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When our motherboards or LCD's go out it is possible that the capacitors are at fault and can be easily replaced by removing and replacing the bad caps rather than buying new screens or computers. After all, replacing a cap is much faster than building a new PC.

Along those lines some of the capacitors I see on my boards are over 900µF. What is the bare minimum you need in a multimeter to test for bad capacitors (or good capacitance?)

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I'll just mention that removing the old caps can be a hugely painful process on newer boards. It appears that the ground planes on the new boards are much more efficient heat sinks than the older ones. What used to be a quick/simple cap swap with even a cheap soldering iron in the old days is now slow, difficult, and risky even with better equipment. –  Brian Knoblauch May 14 '10 at 17:18
    
@Brian, motherboards are multilayered, the last time I saw a number, suggested that most were 6 layers (of copper, sandwiched by thin layers of fiberglass board which are insulators), so it may be 8 or more layers now a days. –  mctylr May 14 '10 at 20:01
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2 Answers 2

up vote 2 down vote accepted

You need a digital multimeter (DMM) with a capacitance test mode, of adequate range. Many DMM only test a limited capacitance range. Common hobbyist DMMs may be limited to 10uF or less. So unless the capacitor is heavily damaged, it is not easy to directly measure the capacitance using a common DMM.

Preferably you want a ESR (equivalent series resistance) meter, such as this hobbyist-oriented Blue ESR meter from Anatek, if you don't have signs of physical damaged capacitors.

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+1, Good, sounds like you can probably write a short article for recent technology :-) –  nik May 15 '10 at 3:22
    
I borrowed a Fluke from a friend but it only tested to 5uF which doesn't do much for a 1000uF cap. ;) –  Xeoncross Jul 23 '10 at 0:45
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A quick reference (but a badly written one, unfortunately):

The meter that I used, to check the filter cap were an analog meter, a digital capacitance meter and an ESR meter.

I believe most of you know how to check capacitors and also generally using these type of meters. When measured with analog it showed capacitor charging and discharging, with digital capacitor tester it showed around 220 microfarad and with ESR meter it showed low ESR reading!

This proved that the bad capacitor broke-down when under full operating voltage.
Then, how do I confirm that this filter capacitor is faulty? By using an analog insulation tester.
When I connect the faulty cap to the meter and press the go button it showed a very low resistance and this is the proof of short circuit between the plate when voltage applied!
There is nothing to do with bad electrolyte. A good capacitor will just show a charge and discharge in the insulation meter just like you are checking a capacitor using analog multimeter.
In the market there are quite a number of ranges that you can buy. You get ranges of 50v, 100v, 250v,500v, 1000v and even 5000v!
If you want to test a capacitor of 100 microfarad 160v then you have to select 100v. If you select 250v, it will blow the capacitor under test.


To actually work on the bad capacitors, you may also want to look at this Recapping article.
Its well written in comparison to the other reference

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The description sounds like it assumes the capacitor under (DUT) is not in-circuit, which is not the case here. Plus an analog insulation tester is pretty old school, if not too high voltage for computer capacitors. –  mctylr May 14 '10 at 20:07
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