Basics to keep you occupied 😀 :

1. bit rot, I'd try to reflash the BIOS.
2. check if all legs of big ICs make contact
3. do the keboard LEDs light up when powered on? they should all light up briefly

Which tools do you have to troubleshoot? Oscilloscope, soldering station, eeprom programmer...?

Yes I would suspect bios chip gone bad as these micro 386 boards are near bullet proof otherwise (unless person does something dumb 😉)

The other photos have socket near the main chip populated with 74F373 while your MB doesn't have it. Is it important?

rkurbatov wrote on 2025-01-11, 22:49:

The other photos have socket near the main chip populated with 74F373 while your MB doesn't have it. Is it important?

I thought that as well when I first looked at the photo but I'm pretty sure that chip is there, you can see the legs. It appears that chip has a different top coat that makes it appear super black on camera. Looks similar to the chips in the top right corner of the photo.

Nexxen wrote on 2025-01-11, 18:26:

Basics to keep you occupied :) : […]
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Basics to keep you occupied 😀 :

1. bit rot, I'd try to reflash the BIOS.
2. check if all legs of big ICs make contact
3. do the keboard LEDs light up when powered on? they should all light up briefly

Which tools do you have to troubleshoot? Oscilloscope, soldering station, eeprom programmer...?

So....the board has been sitting a few days and I hooked it back up to see if the keyboard lights come on....which they do.
But now the board is also trying to POST and I see things on the diagnostic card. It was beeping (which it should have been since I don't have a video card in it).
I didn't have time to check anything beyond just trying to turn it on, but I'll do that as soon as I can and see where it's at now. Strange though, it's been sitting for days and days since I cleaned it...no idea why the sudden change.

Will check IC legs when I get time to inspect again, been meaning to do that.

If I had to reflash the BIOS, what chip would I select for my programmer? If it turns out to be an issue, should I reflash the same IC, or flash a new chip? Depending on what chip it is, I have some spares, just not savy in which type they used for most BIOS chips.

Oh, and tools wise. I have a 4 channel digital oscilloscope that I am fairly amateurish with, but happy to learn. I have a desoldering gun that works quite nicely. I'm comfortable soldering through hole and surface mount (to a degree), afraid of desoldering surface mount chips with many pins still 😀. But not worried about removing through hole parts (LOVE my desoldering gun). I have access to a hot air gun, but no experience using it. Other than that, multimeter and other basics.

Horun wrote on 2025-01-11, 22:42:

Yes I would suspect bios chip gone bad as these micro 386 boards are near bullet proof otherwise (unless person does something dumb 😉)

Never underestimate my abilities to do dumb things! 😁

pan069 wrote on 2025-01-11, 23:21:

rkurbatov wrote on 2025-01-11, 22:49:

The other photos have socket near the main chip populated with 74F373 while your MB doesn't have it. Is it important?

I thought that as well when I first looked at the photo but I'm pretty sure that chip is there, you can see the legs. It appears that chip has a different top coat that makes it appear super black on camera. Looks similar to the chips in the top right corner of the photo.

Yeah, sorry, it's a little bit shiny, but it's there. It's not socketed either so it looks a little weird next to the DIP 8 next to it.
The smaller chip there is a 74F08PC, and the 74F373PC is the other one as noted by rkurbatov.

Guld wrote on 2025-01-12, 01:24:

Never underestimate my abilities to do dumb things! 😁

It could've been the previous owner. I assume the PSU is known good one? Check for any signs of battery corrosion - it looks clean on the photo but depending on how the mobo was oriented most of the damage can be in one of the corners.
Other than the pins on the big chips also check the entire bottom side of the mobo. If it was dragged against another PCB there might be deep scratches, damaged or even fully cut traces. Any such damage must be repaired - tinned (and then coated, even clear nail polish will do fine) and/or a piece of wire added to bridge the gap.

If you find nothing but the mobo still randomly fails to work see if it changes with slight flexing. If so you probably have a broken via(s) somewhere and those are difficult to find.

Wash it.
Soap, water, toothbrush.
You'll be amazed how many things this fixes.

Pull battery first.

Guld wrote on 2025-01-12, 01:23:

So....the board has been sitting a few days and I hooked it back up to see if the keyboard lights come on....which they do. But […]
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Nexxen wrote on 2025-01-11, 18:26:

Basics to keep you occupied :) : […]
Show full quote

Basics to keep you occupied 😀 :

1. bit rot, I'd try to reflash the BIOS.
2. check if all legs of big ICs make contact
3. do the keboard LEDs light up when powered on? they should all light up briefly

Which tools do you have to troubleshoot? Oscilloscope, soldering station, eeprom programmer...?

