capacitor testing

Aside from the rated capacitance value, the ESR (Equivalent Series Resistance) is probably the single most important characteristic of a capacitor used in a switch mode power supply/regulator. I heartily recommend that you invest in an ESR meter. There are a number of different models and types available. Bob Parker designed and sold a well-known and widely used kit a number of years ago, one of which I have been using for several years with great results. Here are a few links to get you started:

Different people aspire to different models, depending on personal preference, but in the end, they all do the job quite well if used properly. While there is no absolute value for the ESR of a particular type and value of capacitor, some manufacturers do publish the maximum ESR values of certain lines of their capacitors. You'll have to surf the mfr's sites to find those.

Good luck!

--
"In theory, there isn\'t any difference between theory and practice.  In 
practice, there is."  - Yogi Berra

Dave M
masondg44 at comcast dot net

And don't forget this excellent ESR meter:

Whoops hit the wrong button. Here is what I wanted to post:

Yes. The commonest failure mode of such capacitors is an increase in the equivalent series resistance (ESR). It's possible to test this in-circuit, with relatively simple equipment.

One possibility is shown at

which is something you can breadboard together pretty easily... I've built one and just have to stick it in the final case (maybe next week).

An even simpler approach is to use a function generator (you need a sine or square wave at a few tens of kHz and at somewhere around a tenth of a volt), a couple of resistors, and an oscilloscope.

See the page at

for a simple schematic, and links to a bunch of other projects.

You can buy commercial capacitor ESR testers (complete or as kits). I've heard tgood things about the AnaTek Blue meter (around $80 - see

The neat thing about all of these testers, is that you can use them in-circuit - there's no need to unsolder the capacitors prior to testing. Just make sure you've powered down the board and allowed all of the caps to self-discharge safely.

Oh... if any of the caps are bulging at the top, or have started to split at the pressure-relief seam and/or to leak fluid... you can assume that they're bad.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!

On Fri, 17 Apr 2009 09:49:58 -0500, "h.godavari" put finger to keyboard and composed:

The difficulty with testing capacitors on a motherboard is that there are several connected in parallel. This means that an ESR test may not find a bad cap because a good one may mask it. Furthermore, even if all 5 caps, say, in a parallel Vcore set are bad, you will still need to multiply the meter's ESR reading by 5 to get the individual ESR value.

- Franc Zabkar

--
Please remove one \'i\' from my address when replying by email.

It looks good Ken but a bit rich for my pocket :-(

regards hg