whatever else it may be? Thanks a lot, I sure
    appreciate it.

    A learning, amateur electrician,
    Brad G.

    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

    Are you trying to test them in the circuit ? If so the meter usually will
    not work. You will have to remove atleast one lead of the capacitor from
    the circuit to test it. This is often the case of many components. If it
    is a digital meter you may be able to test some components in the circuit,
    but not usually the capacitors.
     
  3. Guest

    Yeah, it's a digital meter. According to the manual, it's supposed to
    be able to do in-circuit testing for capacitance. It grants that
    you'll get a more accurate result if the capacitor is out of the
    circuit, but right now I'm just aiming for getting a result at all.
    Thanks once again
     
  4. If you're checking electrolytics, they may still hold a charge, which
    may affect readings.

    Keep in mind that the meter (unless it is out of the ordinary) is only
    going to let you measure capacitance. And that will be affected by
    the parallel components in the circuit. Maybe more important, many
    capacitors will fail in other ways before their capacitance changes.
    Especially electrolytics, where the failure often comes from rising
    internal resistance, so they just can't do their job right. They
    may show the proper value on the capacitance meter, but just can't
    do the work. A different kind of meter, an esr meter, is used for
    that sort of thing (and I gather is often the first thing used when
    troubleshooting where time is money); it tests to make sure the
    internal resistance of the capacitor has not gone up greatly.

    Michael
     

  5. is a better place to ask for help
    repairing something. Electrolytics need to be tested for ESR, which
    takes different equipment..


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
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