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Testing bad capacitor in live circuit with oscilloscope?

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How can I do that? I have analogue PM3082 Fluke oscilloscope. :)

it will depend on the capacitor function, which only you know and can interpret the information to make a decision on. remove the capacitor and test it on it's own to make sure

I agree with Simon.  In many old schematics, a test point will indicate what the waveforms and voltages should be, using either a scope or DMM as recommended.

If you are winging it without such a schematic, its not easy since the test points include what should be seen give the impedance you put across the test point and ground, using the test device.

Its not safe live testing capacitors in power supplies or high voltage areas, i.e., near 50Vdc and up.  In amplifier designs of different types, the schematic usually has test points.

Is it possible to cest caps with help of function generator too? If yes, how?


well if your looking to evaluate their capacitance you can make a filter with the capacitor and from the filters response determine the value and compare it to the value marked on it. an easier way of measuring the capacitance without a capacitance meter might be to make a timing circuit with it, if a large capacitor you could time how long it takes to reach 2/3 the supply voltage (perhaps with the help of a comparator to signal the event), if small make it part of a 555 astable timer circuit and check the frequency


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