A couple of those HT12 boards on TRW are mine.

Most HT12 boards use a split odd/even bios, so you have to programme a pair of them. Fortunately most HT12 bios images will work on most HT12 boards.

The difference tends to be minor, most offer some combination of hardware EMS enablement, shadow functions, fast wait states or some combination of them. Try different ones until you find one with the combination you want. The Eurosoft bios on TRW is from my board, I found it unusual in that it was a UK company who wrote it - an oddity in the world of AMI and Award.

When I get this board situation was worser because there is no stickers on BIOS chips (HI and LO) and I think that they were in wrong sockets, board don't wanted to start at all. After changing their positions now I heve situation like I wrote in my first post. Maybe it is possible to replace these EPROMs with EEPROMs? These 27C256 need higher voltage for programming and I know that my Willem have a problem with this. I need better programmer or some EEPROMs but which type should I buy (if it is possible)?

🤣, I'm currently trying to repair this motherboard.

Before I had reset working I had 01 to 09 codes displaying. Bios chips weren't the correct ones. I can't test any bios as it only displays -- -- due to a missing 8MHz signal.
Now I don't have anymore activity.

Do you mind if I ask a few measurements?

Yes, as long as you get eeproms that are pin compatible with the original chips they should work fine.

Winbond W27E257 should be equivalent to the old 27c256, but electrically erasable. But please check th pinot first.

megatron-uk wrote on 2023-11-17, 20:54:

Yes, as long as you get eeproms that are pin compatible with the original chips they should work fine.

Winbond W27E257 should be equivalent to the old 27c256, but electrically erasable. But please check th pinot first.

Pinout is the same

https://pdf1.alldatasheet.com/datasheet-pdf/v … ND/W27E257.html
https://pdf1.alldatasheet.com/datasheet-pdf/v … S/M27C256B.html

I've got a ht12 286 12mhz around here somewhere and I remember it can't have the onboard ram chips installed at the same time as the 30 pin Simms pm me if you need something from it

My chips are Microchip 27C256 without window to erase - it is imposible to erase these chips?
I just checked that when I try to reset my board I see light on diode reset on my POST card but nothing is happening - POST codes are not starting from the beginning.
In one of documentations on The Retro Web there is information that if You use memory modules, You can not use memory chips in sockets.

Tomek TRV wrote on 2023-11-17, 22:58:

My chips are Microchip 27C256 without window to erase - it is imposible to erase these chips?
I just checked that when I try to reset my board I see light on diode reset on my POST card but nothing is happening - POST codes are not starting from the beginning.
In one of documentations on The Retro Web there is information that if You use memory modules, You can not use memory chips in sockets.

You should be seeing codes on POST card, even if ram is an issue.