How are Caps Checked? by ohlm meter?

[joeeye]

How are caps checked? I never ventured this far and can use a little push what to do.

I have a MSI 939 motherboard thats for a desktop computer that was intermittenly working to not working.

Everything points to the mobo, a fast look at the board seems okay, so I took readings of all the caps on the whole motherboard, all the same kind of caps read all the same olhm, except for this one particular set of matching caps, there are about 7 of these matching caps and only two of them read the same ohlm, the rest are quite a bit different, and none match.

Being new to the world of caps any advice would help, thanks, Joe

[Per Hansson]

Re: How are Caps Checked? by ohlm meter?

You need an ESR meter, this forum section has some info:

https://www.badcaps.net/forum/forumdisplay.php?f=33

[willawake]

Re: How are Caps Checked? by ohlm meter?

like per said, thats what you need. a low ohms meter. the usual multimeters are not accurate enough or go low enough for diagnosis. but tell us your readings anyway.

spec sheets specify the guaranteed esr so new caps can differ although in my experience not by much.

existing caps on the board can read different also. not only because of their specs changing during their working life but also measurements may be inaccurate because of other caps or components nearby. thereby requiring caps to be removed for testing to check.

usually i would say anything .10 ohms and over is no good to remain on the board. but usually failed low esr caps are reading more like .30, 1.0, 2.0, 5.0, 9.0 etc. whereas good low esr caps would be measuring .06, .04, .01, .00 etc.

[joeeye]

Re: How are Caps Checked? by ohlm meter?

Sorry if I'm posting twice, I thought I was to get an emails...

I have two ohm meters... one is typical simple.

The other one is an old analog needle with a lot more sensitive ohm scale settings than a typical ohm meter, it has 1, 10, 100, 1000.

It's the 1000 scale that lets me check spark plug wires because of what they are made of (carbon) any other meter didn't do the job.

I think this will work, I'll have to dig it up and make sure it still works.

And yes willawake let me get my stuff together and I will post back what I find, I appreciate this help so much, thank you my friend, Joe

[PeteS in CA]

Re: How are Caps Checked? by ohlm meter?

Fluke (and other brands too, probably) has several DMMs that will check capacitance, but these are higher end among handhelds and are typically $200-$300. In-circuit, however, ohm meters are chiefly good for detecting shorts, and if the cap is out of the circuit, it can also detect a leaky cap. To check whether a cap has degraded, you need an ESR meter or an LCR bridge (LCR bridges are really pricey).

[joeeye]

Re: How are Caps Checked? by ohlm meter?

I'm just chasing my tail here with my ohm meters, I figured since I didn't have the ESR meter yet I'd try my ohm meters to see what the readings would be.

I don't know what meter I should get, I don't want to get a cheap meter where I find myself saying I should have gotten a better meter, also no need for me to get an over kill.

thank you everyone...

[joeeye]

Re: How are Caps Checked? by ohlm meter?

like per said, thats what you need. a low ohms meter. the usual multimeters are not accurate enough or go low enough for diagnosis. but tell us your readings anyway.

spec sheets specify the guaranteed esr so new caps can differ although in my experience not by much.

existing caps on the board can read different also. not only because of their specs changing during their working life but also measurements may be inaccurate because of other caps or components nearby. thereby requiring caps to be removed for testing to check.

usually i would say anything .10 ohms and over is no good to remain on the board. but usually failed low esr caps are reading more like .30, 1.0, 2.0, 5.0, 9.0 etc. whereas good low esr caps would be measuring .06, .04, .01, .00 etc.

Let me ask this, the computer I'm working on was intermittently working, then it got to the point where it just wouldn't boot up any more. everything checked out to the mobo being no good.

Figuring there are bad caps, and with not being able to see any that went bad, my question is can you make an assumption what reading will the bad cap(s) will read?

I know you mentioned the numbers above, but when you say anything on the board that measures .10 ohm is that with an intermitten problem?

[willawake]

Re: How are Caps Checked? by ohlm meter?

like i said on the other thread more info please. pics if possible.

[PeteS in CA]

Re: How are Caps Checked? by ohlm meter?

Well, I was not up to date on the capabilities of Fluke's DMMs. The model 110, $130 at Newark, can measure C; the mdel 87-V OTOH costs $350. There are a lot of models in between that can measure C. Other brands cost somewhat less. Pay attention to basic VDC accuracy (lower % is better), display counts of resolution (higher is better) and the maximum measureable capacitance (if that is a feature you want). I've used Fluke's products for 25 or more years and like their products, but it's your $$ and you know your intended use.

In circuit, other circuit elements (and faults) may interfere with C measurements and ohm meter checks for shorts and excessive leakage. A DMM will probably be more useful for checking voltages.

[willawake]

Re: How are Caps Checked? by ohlm meter?

i dont own anything from fluke except for a volt alert. they have nice stuff but pricey.

the esr meter comes in handy for understanding failures but really if the board is making suspected cap probs and the caps are of bad brand then total replacement of anything 1000uf and higher and also the 330uf 25v and the 470uf 16v has been proven to be a best way to proceed if not the final solution.

Still in repairs it is necessary to check other factors like software/hardware issues/psu/ram/hdd etc before coming to the conclusion that the caps are bad. Process of elimination is the best way to proceed for any computer repair. difficult to find immediately what it is but after we have eliminated what it is not then it is much easier to proceed to a final solution.

[joeeye]

Re: How are Caps Checked? by ohlm meter?

I hope I know how to send these pictures, if they come thru here are a few pictures of the caps I suspect might be going bad, I say this because there are 8 of this one type of cap, and 6 out of 8 caps I get all different ohm meter reading variations, there are only the two that give the same ohm number.

But of course nothing is true until I get my ESR meter. Its actually pretty stupid for me to figure it this way being I'm unconscious to all of this.

I did go thru a lot of diagnosing as far as the desk top failing, I built the unit and have all ways worked on it, so I feel I'm very much in tuned with it, the unit has been acting up for a little while now, and its gotten worse fairly quick, so of course I did the PSU swapping, memory, etc.. now its to the point where its acting like its not plugged in. I'm usually pretty good at diagnosing whats wrongs, so being I couldn't nail anything wrong with it I'm really focused on the mobo.

So if the caps check out okay I figure I can all ways use an ESR meter anyway...

[shadow]

Re: How are Caps Checked? by ohlm meter?

Hmm...looks like you did not post the image correctly. Willawake made a nice tutorial on how to do this in the FAQ section on this forum. The link to the thread is:

https://www.badcaps.net/forum/showthread.php?t=1868

[starfury1]

Re: How are Caps Checked? by ohlm meter?

If you are measuring in circuit your readings would have no real meaning with an analog ohm meter (multimeter).

Generally speaking
ESR is measured with AC @ a specific frequency (or frequencies)....Not DC which is what an analogue meter would be using for ohms range measurements

An analog meter will turn on semiconductors making any reading useless
(ditto what Pete S has said above)

An anologue can only really show you if its charging up, short circuit or possible leakage.
(and that depending on how you do it )

If you really want to measure ESR than a good ESR meter is really the way to go.


Caps are a fair chance but as willawake said...not the only cause