Talk:Capacitance meter

Finding bad capacitors

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 61.9.55.135 (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. ;-)

Atlant 11:44, 7 July 2006 (UTC)