Forgot to mention.
After some time a message appears:
off board parity error

https://theretroweb.com/motherboards/s/minta- … ies-co-pcb-201s
over 30 years old, big board, looks 2 layer? something could have cracked in transit like solder under simm sockets, plcc sockets arent the most reliable either

What type ram are you using ? Can you post a picture of them ?
The board accepts 256k and 1Mb Parity 30 pin. You need at minimum 2, start in bank 0. Make sure you set the dip switches proper.
They should be 9chip type (3 chip type may work but doubtful) and at least 80nS or faster..
added: never seen jumpers for "low " and "high" parity before. Maybe has to do with those...I cannot tell from the picture if they are disabled..

@rasz_pl
Thanks for the link.
Hard to say if cold joint or something else happened to it on the way here.
Will run it with the hotgun tomorrow. Maybe even bake it. Will see.

@Horun
What tried so far:
2x256Kb
4x256Kb
2x1Mb
4x1Mb

Tested the switches combos both ways:
- ON is "C" for closed
- ON is "O" for open

The 256Kb SIMM modules are 5 chips. Or were they 6 ? Cannot remember right now. Away from them.
Tried 1Mb modules with 3 and 9 chips.

No difference so far.

Looks like you've got buffers on your memory bus, they can be trouble. Look socketed so maybe swap them over see if the error changes.

Edit: Oh wait, someone maybe replaced an F with an HC there, maybe it isn't quick enough.

EditII: if error goes away when you put 60ns in it, I bet that's it, can't take the extra few ns of the latency through the HC with lower speed RAM.

Tried 60ns already.

Was looking in the pile with broken HW for spares for the socketed chips …

before replacing anything try deoxit all socketed chips

BitWrangler wrote on 2024-04-01, 03:42:

Edit: Oh wait, someone maybe replaced an F with an HC there, maybe it isn't quick enough.

exact same combination on theretroweb picture, looks like factory setup

Could try a slow oscillator and underclock the board, if something is flakey that can get it stable enough to run a post card

Wait, it's not being a dumbass because it's CMOS settings are invalid is it? There was one machine I came across way back would only count first 64k, would give checksum failed on the same line, then if I waited another minute or two, got POST screen, loaded defaults in setup and it was all good. Just saying some boards aren't real clear about what they are failing sometimes and some don't count full RAM until setup run, and some are jerks about both.

edit: come to think of it, was a fairly similar looking AMI BIOS 286, same size and color PCB, but had a bank for discrete RAM chips and 4 SIPP on, also learned me about the color cycle option on AMI BIOS because it came up in that eyeball melting pink and green as default.

Ok, so the order of ops:
1. Try what BitWrangler said. I admit, i didn't wait long enough. But in some configs i do get parity error.
2. Try replace the two socketed chips next to SIMM slots. If i find counterparts - easy, so why not do it.
3. Downclock further. Also easy - one crystal oscillator socket insertion.
4. Not sure what deoxit socket chips means. Have to look it up.

"The DeoxIT contact cleaner is a fast-acting deoxidizing solution"