One of the questions we get a lot is how do you detect a leaky or bad capacitor. Here’s how.
Short the terminals to ensure it is not charged. If you are doing this on a motherboard with a small capacitor, just use a small screwdriver. If this is a high voltage or capacity unit UNDER NO CIRCUMSTANCES DO THIS – leave it to an expert. Large capacitors can be extremely dangerous.
Many of the digital meters today also have a capacitance check setting, simply use that setting. It not only checks for faults, but also will give you a reading of the capacitance value itself.
For most non-electrolytic capacitors a quick check (definitely bad vs. maybe good) can be done with an analog VOM. Use the highest resistance scale to measure across the terminals. When first connected there should be a short needle jump that slowly drops back to infinity. Reverse the leads and do it again, should have the same effect. Any resistance higher than infinity indicates a shorted capacitor. Lack of needle jump may indicate an open capacitor (or one of very little capacitance).
Electrolytics can also be checked with a VOM, but polarity must be observed, and the drop back to infinity may take a very long time.
Alternatively, for electrolytics and larger capacitors is to charge them with a low voltage source (e.g. 9V battery) and measure with multimeter to see if they hold the charge.
You may also notice some physical tell-tale signs before even testing. First, look for any caps that a bulding or non-uniform in shape. Second, look for any capacitor that has any kind of “goo” coming out of it. Either of those is bad news and the cap needs to be replaced.
Is the capacitor(electrolytic)bad if the needle jump over scale
then drop very slowly and get an average reading of 500 ohms or less using an analog meter?
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