I've had this happen to me once and I "hot flashed" it, but I'm not sure it it'll work with this type of chip. If you have a board that takes this form factor, power it up like normal, get to a DOS Prompt and have uniflash at the ready. While the system is running, remove the BIOS chip and replace it with the one that has the bad flash. Run uniflash and program the latest BIOS (or the original if you backed it up) and you should be good to go.
Now, granted, I've not tried this method on this sort of BIOS chip, I've only ever used it on the more common 32pin chips. You might also need to be delicate with your moves as you can get the system to hang rather easily. Hope this helps!

I've got the same m/b so let me know if you need anything.
Although my knowledge starts and stops at flashing bios's with official ones supplied by the manufacture.
(and luckily never had to recover from one)

I did a hotflash some days ago, it was a 32 pin chip and I had a similar problem with award flash, I had to try different versions of awdflash until one recognized the chip and flashed it.
So my suggestion is to try with the flash utility of the working board and different versions.

I tried it in the MSI K7N420 with Uniflash too now and that also said the flash chip is unknown. But it recognized the board's original flash chip ok. I also tried a couple of Award Flash versions for the K7N420 and flash chip again unknown. It also complained that the SD11 BIOS file on disk is not Award though.

This Winbond chip is on the supported list for both Uniflash and FlashROM, so I'm thinking the flash chip has died for some reason... Going to get a replacement chip.

I'm afraid you are correct and the flash chip is dead 🙁 .
The only time this has ever happened to me was with a 440BX board that had a Silicon Image ATA66 controller on board and the chip had a different bank for the controller BIOS. Trying to update to the latest BIOS bricked it and no matter what I did, I could never properly flash it, even with an external flasher. Had to source a similar flash chip and then it worked fine 😀.

I think another problem I have is the SD11 BIOS chip W29C020CP90B is a 5v chip whereas the other two boards I have with sockets are using 3.3v chips.

Should I get a PLCC32 To DIP 32 adapter? I could try flashing on an older board then.

Or Chinny22 would you like to hot flash a chip on your SD11? 😀

No problem doing it, would need to get a chip and extractor tool first. Plus the whole UK to US shipping.

piatd may be closer he's got the same M/B
Re: Bought these (retro) hardware today

But yeh if I'm your best option I've no problem getting the bits and posting it over

chinny22 wrote on 2020-08-04, 16:37:

No problem doing it, would need to get a chip and extractor tool first. Plus the whole UK to US shipping. […]
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No problem doing it, would need to get a chip and extractor tool first. Plus the whole UK to US shipping.

piatd may be closer he's got the same M/B
Re: Bought these (retro) hardware today

But yeh if I'm your best option I've no problem getting the bits and posting it over

Oh I thought you were in the USA for some reason. Yeah I'd probably be better off buying another motherboard instead of us shipping stuff around, plus risking your hardware.

I am going to try a new chip and adapter. I have some other boards with socketed 5v eeproms. This is actually a rather interesting little debacle.

I got it working again. I noticed that immediately upon power on there was floppy drive activity with the dead BIOS. It occurred to me this might be a bootblock BIOS recovery mechanism. The procedure for recovery with an AMI BIOS is a floppy with the BIOS file renamed to AMIBOOT.ROM. And so the board came back to life about 30 seconds after power on. Sweet!

I haven't a clue what their DOS flashing utility did wrong, but kudos to the bootblock.