BAD caps and Oscilloscope?

[dds]

How can I identify bad cap with a help of oscilloscope?

[davmax]

Re: BAD caps and Oscilloscope?

Do you want to measure in circuit or out? It is difficult with a scope to get a good measure. If in circuit and operating you will see an increased ripple current if bad, but this needs to be compared with the normally expected ripple value.

Externally would require a powerful signal source that would depend on the type of cap and frequency of ripple in circuit.

Best method is ESR meter.

[dds]

Re: BAD caps and Oscilloscope?

Best method is ESR meter.

Sure, I have one ATLAS ESR meter - i'm still playing with it and learning. Maybe I'm confused...but how do you isolate faulty smt ceramic capacitor in circuit? It's not practical to desolder it...I was thinking maybe I could measure ripple
on the scope, and decide if the particular smt ceramic capacitor is bad/ok.


Thanks.

[starfury1]

Re: BAD caps and Oscilloscope?

smt ceramic capacitor in circuit

I think you will find an ESR meter somewhat useless for them.
an in circuit capacitance type meter may be of more use.
(these usually work by using a low Level AC frequency to calculate the capacitance, this enable them to not switch on semiconductor junctions...there are possibly with
in-circuit "let the buyer beware" situations thought)
(the above function outline is if memory serves me)


If you really in doubt best idea is replacement

I suppose it depends on what its designed to do in the circuit and the circuit and signals
if you trying to sus it out with a scope.

As davmax has said it usually a matter of knowing what should be there and comparing it with what "is there"

there is I believe, a fault that tends to happen with them (depending)
and thats physical, as in the ends break due to stress but mostly they should survive well.
(unless abused it some way)

Davmax would probably be one of the better people around here to advise on possible issues. (there are others of course)

Hope this helps anyway

Cheers

[davmax]

Re: BAD caps and Oscilloscope?

Sure, I have one ATLAS ESR meter - i'm still playing with it and learning. Maybe I'm confused...but how do you isolate faulty smt ceramic capacitor in circuit? It's not practical to desolder it...I was thinking maybe I could measure ripple
on the scope, and decide if the particular smt ceramic capacitor is bad/ok.


Thanks.

That is a very difficult situation. Ceramics are usually OK. You cannot test with ESR meter or scope. Usually if suspect replace it (low cost item). However it may not be too easy to source a replacement.