Silly idea but try a cmos fresh battery. The other thought is does the problematic board have any bad capacitors?

I've tried clearing the CMOS and have a fresh battery installed ,and looking at the capacitors on the board, they visually all look ok.

Well another thought is corrupted or a bad bios. If that is the case as was with my first pc. It's not an easy fix. You would need to be able to flash or replace the bios rom.

with a fresh battery the date and time part should go away.
try removing and reinstalling the ram, and/or try the memory one at a time if you have more than one module.
that bios has either been reflashed, or the computer was sold very late. a P15 bios with a 98 date? p2 was out beginning in 97.

If it is the BIOS then Intel boards usually have bios recovery option which you can use if the main BIOS gets wrong. Check the manual.

There is ONE jumper on the board that has 3 positions, 1-2, 2-3 and OFF alltogether (so take it out). If you take it out and power on the board it will try a recovery bios from floppy that should contain the bios update for that particular board.

Thanks for all of the advice! My suspicion has also been that somehow the BIOS has been corrupted, but this would the first time in almost 30 years working with computers that I've seen that so I didn't want to jump to conclusions. Looking at the manual, there is indeed a BIOS recovery option. Now I just need to track down a valid BIOS and try to flash it this evening. Thanks again!

Found one here. Even Intel is not offering them anymore for boards of this era.
http://www1.medion.de/downloads/index.pl?op=d … treiber&lang=uk

Fantastic! I'll give it a shot tonight.

I was able to successfully flash the BIOS via recovery mode, clear the CMOS, and it's still not really working. Unlike the previous BIOS that froze so hard during boot that not even the keyboard status lights would change, the keyboard status lights update when caps lock, num lock, or scroll lock are pressed. Additionally, while the previous BIOS would boot with a USB keyboard plugged in, this one will not.

The K6 200 CPU gets a bit further.

NickJ80 wrote on 2020-10-02, 01:36:

..Additionally, while the previous BIOS would boot with a USB keyboard plugged in, this one will not.

Is that even with USB legacy set to 'enabled' in the BIOS? - from P08 omward the default value was set to 'disabled'

Unfortunately, I cant even get into the BIOS config. The system locks up before I'm able to.

Sadly, I haven't made any more progress with this motherboard. I'll probably try to track down other BIOS revisions to try, but I'm not hopeful. I'll likely have to abandon this particular board. I'm open to other ideas if anyone has any. Thanks again to everyone.

NickJ80 wrote on 2020-10-03, 16:38:

Sadly, I haven't made any more progress with this motherboard. I'll probably try to track down other BIOS revisions to try, but I'm not hopeful. I'll likely have to abandon this particular board. I'm open to other ideas if anyone has any. Thanks again to everyone.

There's a good selection, upto & including P10, here

http://cwcyrix.duckdns.org/intel-legacy-files … 20AN430TX/BIOS/

and a copy of the full bios history

That's a great help. Thanks.

Could you try disabling onboard cache?
I've had similar problems with defective cache chips before.

Do you have a multimeter?
I would try measuring voltages if you can (while the system is trying to run). Low voltage somewhere could cause problems like this.
I'm not suggesting you swap PSUs, I'm wondering if you can verify that the voltages are actually good when using this board.

I've tried several different BIOSs at this point, with no real improvement.

Regarding disabling the onboard cache, the board does not provider jumpers to disable it. The cache can only be disabled in the BIOS, but the system freezes before I'm able to enter the BIOS.

As for a multimeter, I do have one, but I'll admit that I'm really a novice when using it. I've used it to test continuity and voltage levels coming directly from power supplies, but not much more. I'm not really sure what to test directly on the board itself, but I can poke around a bit and see if things look somewhat sane.

Thanks for the suggestions.