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In many cases of checking for bad electrolytic capacitors on a non-working electronic device, the number of capacitors makes it infeasible (for me anyway) to simply change out all of them one by one to find the damaged one(s) by process of elimination.

Barring obvious visual signs like bulging or leaking, are there general strategies or rules of thumb for distinguishing between those more likely and those less likely to be bad?

(For example, the one such rule I've found is that capacitors with the most current going through them are most likely to become damaged. Whether or not that is a good rule is beyond my knowledge and besides the point, but in any case, I'm imagining there are other similar rules that can be used in troubleshooting.)

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  • \$\begingroup\$ Don't change them all out one by one, change them all out at the same time. Your time is worth more than the cost of new electrolytics. If you want to select subsets, go first for the big value ones at input and output of switch mode power supplies. \$\endgroup\$
    – Neil_UK
    Aug 26, 2021 at 8:58
  • \$\begingroup\$ I've heard that viewpoint before, though for me as a novice it's going to be a major undertaking changing 20 to 50 or however many there are on the device at hand. So if there were a way to narrow it down, that would be preferable to me personally. \$\endgroup\$
    – cheaterpushups
    Aug 26, 2021 at 9:38
  • \$\begingroup\$ As for your suggestion of starting at input and outputs of power supplies, maybe make that into an answer itself, that's the kind of hint the question is asking for. \$\endgroup\$
    – cheaterpushups
    Aug 26, 2021 at 9:39

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Electronics repair guy here. First of all, if one capacitor is dead (short circuit), it will get hot if there is power applied to the shorted line.

Also, sometimes these capacitors, believe it or not, do smell. The strongest smell is from tantalum caps (pretty distinct), I don't meet many electrolytic caps (I mainly fix laptops and phones), but I can imagine it could have a smell too (not sure).

If you know which line has a short - that is you found any spot where you have a short (multimeter beeps when tested continuity to ground), it's best to apply small voltage to that line (+ on that line, - on GND) and touch the pcb around looking for a hot cap. Start with 1V/2A limit, if you don't feel anything, slowly increase voltage (or current limit if you already hit it). Some cap will have to heat up. Don't go immediately high voltage and high current, unnecessary stress for pcb that may not be designed to carry as much current as you inject into it. No need to fear that, never burned a single pcb due to overcurrent (years of experience), still, better increase injected voltage/current step by step. (maybe I burned nothing BECAUSE I was careful?)

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  • \$\begingroup\$ Thanks for the answer. Just to confirm (I'm a novice, apologies), a capacitor going bad means there is a short in the circuit board? And so the OP could have simply asked if there are strategies for locating shorts? \$\endgroup\$
    – cheaterpushups
    Aug 27, 2021 at 11:07
  • \$\begingroup\$ Yes, dead capacitor means that it starts conducting through (while it's not supposed to). And the other side of the capacitor is almost always ground. So the blown capacitor basically connects whatever line it's on straight to ground, which is the definition of a short \$\endgroup\$
    – Ilya
    Aug 27, 2021 at 11:18
  • \$\begingroup\$ If you don't find a better reply, don't forget to select an answer (well, there are no other answer to select from now, but I doubt there is much to add to this topic either) \$\endgroup\$
    – Ilya
    Aug 27, 2021 at 12:20
  • \$\begingroup\$ Thanks for your reply. I'd like to try your answer to see if helps before selecting it, and if it does help then I surely will, but with the level of knowledge I have it's going to take some effort and time to properly understand what you've explained and then to understand specifically how to go about doing it. I apologize for your effort to help not immediately resulting in any points. \$\endgroup\$
    – cheaterpushups
    Aug 29, 2021 at 7:03

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