testing capacitor with multimeter

[chicagodiyer]

Hi, I read that you can test whether or not a capacitor is working by using an ohm-meter. if its working the resistance will slowly increase if you connect the probe in the correct polarity and decreases if you connect it in reverse. Is this true?

I tried doing this on a power supply board, almost all of the capacitor behaved as described above, except two capacitor, does this mean these two capacitor are not working anymore?( I did not desolder the capacitors and just test them on the unplugged board)

I also did this test on a good capacitor and a slightly bulging capacitor (both were desoldered) and gave the same reading of slightly increasing resistance, does this mean the slightly bulging capacitor is still working?

is this a reliable test to figure out which capacitor to replace? (i dont have an esr meter or capacitance meter.)
thanks

[Rulycat]

Re: testing capacitor with multimeter

I made sometihng to check the capacitance a while back:
https://www.badcaps.net/forum/showthread.php?t=19156

See if this helps you in determining the status of these capacitors.

By the way, if it bulges, it's bad!

[Dgtech]

Re: testing capacitor with multimeter

Depending on your multimeter, you might have a capacitance checker on it. A lot of fluke models have one. Whenever I remove a bulged capacitor, i check it just to see how it failed. Most of them fail lower in uF value than what it's rated for. For example, a good 1000uF measures 1033uF. I would change a 1000uF if it measures less than about 980.

If you try your method with testing the lower cap, you wouldnt know it was bad. It would still charge up and discharge.

[redwire]

Re: testing capacitor with multimeter

I find the multimeter test kinda useless for capacitors nowadays. You can check for shorts or high leakage, when an ohm reading levels and stays low.
You don't know your meter's test current on ohms, so should it take 5 seconds or 15 or 30 seconds? Proof is your bulging caps look okay - at this point they should at least be low in capacitance due to electrolyte loss.
I find it best to just "shotgun" whatever you are repairing - that is, change all the electrolytics. It's quicker than troubleshooting down to the exact part and there's no risk of leaving a weak part in.

[Tube_Dude]

Re: testing capacitor with multimeter

. For example, a good 1000uF measures 1033uF. I would change a 1000uF if it measures less than about 980.

980uF in a 1000 uF capacitor is 2% of tolerance!

Usually electrolytic capacitors manufactures gave 10% or even more rated tolerance...

[Bills86e]

Re: testing capacitor with multimeter

Are there other parts on a cb that has electrolytics? It intrigues me that capacitors are
a type of rechargable battery
I'm a newby