Tiny capacitors causing problem?

[Solder Boy]

Hi all, just tested 3 motherboards that either don't POST or if they do they shut off within a couple of minutes. Brought out the ESR meter and tested all the caps in the PS section of the MOBOS, they all test good.

I decided to check out the rest of the caps on the boards, some of the really puny caps have a reading of 2-4 on the ESR meter, which makes me suspect they are the culprit since all the other ones read 0.

When I say puny, I mean they are really small to the point where you need nimble fingers to take em out of the board.

[Logistics]

Re: Tiny capacitors causing problem?

On what sort of motherboards? The only time I have seen tiny capacitors in any place where it would matter is on older Pentium III boards, where you would sometimes find tiny caps around the RAM slots. I have had boards that acted finicky about their RAM, but improved after I recapped these portions with nice caps. But to have a board shut down after a few minutes means it's either over-heating or the caps are just junk. (meaning they are actually bad or they are simply the wrong type of cap for that stage, causing the board to be unstable)

[kc8adu]

Re: Tiny capacitors causing problem?

small sm caps often go bad esp msi mobo's and samsung lcd's.
they dry out and go high esr.

[gdement]

Re: Tiny capacitors causing problem?

ESR is higher on small caps. And they usually just use general purpose types for those, so those readings might be normal.

[Huckfinn]

Re: Tiny capacitors causing problem?

On a good 2.2 uf cap, esr should be about 3.5 ohms, about 1.2 for a 10 uf, and about .5 for a 47 or a 100 uf cap in any voltage range used on a motherboard.
Ultra low esr cap values will be significantly less.

Huck

[Solder Boy]

Re: Tiny capacitors causing problem?

Thanks for the info everyone, I marked the "bad" caps with magic marker so I will grab a board or two and see if I can get some info before I start getting carried away.

[PCBONEZ]

Re: Tiny capacitors causing problem?

Hi all, just tested 3 motherboards that either don't POST or if they do they shut off within a couple of minutes. Brought out the ESR meter and tested all the caps in the PS section of the MOBOS, they all test good.

Did you remove the caps to test them?
These caps are in parallel and checking 'in circuit' doesn't work.

.

[PCBONEZ]

Re: Tiny capacitors causing problem?

I have seen two (different) boards with small 4-6mm Nichicon VR caps bad/bloated.
VR is an 85c rated cap and shouldn't have been used in the first place.

Second board only had a few bad. [Don't remember which board it was.]

First was an Intel [for Gateway] socket 370 board. [Kittyhawk v1.5]
That one had 13 bloated 100uF/25v VR 6mm and 5 bloated 22uF/25v VR 5mm.

.

[linuxguru]

Re: Tiny capacitors causing problem?

Intel used Nichicon VR extensively for non-critical general-purpose bypass (other than Vcore, Vdimm, etc.) on a lot of P4-era boards. They don't usually go bad unless subjected to excessive heat, which usually only happens in SFF or similar cases.

[kc8adu]

Re: Tiny capacitors causing problem?

Intel used Nichicon VR extensively for non-critical general-purpose bypass (other than Vcore, Vdimm, etc.) on a lot of P4-era boards. They don't usually go bad unless subjected to excessive heat, which usually only happens in SFF or similar cases.

or near the vagp linear regulators.
those run hot and the caps are always shot.
good job intel!