Hi all,
I recently fixed something for a friend where the problem turned out to be a faulty electrolytic cap. I got the problem narrowed down to a specific
circuit but could not determine the exact fault by in-circuit measurements. I had it narrowed down to 3 possible components. I ended up "fixing" it by just throwing new components at it and it worked when I changed the cap. I initially checked if the cap was shorted, and it wasn't, it wasn't measuring a particularly low resistance either and it had none of the typical physical signs of being worn out.
The cap is 220uF. I tested the cap out of circuit with first an LCR meter and then a DMM. Pictures are below. (Sorry for the crap quality. I smashed the lens on my phone)
LCR measurements:
Nothing about these LCR readings scream dead electrolytic capacitor to me? Capacitance on point ✔ ESR OK ✔ DCR a little low but ✔
At this point I don't see why changing this cap fixed anything, so, I decided to also check the capacitor with a DMM.
DMM shows very low resistance and a super wonky capacitance measurement, so, now the DMM has told me the cap is faulty.
LCR works by analyzing an impedance and, I think, the DMM may be analyzing a time constant or something to get the values. So then I'm wondering,
which one is lying? What is going on here? Am I missing something? Is the LCR meter faulty? Anyone?