So....the board has been sitting a few days and I hooked it back up to see if the keyboard lights come on....which they do.
But now the board is also trying to POST and I see things on the diagnostic card. It was beeping (which it should have been since I don't have a video card in it).
I didn't have time to check anything beyond just trying to turn it on, but I'll do that as soon as I can and see where it's at now. Strange though, it's been sitting for days and days since I cleaned it...no idea why the sudden change.

Will check IC legs when I get time to inspect again, been meaning to do that.

If I had to reflash the BIOS, what chip would I select for my programmer? If it turns out to be an issue, should I reflash the same IC, or flash a new chip? Depending on what chip it is, I have some spares, just not savy in which type they used for most BIOS chips.

Oh, and tools wise. I have a 4 channel digital oscilloscope that I am fairly amateurish with, but happy to learn. I have a desoldering gun that works quite nicely. I'm comfortable soldering through hole and surface mount (to a degree), afraid of desoldering surface mount chips with many pins still 😀. But not worried about removing through hole parts (LOVE my desoldering gun). I have access to a hot air gun, but no experience using it. Other than that, multimeter and other basics.

At this point I'd wash the board, as suggested. Just make sure it is 24 hrs dry before powering it up.
No rush.
If it issues codes it isn't dead, BIOS could be ok. The eeprom is soldered on, making it long and difficult 😀

It is alive, that's already a big relief.

Okay, so ran memtest86 again. Ran for maybe an hour or more...and I noticed it wasn't progressing. Rebooted and it's back to it's non responsive state. Diag board just shows dashes and no response at all.

Keyboard does light up briefly on startup.

I have not tried anything else yet, this is just after noticing it suddenly wanted to power up. I don't see anything obviously wrong with the board or obvious scratches, etc. Will have to look when I have time again.

Based on what you're saying, sounds like it could be a cracked solder joint somewhere, i.e. when the board is cold it "works" but then after it warms/heats up it starts failing probably due to expansion of components.

pan069 wrote on 2025-01-12, 20:38:

Based on what you're saying, sounds like it could be a cracked solder joint somewhere, i.e. when the board is cold it "works" but then after it warms/heats up it starts failing probably due to expansion of components.

Yeah, after it wouldn't boot several times, I gently pushed on opposite corners and suddenly it decided it would boot again. Does that sound more like cold solder joint or a bad trace somewhere? Any suggestions on where to focus based on symptoms?

Sometimes my PC diagnostic card wouldn't even show the dashes, it showed absolutely nothing at least once that I saw.

Would probably try dip chips first and other through hole parts since they would be easiest to try without a ton of effort on the surface mount 😀.

Alright, I resoldered many of the through hole parts the other day...and the board seemed good running memtest 86 for about 4 hours.

So then I decided to gently push on the board again some to see if it would act up again. And unfortunately it did (memtest86 suddenly would get an error and lock up). My PC analyzer card was indicating the last codes were 12 and 13. I'm not sure if that means it started test 13, or completed 13. But according to the manual PC analyzer manual (if it's correct):
13 = The video display has been disabled, Port B has been initialized. Next, initializing the chipset
14 = 8254 timer test will begin

So not sure if that means it failed during 14, or during 13.

Playing around a little, I determined that pushing on the 74F373 chip (next to the cache chips) was enough to get it booting again. Doesn't mean that's the chip since the whole board moves a little when I pushed on it though.

It was odd that this time when it was failing it would keep stopping at 14, whereas previous it wouldn't even start any of the BIOS routines.

The hunt continues...

Loose solder/chip somewhere. Maybe the one you're pressing, maybe one that flexes when you press it.

myne wrote on 2025-01-16, 01:56:

Loose solder/chip somewhere. Maybe the one you're pressing, maybe one that flexes when you press it.

So should he bake it ?

30yo capacitors don't take too kindly to baking

If they're going to replace all the electrolytics, sure.
I'd just reflow everything from behind.

Good low clean flux, and about an hour to touch every pad

Haven't seen any electrolytics on this board, just tantalums and MLCCs.

Any recommendation for a low clean flux? I use Kester 186 and it's always a bit of work to clean up.

Not really. I just bought random stuff off ebay