weedeewee wrote on 2022-07-09, 19:04:

GigAHerZ wrote on 2022-05-26, 17:44:

chrismeyer6 wrote on 2022-05-26, 15:57:

Silly question is the bios battery good and have you tried a clear cmos?

Battery is good, it does hold the voltage well enough that it shouldn't be a problem. (2,7V, while rated at 3V)
I did try to clean the cmos - no effect.

FYI, 2.7V is close to empty for a button cell. Though I'm guessing that an empty battery likely isn't your problem.

I've had a ton of motherboards either not post or act weirdly with a dead/low/missing battery. I would totally start with putting a fresh battery in it and see what happens.

chrismeyer6 wrote on 2022-07-09, 19:26:

weedeewee wrote on 2022-07-09, 19:04:

GigAHerZ wrote on 2022-05-26, 17:44:

Battery is good, it does hold the voltage well enough that it shouldn't be a problem. (2,7V, while rated at 3V)
I did try to clean the cmos - no effect.

FYI, 2.7V is close to empty for a button cell. Though I'm guessing that an empty battery likely isn't your problem.

I've had a ton of motherboards either not post or act weirdly with a dead/low/missing battery. I would totally start with putting a fresh battery in it and see what happens.

Okay, it now has coin cell battery holder and a fresh battery. Unfortunately the behavior did not change. 🙁

GigAHerZ wrote on 2022-07-09, 18:19:

The debug card doesn't show anything and didn't show anything before desoldering either. I'm afraid it was a hiccup of the debug card itself earlier.

then desoldering ram was fools errand 🙁
you could modify your post card to decode Port 84

>salea logic analyzer clone

16 channel one? with 16 channel one (or FX2 development board as it also exposes all 16 pins) you could catch post codes directly from ISA bus

The problem can be from anywhere else than oscillators. Compaq generally used 4 legged black ones. I have mistakenly dropped one tiny leaf of cable between two legs inside my Compaq Deskpro 4/66i at year 2002 mistakenly. I open the unit, the room filled with black dust! The board run into fire! I immediately close it, but there were a 2 mm burned black hole at one of the legs on 16 MHz oscillator chip. Do not deal with oscillators, they are extremely dangerous!

At eBay there are spare Compaq mainboards are selling, if you are lucky try to find a compatible one for your case. If your power supply is fine, mine was a 145 Watt unit it can work, after the mainboard replacement. But before that, generally speaking Compaq mainboards have 4 or 8 MB onboard rams. Remove all additional ram modules if you have and try to power up the unit. If no cure, think for a replacement.... but, if the fault is at your PSU, it will not open again. Do you have a spare CPU to test? Try the older one too.