Bad capacitors

[soylent]

I thought I'd try to fix a friends motherboard which appears to have a row of 4 bad capacitors(bulge at the top, some white salt like crud there as well).

The symptoms: The computer is fine once it starts, though you have to try to start it several times before it will fire up properly. And once you start it it will restart fine, it just doesn't manage 'cold starts'. It is an epox 8rda which is known to have had batches of bad caps.

Sending it in to have it fixed is not an option because: no receipt; it's been a little over 2 years(I think) so warranty might have expired; it's painful waiting weeks to have it arrive back.

Allright here's what I want to know: Those big electrolytic capacitors are for power regulation, reducing ripple and so on, so if I get a slighty larger capacitance on the replacement caps(assuming I can't exactly match the rated capacitance on the existing ones) that won't be harmful?

Are they standard electrolytic caps rated for high temps(e.g. 105C)?

There are quite a lot of caps which seem unaffected, is it a good idea to not replace them?(I allways feel like I need more arms than vishnu when I solder something )

 

[Frank]

Allright here's what I want to know: Those big electrolytic capacitors are for power regulation, reducing ripple and so on, so if I get a slighty larger capacitance on the replacement caps(assuming I can't exactly match the rated capacitance on the existing ones) that won't be harmful?

No, probably not. But the quality might be important (ie. how fast they charge / discharge), so it's best not to use cheapos, and you might want to make sure they're not tantalum caps (small chance, but if they are and you replace them with normal ones, your replacement caps will blow).

Are they standard electrolytic caps rated for high temps(e.g. 105C)?

That should be printed on them. Take them a bit higher when in doubt.

There are quite a lot of caps which seem unaffected, is it a good idea to not replace them?(I allways feel like I need more arms than vishnu when I solder something )

Yes, when the're still intact, they will probably be fine. But you might want to check the small ones right next to the electrolytic ones, to see if they didn't burst.

 

[soylent]

No, probably not. But the quality might be important (ie. how fast they charge / discharge), so it's best not to use cheapos, and you might want to make sure they're not tantalum caps (small chance, but if they are and you replace them with normal ones, your replacement caps will blow).

They're in the big 'tin can' package electrolytic caps usually come in and they have polarity printed on them. They're rated for 1200 micro farads, 105 C.

Yes, when the're still intact, they will probably be fine. But you might want to check the small ones right next to the electrolytic ones, to see if they didn't burst.

I'll check. Hopefully none of those tiny surface mounted capacitors are broken.

Thanks.

 

[Frank]

They're in the big 'tin can' package electrolytic caps usually come in and they have polarity printed on them. They're rated for 1200 micro farads, 105 C.

If they look just like regular ones and don't have strange red or yellow spots printed on them, they're normal. And such large ones are not very critical about the actual value, so it should be no problem to replace them with regular new ones that are about the same capacity.

Good luck!

 

[digitalwanderer]

Not to be a downer, but couldn't the blown caps be indicative of a different problem? Or have damaged the mobo in blowing?

I've always just pitched mobos with bad caps and I'm kind of curious now.

 

[Simon F]

Allright here's what I want to know: Those big electrolytic capacitors are for power regulation, reducing ripple and so on, so if I get a slighty larger capacitance on the replacement caps(assuming I can't exactly match the rated capacitance on the existing ones) that won't be harmful?

I'm not exactly sure what these particular ones are doing, but for power supply capacitors slightly larger would be fine.

However, much larger power filter capacitor can mean much higher peak currents through rectifier circuits so i wouldn't go overboard.

 

[Bouncing Zabaglione Bros.]

If it's one of the massive batch of faulty electolyte capacitors from a couple of years back, it might be worth considering cutting your losses and replacing the motherboard, as other capacitors will probably develop the same problem in the future.

 

[soylent]

Not to be a downer, but couldn't the blown caps be indicative of a different problem? Or have damaged the mobo in blowing?

I've always just pitched mobos with bad caps and I'm kind of curious now.

I don't think so, they aren't 'blown' per say. They look allmost exactly like these http://www.badcaps.net/images/caps/kt7/image004.png(except without the ton of dust). The motherboard works fine when it actually manages to get going so it's not likely that it is damaged.

 

[Althornin]

The symptoms: The computer is fine once it starts, though you have to try to start it several times before it will fire up properly. And once you start it it will restart fine, it just doesn't manage 'cold starts'. It is an epox 8rda which is known to have had batches of bad caps.

make sure it is the caps first.
I have had this problem before, multiple times, and it has always been a failing power supply.
However, the caps are closely related to that, all part of the power delivery system.

 

[soylent]

The symptoms: The computer is fine once it starts, though you have to try to start it several times before it will fire up properly. And once you start it it will restart fine, it just doesn't manage 'cold starts'. It is an epox 8rda which is known to have had batches of bad caps.

make sure it is the caps first.
I have had this problem before, multiple times, and it has always been a failing power supply.
However, the caps are closely related to that, all part of the power delivery system.

Yes, a poor power supply may have a lot of ripple, and that's not good for the motherboard capacitors either. But in either case, these capacitors need replacing regardless of wheter the PSU also needs replacing.