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 😀
Retro builds & sandbox
IBM XT 5160 | 286 | 386 | 486 | S4 SI5PI AIO & S4 Batman + P60 SX828
S8 & PPro 200 | SS7 FW 5VGF & Asus P5A & AOpen AX59PRO K6-III+ 550MHz
Asus K7M Athlon 1Ghz GDF | Abit SH6 Pentium III 1GHz SL4KL...