Without system BIOS, the computer has no way to know how to boot from a floppy.

You'll need to hotflash the chip in another board.

Oh yeah, hotflashing an EPROM...

Wow, a Harris 286-25!

This thing definitely needs to be resurrected - if you don't have anything else capable of flashing a 27512 / 27c512 then I'd reccomend you invest in an eeprom programmer. They're really useful pieces of kit for retro pc/gaming use.

iulianv wrote:

As you can see, the BIOS chip is missing - now, there was this "urban legend" about newer (AGP/PCI) mainboards, that if you have an ISA slot and an ISA video card available you can always recover from a bad BIOS flash by trying again, because FDD booting and ISA video output don't require a good BIOS.

It is said that it should work because the first blocks of the BIOS can boot from floppy. In that case, you could build a bootable floppy with your flash program, your BIOS and AUTOEXEC.BAT with instructions for flashing the bios from command line.

Note that it applies to BIOS partially flashed (and only if the first blocks are OK), not to completely missing or erased BIOS. Also, I don't know if a video card is required at all.

In your case, you should program the BIOS inside an EPROM chip and put it in the socket.

Since you have done the hard part - located the BIOS file, it shouldn't be too hard to get it on a chip.

You can buy a 28F512 or 29F512 chip which is erasable and compatible with the 27512 EPROM.
You can either try and hotflash in a working board (i.e. pull the good BIOS chip out, put in the blank chip, run UNIFLASH or similar to program the 286 board's BIOS, then shut down and try the newly programmed chip in your 286).
Alternatively you might be able to flash it using a network card with a bootrom socket, using UNIFLASH.

Finally if you've no luck you can buy a USB programmer off ebay, like the G540 which I have and can recommend.

I see that both 28F512 and 29F512 are 32-pin (socket on the board is DIP-28)... however I should be able to locate people around here that offer such services (PROM programming).

Next step would be finding a 287-16 (or maybe a 20MHz oscillator, since I already have an AMD 287-10)...

Hmm, I have two more (potentially dumb 😁) questions:

- if I take a BIOS chip from some other working board (386 or 486) and put it on this one, should I have video output? errors, gibberish, anything...

- if I find a spare 28-pin flash PROM, but bigger (let's say 1Mbit), is there any chance for me to UNIFLASH the 512Kbit BIOS image on it, and use it with this board?

BIOSes are mainboard dependent, let alone CPU dependent.

Doubt you will find a 28-pin chip with more than 512Kbit.

So, even if it doesn't output anything with a foreign BIOS (which it doesn't - I just tried it with an AMI BIOS taken from a 386SX board), there's still a chance that my 286 board isn't toast... that's good news 😀.