damianmcmillan wrote on 2021-09-28, 15:38:

Hello! […]
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Hello!

I have a Dell Optiplex 466, which upon booting today, presented me with a screen saying:

"SYSTEM BIOS IS DAMAGED. RELOADING FROM DISKETTE IN DRIVE A"

The floppy drive seeks, but no matter what I load onto the floppy, the machine does not boot, nor recover the BIOS.

I can see it is reading tracks on the floppy - track 50, track 08, track 00, but always ends with A:00 and nothing further.

I have tried making a 1.44 blank disk, and putting these files (one file per try):
4XXL_A17.HEX
4XXL_A17.ROM
4xxL_A17.exe

Does anyone have any idea how to actually have the BIOS read the appropriate image from the disk?

You could try clearing the CMOS -- maybe it has a bad checksum and clearing the memory would let it boot? It's not impossible for ROM chips to die but IMO that usually is the result of corrosion or static. Might be worth a peek in the machine to make sure the battery hasn't leaked...

There are no DIP switches to reset the CMOS settings - if I remove the battery (it's an old 4.5v external type - it hasn't leaked) then the CMOS settings are usually cleared.

I have left the battery disconnected, and the mains cable disconnected for some time (30m-1hr) which would 100% in the past have wiped the CMOS (i.e. it would warn of a RAM size mismatch, I would need to reset time/date etc) to no avail.

Tomorrow I will try desoldering the flash IC (an Intel N28F001BX-T150) and reprogramming it - I suspect this may be the only way - there is absolutely no information about the correct format of the recovery disk/floppy online.

Some motherboards have a small button somewhere which allows you to reset the CMOS...