HP 32SII success and woes

[jebem]

(02-20-2015 12:16 PM)Sanjeev Visvanatha Wrote:  (...) do some practice soldering before embarking on replacing the capacitor as well.

Hi, Sanjeev,

I would say the best way to check a capacitor is to replace it with a new one, assuming we do not have easy access to professional measuring equipment.
Testing DC characteristics is not enough, we would need to test AC as well.

But tantalum caps last for ages and when they fail, they usually do it in a catastrophic way by going into short circuit state.
But from your test description, that is not the case.

Your analog multimeter when set to continuity mode, will present its battery internal voltage to the probes, where the positive probe will have a negative voltage (polarity is reversed).

So to test the cap, first remove it from the circuit.
Then connect the multimeter negative probe (positive voltage) to the capacitor positive lead and the other probe to the negative lead.

If all is well, you should be able to see a fast reading towards the zero ohm in the dial (initial rush current) and then gradually the reading will increase towards infinite (it may never reach that point, depending on how large is the capacitor value and the used technology - electrolytic have leakage current all the time, for instance).

If the cap is defective by current leaking, you will get a intermediate reading. if the cap has lost the capacitance, it will not have a large initial rush current, if at all.
The best way is to shop for some new tantalum caps and compare.

One additional test, is to leave the capacitor to rest for a minute or so after doing the above test procedure.
Then use your multimeter in voltage mode to read the charged cap.
You should be able to see a fast voltage rising in the dial and then it will drop slowly (or not, it will depend on your multimeter internal impedance and cap value).

Edited to correct some language errors, as I'm not a native English.