Should be readable by selecting a generic 27C512-type device.

^ yep , 27C512 is the way to go
does the silkscreen under the chip say anything? or something near that area? sometimes there is a 27256 or 27512 or something similar under it - should be a strong hint 😉

Sweet will give it a go 😀

EDIT: That seemed to have worked. I will test the dump when some spare BIOS chips arrive from eBay.

My 486 has a 27C1024 in it. I would suggest reading it as that just to see if the buffer is filled up.
Obviously if it's only half filled it's a 27C512

Imperious wrote:

My 486 has a 27C1024 in it. I would suggest reading it as that just to see if the buffer is filled up.
Obviously if it's only half filled it's a 27C512

Great idea! Will do when I get home.

The buffer will fill up with duplicate data, at least that's the case with both tl866 and gq-3x programmer software , so if the chip for example is a 27512 and you chose to read as 271024 you'll end up with a 1024 buffer with 2x of the same data.
In this case Phil's rom is a 28pin device - 27C1024s are 40pin devices so the max here is 27C512

Ok, cool. I'll go back to plan A and when the replacement BIOS chips arrive, will flash it and see if the bord works 😀

Have you tried NSSI's BIOS saving utility (provided you are able to boot up with the motherboard into DOS)?
I've managed to save a number of BIOSes that way - not sure whether it worked, but it did produce output files equivalent to the size I would expect.

jesolo wrote:

Have you tried NSSI's BIOS saving utility (provided you are able to boot up with the motherboard into DOS)?
I've managed to save a number of BIOSes that way - not sure whether it worked, but it did produce output files equivalent to the size I would expect.

Yes, I got dumps both way. Will test them both when the blank chips arrive.

PhilsComputerLab wrote:

jesolo wrote:

Have you tried NSSI's BIOS saving utility (provided you are able to boot up with the motherboard into DOS)?
I've managed to save a number of BIOSes that way - not sure whether it worked, but it did produce output files equivalent to the size I would expect.

Yes, I got dumps both way. Will test them both when the blank chips arrive.

Excellent. I've also got some chips and a burner on the way.
I'm eager to find out if it works, since it then saves you the trouble of physically removing the BIOS chip (my gut tells me it will).

keropi wrote:

The buffer will fill up with duplicate data, at least that's the case with both tl866 and gq-3x programmer software , so if the chip for example is a 27512 and you chose to read as 271024 you'll end up with a 1024 buffer with 2x of the same data.
In this case Phil's rom is a 28pin device - 27C1024s are 40pin devices so the max here is 27C512

You are 100% correct there, my bad.

I was probably meaning 27C010 eprom, but even that is 32 pin. The eprom in my 486 is actually mis-labeled 27C1024 but is a 27C010.

heh yeah they used to put fake/clone/cheap eproms in older mobos to save money... 🤣 🤣 🤣