It's difficult to say for sure. Maybe ESCD has wrong data. Does the BIOS settings have a menu item to clear or reset ESCD ?

Not sure if it's the same in your case, but I've had some motherboards freeze when accessing the CMOS setup because:
- one or more modern low RPM fans were connected to the motherboard's fan connectors. If there's a BIOS bug, it doesn't know how to interpret the RPM reading (or it interprets it as Schrödinger's Fan - which is both off and on at the same time 😁 ), and it simply freezes. The solution was to use molex adapters and connect these fans directly to the PSU.
- PSU was missing the -5V rail. Again, certain BIOS versions might have a bug and freeze if the returned -5V value is null.

Either way, what you want to do in these cases is strip the system down to the bare minimum and go from there. It also helps to test other parts (if you've got different RAM modules, video cards, etc).

Roman555 wrote on 2022-12-29, 10:54:

It's difficult to say for sure. Maybe ESCD has wrong data. Does the BIOS settings have a menu item to clear or reset ESCD ?

don't think there is such an option. could try auto config w/ optimal or fail safe settings, but i would have thought that taking out the battery would reset those ESCD settings as well upon restart...

- one or more modern low RPM fans were connected to the motherboard's fan connectors. If there's a BIOS bug, it doesn't know how to interpret the RPM reading (or it interprets it as Schrödinger's Fan - which is both off and on at the same time 😁 ), and it simply freezes. The solution was to use molex adapters and connect these fans directly to the PSU.

yeah, i'm aware of that problem (though have just seen it as pausing on post with a warning) and always hook up fans only via molex now.

- PSU was missing the -5V rail. Again, certain BIOS versions might have a bug and freeze if the returned -5V value is null.

PSU does have -5V, moreover it did work fine not that long ago with this PSU. i'll try another CPU later, though that would be weird given that win98+games all work fine.

i usually just store these boards in antistatic bags while keeping the battery in, could that be a bad practice that leads to stuff like this? though on second thought, isn't that how new mobos are packaged anyway...

the fail safe settings do allow entering the bios again without a freeze, so now to figure out what setting exactly causes this. the optimal settings mostly seem to correspond to what is set after clearing CMOS. there also is in fact a "reset NVRAM" option, but enabling that did not help the lockups.

i did already verify through datasheets that the memory can run the fastest timings at 66mhz, and it still locked up with slowest timings set, so at least that can be ruled out.

well, i couldn't figure out the cause of this. i went ahead and loaded the fail safe settings, then set the optimal settings one by one and was able to get into bios after a reboot. but loading the optimal settings via the bios option will still cause the lockup.

post screen says "A6117MS V1.8 082198". i could probably dump this bios if someone is interested in that (preferably with a note what the bios chip is though, rather would not have to peel the sticker off).