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how can you find a bad capacitor that is mounted in a circuit board? how can you isolate a bad capacitor in a circuit board? —The preceding unsigned comment was added by 18.104.22.168 (talk • contribs) .
Measuring bad capacitors "in situ" (while still in the circuit) is notoriously difficult. Depending on what other components are in parallel with the cap, it may be impossible. If a capacitance meter gives you a reading that seems crazy, here are some of the approaches you can take are:
Consider that the cap may be shorted. Usually, an ohmmeter will detect shorts.
Observe the operation of the circuit with an oscilloscope. Coupling capacitors should couple. Filter capacitors should filter. Etc.
Bridge a second capacitor across the suspect capacitor and see if the operation changes. This is especially useful with aluminum electrolytic capacitors that dry out and lose capacitance as they age.
Remove the capacitor and test it out-of-circuit.
Replace the capacitor, at least temporarily.
Sometimes, of course, it's obvious when a capacitor has failed. Flaming tantalum and exploded aluminum electrolytics fall into this category. ;-)