I have an MB-8500TUR which is a similar board. I had issues with it not posting until I cleaned dust off the pins on the QFP chips and other surface mount chips as it was quite dusty.
In addition to cleaning with compressed air, make sure you've tried disconnecting the hard drive, floppy drive, and CD-ROM drive ribbon cables, and removed cards other than the video card, in case it is some device other than the motherboard causing it to hang up.

jakethompson1 wrote on 2025-10-01, 18:40:

I have an MB-8500TUR which is a similar board. I had issues with it not posting until I cleaned dust off the pins on the QFP chips and other surface mount chips as it was quite dusty.
In addition to cleaning with compressed air, make sure you've tried disconnecting the hard drive, floppy drive, and CD-ROM drive ribbon cables, and removed cards other than the video card, in case it is some device other than the motherboard causing it to hang up.

The board was already clean enough, but I've made sure there is absolutely no dust on the QFP chips and other chips (and i've also checked for lifted pins since i've heard it can be an issue)
My current setup is just the ram, the COAST cache (i've tried without and it made no difference), and the video card on the same slot it used to be (i've tried others with no change)
One thing i've forgot to mention is that i've also added a coin cell battery holder (and a new battery) to the HT12888A RTC just in case since I've heard it can contribute to boot failure

I see. ISA POST card would be the next step. You should get some codes if it's able to beep with no RAM.

jakethompson1 wrote on 2025-10-01, 19:31:

I see. ISA POST card would be the next step. You should get some codes if it's able to beep with no RAM.

I'm thinking of getting a PCI/ISA POST card. If i plug in the PCI side will it work on such an old motherboard? I know this may sound stupid but I've heard it's possible to fry your pc if you plug in the ISA slot backwards and I don't wanna run any risks.

The POST card has arrived. It stops at code C6, which is a cache related error. There are 2 10uF electrolytic capacitors which i've tested and their ESR is a bit on the high side (0.9ohms). I do not have new replacements at the moment so I've tried with some salvaged caps (0.5ohms ESR). The problem still persists. Is the ESR of the caps ive tried too high? Or what else could be wrong?
Thanks.

I've checked the CPU voltage (that according to the jumper should be 2.8v), but it's actually 3.5v (the maximum setting). The LM431 doesn't seem to be responsible, so the NEC D2583 are probably the culprits. I know the CPU is most likely permanently damaged, but I still want to attempt a motherboard repair. What are some modern alternatives to the NEC D2583?
Thanks.

What RAM are you using? And you already replaced the Dallas chip with a fresh one?

The absolute max voltage specified for a P-233 (on VCC2, lowest specified voltage) is 3.7v. So what ever CPU you're using should be fine.

Electrolytic capacitors are bad for ESR in general.

Is there a jumper or bios setting enabled for the COAST cache that expects the right stick even though nothing is inserted? Does a BIOS clear with no COAST stick do anything?

Did it work before modifying the HT12888A RTC?

Do you know all the components (RAM, video card, CPU) work in another motherboard?