From this picture: https://www.google.com/search?q=Tyan+S1856S+T … =Zi1ykbCbbEPJZM it' should be a Winbond chip. Any 2 Mbit(256x8) flash ic in a dip32 package should work like: https://pdf1.alldatasheet.com/datasheet-pdf/v … 9F002UP12B.html, https://pdf1.alldatasheet.com/datasheet-pdf/v … 002NT-55JC.html or http://www.datasheet39.com/PDF/543905/F29C510 … -datasheet.html and there are many others. Check on your spare parts/defective boards, if you have any, for a similar ic. Mind the pinout/key !

Yeah, original BIOS chip is a Winbond W29c020 IC. Theoretically, any 29C variant chip would work on this board.

https://pdf1.alldatasheet.com/datasheet-pdf/v … D/W29C020C.html

I hope you get that working. I love Tyan motherboards.

Thanks, i know which one I'm gonna search for now 😀

It would be a pity if this one would be recycled just because of the missing bios, it's a nice board indeed!

I was lucky enough to pick up a Tyan S1854 as part of a lot I purchased for $50.00. When it didn't POST, I took the BIOS chip out and reflashed it in my programmer and it worked fine - I guess maybe it had a bad BIOS flash and ended up being stowed away.

Little update after a year.
The board has been laying in a box, stored away because of other projects.
I got a 29c020 chip and used uniflash om another board to hotflash the most recent bios. Uniflash succeeded, the other board sort of tried to boot with it (semi-success because of wrong bios for the board).
Placed the fresh-fladhed chip into the Tyan, put a celly 733 and some ram in (jumpers to celly 433), and turn it on.
Nothing.

Post card gives me ---- and ready signal status off.
I'm lost for now 🙁

waterbeesje wrote on 2024-05-10, 22:20:

Little update after a year. The board has been laying in a box, stored away because of other projects. I got a 29c020 chip and u […]
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Little update after a year.
The board has been laying in a box, stored away because of other projects.
I got a 29c020 chip and used uniflash om another board to hotflash the most recent bios. Uniflash succeeded, the other board sort of tried to boot with it (semi-success because of wrong bios for the board).
Placed the fresh-fladhed chip into the Tyan, put a celly 733 and some ram in (jumpers to celly 433), and turn it on.
Nothing.

Post card gives me ---- and ready signal status off.
I'm lost for now 🙁

Maybe PPGA only...Tyans cpu matrix shows no FC-PGA support for the board

Maybe, thats something to put on the list 😀
I think I have a 433 or 400 Mendocino in the box to try.

Just read the manual and it shows Celeron compatibility only, while theretroweb states it supports coppermine as well, so that's why I've put in the 733.
Yes I know the garbage collection from good old th99 still remains and we all are fixing and updating TRW and support may vary from board to board 😉

It's a workey!
I've put in the Mendocino 433 and it boots right to the CF card.
Mission accomplished!