Electronic – What other than capacitor rot could cause a capacitor to bulge and fail

capacitortroubleshooting

I've been teaching myself the fine art of monitor repair – replacing capacitors on a trio of lcd screens. Apparently they all had capacitors that had suffered from the plague – though a mild case of it since they bulged a tiny bit, as opposed to leaked all over the place., and replacing them has allowed two of them to be usable, least over the past week.

The third however has exhibited the same symptoms as it did before – one of the two capacitors i replaced seems to have bulged again, as did one of the ones i didn't (made by the same company that made the caps i replaced earlier). Since it was only on the board a few days, and ran for a total of maybe an hour i'm assuming its not capacitor rot.

Did i just get a bum capacitor, or could there be other issues? Is there anything i can test to try to work out the source of the problem?

Best Answer

One big issues with consumer electronics is that they use the cheapest components possible. Electrolytic capacitors in particular are notoriously failure prone.

When replacing failed capacitors it generally a good idea to replace them with ones of equal (or close) value but with a higher voltage rating. For example if the manufacturer used a 6 V capacitor on the 5 V line, you should consider using one rated for 10 or 15 V.

You probably did not get bad capacitors, assuming a reputable source, but if the replacements had the same ratings as the original, and the originals were marginal (and thus failed), the replacements were probably marginal as well.

I should probably add that heat is not your friend. How is the cooling in that part of the board? If the air vents are clogged with dust etc. that could cause them to fail as well.

If you would like another opinion see this EEV Blog forum. The conscious seems to be that you can't go wrong with Panasonic or Vishay capacitors but that many of the lesser brands will be nothing but problems. (Of course there are other good brands as well).

"That means you absolutely have to have low Rs (esr) at some high frequency. I wouldn't touch anything that didn't have a data sheet showing low esr at 100 kHz. If it isn't specified, you don't want it."