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Hey everyone... i'm back!... and with a general motherboard problem

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First post, by 386_junkie

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Hey all,

I've been away from the community for a while... and its good to be back. In the time away I've navigated various life/personal things and I'm about ready to progress some long standing projects that are still there waiting to be finished... it will happen... honest!

Anyhoo... this brings me to my questions, and please excuse, I'm a little rusty and may have to refresh my memory (no pun intended!) on some things.

1st question is on motherboard caps... and this more of just a sanity check as I know old caps can fail in numerous ways and don't even need to look bad externally to be internally dead, though has anyone found that with older 486 boards (not so much experience here... I was 386 usually) that electrolytic have prevented their motherboard from posting... especially if they haven't powered it up in a while?

2nd question... If there are no motherboard beeps... this generally suggests a CPU issue yes? I generally remember getting beeps in the past when there was RAM or graphic card issues... but found CPU issues just gave a blank screen.

3rd question... ISA / PCI POST error cards with segment displays... has anyone used them, are they helpful or limited in their diagnostic capabilities?

I suspect my issue is with a cap near the CPU, and I'm wondering if it is worthwhile to use a POST card to pinpoint the issue (if they're good and since they're cheap) before going ahead and replacing the cap... will likely replace them all anyway as part of the board refurb.

Any help or comments would be great!

Thanks

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Compaq Systempro; EISA Dual 386 ¦ Compaq Junkiepro; EISA Dual 386 ¦ ALR Powerpro; EISA Dual 386

EISA Graphic Cards ¦ EISA Graphic Card Benchmarks

Reply 1 of 2, by kixs

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Hey... good to see you back 😀

I'm not much of a hardware/electronics specialist but from experiences:

1. motherboard should POST even if caps are bad - maybe not every time - but most of the times. Unless it's shorted tantalum.
2. it's either bad CPU or motherboard.
3. diagnostics card are useful but are very limited. I like to see what is going on while booting. But if something is bad with CPU/board they are pretty much useless - only shows dashes.

Also check if your PSU is good. Sometimes they can be tricky on some boards - had a few "incompatibilities" over the years.

Requests are also possible... /msg kixs

Reply 2 of 2, by 386_junkie

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Hi Kixs,

Good to see you and thanks for the post.

When you say tantalums... could it also be the really small SMD Capacitors? or the yellow domes?

Initially I couldn't get the board to boot with a whole bunch of 72-pin simm RAM until I managed to find one single stick that worked... only one stick! The board managed to boot just the one time before I tried a different stick which didn't work. When I went back to the stick that did work it did not boot at all... no beeps, nothing. I'm wondering if because the RAM was mixed between FPM and EDO this maybe was a cause / issue? Its a UMC8881 chipset and I read that this may support EDO?

I've tried different and known to be working PSU's, VGA cards, CPU, and RAM... all to no avail... so I think all I am left with is the test card when it arrives and the prospect of changing out capacitors, both electrolytic and possibly tantalums!

Having probed some of the small SMD tantalums... some show resistance... though others seem to have really high infinite resistance... but to do continuity testing on caps properly they must first be removed from their circuit.

Edit: -
Also, the RTC Dallas MVRAM battery didn't have power while booting... though I now have a new coin cell in the Dallas RTC but it makes no difference... Would that have any effect on the bios if the Dallas RTC looses power? But then has battery attached?

Compaq Systempro; EISA Dual 386 ¦ Compaq Junkiepro; EISA Dual 386 ¦ ALR Powerpro; EISA Dual 386

EISA Graphic Cards ¦ EISA Graphic Card Benchmarks

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