If a capacitor fails there are two cases: 1. The capacitor is part of a chip. There is no practical way for you to figure out that the capacitor has failed. Yo

If a capacitor fails there are two cases: 1. The capacitor is part of a chip. There is no practical way for you to figure out that the capacitor has failed. You will just know at best that the chip is not working right. And even if you could somehow find out that a capacitor on the chip failed there is no practical way you could replace it. In short, if a capacitor on a chip fails you will need a new chip. 2. It is a discrete capacitor. Probably surface mount soldered onto a PCB, possibly thru-hole soldered onto a PCB, or maybe some other kind of package with leads soldered across something else like the terminals of a switch or something like that. In this case it is a commodity part. You go to DigiKey or similar, find a capacitor that with the same capacitance, voltage rating, ESR, temperature range, etc,, which will be available from many manufacturers, and DigiKey will be happy to sell it to you for a few cents (plus $7 shipping). It would be nice if the device maker had to tell you the electrical parameters you need to match when buying a replacements capacitor, but it would be overkill to make all the device makers actually sell such readily available commodity parts.