jmarsh wrote on 2024-06-23, 14:54:

NHVintage wrote on 2024-06-23, 13:37:

I'm not so sure here - check this article out - its for a different system but the same chips are involved. I got a pair of 27256's on the way today from Amazon - if the storms don't cancel the delivery or keep me from going out to get them - so I guess we'll see:
https://electronics.stackexchange.com/questio … -how-to-wire-we

I'd assumed that you would have taken that into account already...
Bend pin 1 of the 28C256 upwards so it doesn't go into the socket, connect a wire from it to pin 27 (which still should go into the socket). A14 will be driven correctly and WE# occasionally being driven low won't matter - there's a command sequence required to enable programming and it will be impossible to be fed to the chip in that configuration.

I got the chips - which were labelled as ST/Thomson M27C256B but whose ID on the burner was for Fairchild FM27C256 - and that solved the 256 Trangg Bow's issue, it booted to BIOS and I was able to get into the CMOS settings. It has a Holtek multi-IO board (because it doesn't have its own IDE or FDD interfaces) and I was able to configure the SD-IDE; it then returned a 'no operating system' command, which tells me that it sees the SD card which is currently blank. Yay! I'll have to update theretroweb for that board to add the BIOS I found from one of the regular contributors here and there.

So that just leaves the 386 DTI SBC and it not seeing FDDs or the SDIDE card there. I have the blank chips for that board so I am thinking of flashing a more useful BIOS onto that one, we'll see.

Spoke too soon! The BIOS seemed to work, but in fact it wasn't seeing the extended 4MB RAM on the board, just the base 640k. A second BIOS which turned out to be just another version number of the same AMI BIOS acted the same way. I learned from another server that W27e257 are direct replacements, so I have ordered some, but in the meantime I've jury rigged a UV box using a 3W sanitizer light to erase the 4 27256 Eproms I have. Give it 30 min and I guess we'll see how well the box works. 😁

And another update: I installed a NIC card with IDE-XT BIOS on the 386 SBC machine and it succesfully searched for hard drives, but didn't see them... but I replaced the Winbond multi-io board with a Holtek one and the problems with the SD-IDE drive and Flashfloppy disappeared. Thanks to someone on one of the other boards for helping me figure out how to program the XTIDE BIOS on the chips I had on hand. So this machine is booting, and I've installed a sound card and vid card and it's in pretty good shape (if a bit low on memory, but I have to try some things first with extended memory managers etc). I AM having a problem with its USB-ISA card outputting gobbledygook not readable directory listings, but I've seen that before on other machines and its problem for another thread.

I'll need to get a new multi-io board for the 286 machine and I'm awaiting chips that will let me test multiple bios til I can figure out whats up with the RAM issues (seeing only 1MB, not 4MB).