BIOS ROM might as well be corrupted due to a former failed attempt to flash it or because someone shorted pins or whatever.
I would first try a complete clean reflash of the current EEPROM (including boot block) in a similar board and see if this fixes the error.
The Dallas clock needs to be "modded" or better replaced. These are still being produced and available.

Yeah, try to reflash it before you buy a new ROM.

Looks like the BIOS ROM is corrupted, so ordered a few replacements from eBay.

Tried to reflash it with uniflash 1.40, it fails.

Waiting for programmer as well, as secondary bios flashing option.

Aha ! So yeah this proves that BIOS ROMs sometimes just fail.
Now I don't know if it's just bad luck or if this could become a trend in the upcoming years ... I've had this happening to me twice so far. This is an uncommon failure, but it's not impossible either.

Wondering where I can find NOS or new EEPROM DIP32 replacement for this particular chip which is the failed one:

FLASH P28F001
BXT150

Uniflash 1.40 recognises it as

Flash ROM chip: Intel 28F001BX/BN-T/12V
Organisation: sectored 1x112k,2x4k,1x8k (128K)

Especially if this chip in particular is prone to such failures, replacement with new ones and not used old ones would be preferable.

finaly, light at the end of the tunnel... and HOT-541 is ALIVE!!!! with EEPROM replacement and BIOS chip programmer, as hot flashing failed.

the long story :

1. when I got the motherboard, it turns out it had the wrong BIOS version (and I didn't know it back then), so at boot time it did show a BIOS checksum error. But no way to access BIOS setup, did not see any HDD, just floppy drive to boot DOS, so kinda useless...

2. because it has an INTEL EEPROM chip, and reading the README file provided with BIOS versions (10, 13 and 20), I understood that for INTEL EEPROM I have to use only version 10 of the BIOS. So I flashed it, but ain't I lucky? BIOS chip failed during flashing process (age? quality?) and got flashing error.

3. Result? a bricked motherboard 🙁

4. few attempts to hot flash the BIOS using another socket 7 mobo did reveal INTEL EEPROM chip had errors - so ordered replacement ones - same make and serial, not NOS, but used

5. replacements arrived last week, hot flashing failed again using uniflash 🙁
still wondering why (mobo supports only 5V flashing default option, guess INTEL P28F001 EEPROM needs 12V?), as with programmer, it worked flawlessly... maybe using a board with 12V jumper for flashing the BIOS would have helped with hot flashing, might try it at some stage.

6. EEPROM programmer arrived today, flashed version 10 of BIOS and... progress, but stuck back at step 1.

7. then, I decided to use one of the BIOS versions (13, or 20) not recommended for INTEL EEPROM - and surpise! it works, full access to BIOS setup, HDD is seen and boots from it. 😀

Only issue left is to hack the DALLAS RTC or desolder it, put a socket instead and add new /re-use hacked RTC module. Maybe a CACHE module as well to maximise performance of this motherboard (not really needed for now, but just in case)

Thank you @deksor @horun @majestyk for guidance and suggestions, now my Intel Pentium 75 is running DOOM and QUAKE (demos) at full speed 😀

Good to see a happy ending to all of this 😁

Enjoy your Pentium system 😀

Deksor wrote on 2021-03-01, 23:01:

Thanks for making that photo by the way. I added it here http://www.win3x.org/uh19/motherboard/show/4448

I've updated some info on the site. Two identical & working machines I got a few weeks back have HOT-541 in them, both with P120s and the max cacheable ram (2*32 MB).

Good to see another brought back from the dead!