Could be blown caps. You should be able to visibly tell by looking at them, if any have bulging or rounded tops then they are bad. It is possible to repair, but not easy, requires desoldering the bad ones and replacing them.

laxdragon wrote:

Could be blown caps. You should be able to visibly tell by looking at them, if any have bulging or rounded tops then they are bad. It is possible to repair, but not easy, requires desoldering the bad ones and replacing them.

I did check them and they were fine (I think, I really don't know much about electronics). Something I noticed is that the metal thingy inside the CMOS battery slot (see picture) is broken, but I don't think this is the issue because it doesn't boot at all (if it was I would expect an error at least ).

Here's a picture of it:

Oh, it can happen that a board doesn't boot without CMOS battery - I even have one here where the chip heats up rapidly when the battery voltage is missing...

AT or ATX psu are you using? Also sometimes it helps just to turn the power and allow for the board to warm up for a while then break it down again with the cmos battery removed. Also try different ram and reseat the cpu as sometimes boards can get picky.

Thanks guys, it's connected to an AT power supply. The CPU fan and the case lights turn on but that's it. I tried with different RAM and different processors, I'm beginning to think that the problem might be the battery after all.

Is it very complicated to replace the slot with another? I have a second dead motherboard that could be a donor, but my soldering skills are quite poor.

The battery holder is easy. There's probably just 2 solder points to deal with, so you can heat them alternately with your iron and gradually walk it out of the board with the other hand.
Just be careful not to heat anything for more than 2-3 seconds at a time (depending on your iron). If you have trouble getting the solder to melt, try adding more solder to the joint. That makes it easier to get heat conducted to the joint so it will all melt. Be patient and let the joints cool if you think the board might be getting too hot. You don't want to burn the via on the board, or it won't stick to solder any more.

You'll need to find a replacement that has the legs in the same places as the original. There aren't very many varieties though so chances are good your donor will match.

If you're worried about your soldering, practice on a junk board first until you feel comfortable. You really just have to get a feel for it, including developing a sense of when things are getting too hot.

If you put your finger on the top of the caps, they shouldn't feel like they have any sort of bump to them at all. If they do, they're very bad. They don't start to bulge until after they're long gone. Sometimes they never bulge but there's no easy way to detect that situation.

I highly doubt the broken battery holder is the source of the problem... my M571 will boot just fine without a battery.

The caps look OK too... that doesn't necessarily mean they aren't bad, since they can sometimes fail without bulging, but generally these boards didn't have much of a problem with capacitors despite the use of cheap crappy ones.

I'd take a very close look over the board for any nicked traces or broken components/leads. It also wouldn't hurt to pull and re-seat the BIOS chip.

Also, perhaps a dumb question, but I didn't see it mentioned... have you tried a different power supply?

shamino:

I touched them and they didn't feel bulgy at all, I don't think it's the caps. But then again, I might be wrong, as I said I'm not very good at electronics. I have not ventured in the desoldering/soldering yet, last time I did it to a keyboard connector I made a mess (melted the edge of a disk connector - I can't believe I didn't ruin the board). Thanks for the advice though!

Old Thrashbarg:

It had not ocurred to me to try a different power supply since the lights and cpu fan do turn on, but I gave it a shot and tried with another one that belongs to a working machine (a 400Mhz Celeron); it still didn't work. I looked into the BIOS chip but it seemed to be held to the board really tight - I left it like that for fear of breaking it.

Anyway, I think I'm giving it a rest for now, I don't know what else to try within my limitations. I was hoping to build a pure DOS machine with it, what's nice about it is that it has space for long ISA cards. Maybe I'll get a similar one, they are cheap here. Still, thanks for your help people!