# Capacitor specification for computer logic board replacement

I'm planning on replacing some of the electrolytic capacitors on a non-working computer logic board. I know the µf value, voltage and optimum operating temperature of the replacements, but I'm not sure what the other specifications for these should be. Specifically -

• Equivalent series resistance • Leakage current • Ripple current

Or are those values not important in this application?

• I believe manufacturer is important for electrolytic capacitors, but I don't know the exact makes to avoid. Maybe someone will reply on that. – jippie Apr 21 '12 at 22:03
• Well the problem here is that we don't actually know what the capacitors are doing. The computer logic board doesn't really describe the use of the capacitors. If I had to guess, I'd say that they're most likely related to some sort of switch-mode regulator, which can be commonly found lowering +12 V to whatever is needed, and in that case all 3 of the extra characteristics would be important. The best bet is to, if possible, hunt down the datasheet of original capacitors and see their specifications. – AndrejaKo Apr 21 '12 at 22:24

Without a schematic or service manual you don't know what other specs are important. Probably leakage current isn't a issue, but ESR and ripple current could be depending on how the caps are used. A cap in a switching power supply, particularly on the output, can quite likely require a certain ripple current rating. ESR may also matter, but if you meet the ripple current rating the ESR most likely will be good enough.

The best thing to do is to replace the caps with the same model, or look up the specs for the model and get something equivalent. However, some far east caps may be hard to trace and hard to find a datasheet for even if you could figure out who made them.

To some extent the size will tell you if ripple current is a issue. Caps that can handle more ripple current are physically larger.

If in doubt, replace with Panasonic FC series if they fit. These have low ESR and high ripple current tolerance. If the Panasonic FC are too big, then they are probably not high ripple current caps and you can replace with something like the HA series.

digi-key is your friend. Also if tight space write down case dia. [mm].

YOu can always make it fit or use larger value or voltage. Low ESR is best in every case. My link is pre-set to low ESR.

Then sort by cheapest cost and 10 pcs stock min. and select values with Ctrl key or alt or option key for multiple select filter for values and voltage

• In some applications - and especially when used as output filters for some voltage regulators, too low an ESR can (or will) lead to instability. – Russell McMahon Apr 22 '12 at 0:42
• Yes it's possible then have small ferrite beads on hand to put in series. I changed all the electrolytics on my 30 yr old Technics Receiver for \$15 or so and fixed my faults. – Tony Stewart Sunnyskyguy EE75 Apr 24 '12 at 0:31