Every flashing tool I know does basic checks before actually flashing. That is, BIOS string, checksum, etc. Also, they almost all ask if you want to backup the current BIOS first. So not that much can go wrong. However, if the BIOS is ok but completely wrong for the mainboard, you may not be able to boot from floppy again to flash the backup.

Alright, glad to learn that. I guess I'll try AWDFlash and see how it goes.

Any idea if I can boot from a CD after such a failure? I don't have any floppies that still work properly but I can boot into DOS using Win98's CD and FreeDOS 1.2.

You should look into getting a cheap programmer like the TL866. I don't even bother using flashing programs anymore. Just pop out the chip, stuff it in the programmer, flash the .bin, done. And no more worrying about anything going wrong. Flashed the wrong file? Just do it again with the correct one, all that happened is you lost two minutes.

Tbh, I'd just grab a second EEPROM and hot-flash it, so you don't have to touch the current one, as old EEPROMs that still read fine can die from the higher voltages used when flashing.

So:
- get another EEPROM with same capacity (256kB/2Mb)
- copy the image and uniflash.exe (v1.40) to a reliable medium (HDD) that is bootable with DOS
- with the motherboard off (no power!), loosen the current BIOS EEPROM so it can be easily removed
- boot the motherboard into DOS
- while the system is running, remove the current EEPROM and put the new one in (be sure to get the orientation right)
- flash the new image onto the new EEPROM

You don't even need to do this on the same board, in fact if it's particularly rare that's a good idea. This way you still have the original BIOS EEPROM untouched and available no matter what the new file is/does. Regardless, it is of course a good idea to read the old one and back it up (i.e. to vogonsdrivers)

Hot flashing works, but it's dangerous and you need two Flash-ROMs of exactly the same type. Another, better option if you don't want to spend money is to use an ethernet card. You can flash 256kB Flash-ROMs using an RTL8139 card.

dosgamer wrote:

You should look into getting a cheap programmer like the TL866.
I don't even bother using flashing programs anymore. Just pop out the chip, stuff it in the programmer, flash the .bin, done.
And no more worrying about anything going wrong. Flashed the wrong file? Just do it again with the correct one, all that happened is you lost two minutes.

I second that. Saved me a lot of headache when I flashed a Geforce 2 MX for my Mac.
The only exception are some weird BIOSes from Delll. The Optiplex series, for example, uses an encrypted BIOS.

The flasher writes some license stuff into it (key for OEM Windows ?), so I can use neither my TL866, nor my G540.
Speaking of the Optiplex, I enountered a weird issue that I got fixed with a BIOS update (2011 release or newer):

Previously, it would freeze after a short amount of time after I entered in the CMOS setup.
It also would reset after some random times when Windows is active.
Sometimes, it refused to power-up, even (had to clear CMOS via jumper each time, to make it POST again).

This was among the strangest things I've ever experienced on a PC. 😁

dosgamer wrote:

Hot flashing works, but it's dangerous and you need two Flash-ROMs of exactly the same type.

No you don't. Anything that the board you are flashing on that is supported by your flash software (in the case of Uniflash: almost anything) will work.

And dangerous? I have two left hands (you don't want to see what happens when I try to repair my vintage motorbike myself...) and have been hot flashing for ~20 years and even I've not once fried a board - and the one EEPROM I killed was due to incorrect orientation, which would be just as deadly if you flashed on something else and then inserted in the board.

Another, better option if you don't want to spend money is to use an ethernet card. You can flash 256kB Flash-ROMs using an RTL8139 card.

Hmm, worth a try, have tons of those no one wants to buy or even take for free 😉