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Ibm ps/2 model 50 memory problems... maybe?

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First post, by Kekkula

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So I got this good condition Ibm model 50 8550-021.
First I stripped it down and thought floppy disk drive caps have to be changed, but after opening the drive I noticed caps are just fine. At first the heads wouldn't move freely, but after many runs with lubrication I got them moving.
This is my first "working" mca machine so next I struggled with making right reference disk and getting all the right .adf files on the diskette.
Hardrive couldn't boot and files were mostly corrupted, so I tried to low-level format it but format on reference disk said disk is too damaged, so I tried with sstor. It seemed to mark bad sectors and formated the drive.
Next I tried to install dos on drive but started to experience lock downs, screen would just turn black and disk drive would spin endlessly. Then machine started to throw errors on boot, it would read just 256kb mem on startup memtest and hang.
So I started to diagnose the problem, I removed all cards including hard drive controller. Only floppy drive connected I booted memtest86 v.4.0 , at first it would boot and run some tests and fail, but after few boots it would fail to start even memtest86.
System has processor upgrade pcb on place of the original cpu, it has 386 sx25 installed, I could swap to 286, but I'm not too keen to touch the socket unnecessarily.
So replacing memory seems to be most reasonable next thing to do, after I first disassemble machine again and re-seat memory chips. But replacement ram modules for this machine are unobtainable.
Have anyone replaced their memory on this board, are there modern solutions?
All I could find is some monotech git page but I couldn't figure out what board should I order, and there were no assembly instructions.
https://github.com/monotech/1MiB_30-pin-PS2-SIMMs

Reply 1 of 4, by rasz_pl

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>it has 386 sx25 installed, I could swap to 286, but I'm not too keen to touch the socket unnecessarily.

I would suspect that thing ggetting loose before the ram

https://github.com/raszpl/sigrok-disk FM/MFM/RLL decoder
https://github.com/raszpl/FIC-486-GAC-2-Cache-Module (AT&T Globalyst)
https://github.com/raszpl/386RC-16 ram board
https://github.com/raszpl/Zenith_ZBIOS Zenith Z-386 MFM-300 ZBIOS disassembly

Reply 2 of 4, by Kekkula

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I might have dodged the bullet.
After few days I started testing system again... really didn't want to disassemble the whole system again, those plastic things break before give up.
So i took every card including hardrive controller off again. Booted with memtest86 and it would fail to start. What got me thinking maybe I had memory expansion installed when I briefly managed to run the test, and program isn't compatible with just 1meg of ram.
Next I Booted from dos 6.22 install disk and exited to dos and tested some games that would run from disk, and everything worked like charm.
Then I plugged in original hardrive and formatted it (boy did that take a long time since it had lots of bad sectors). I managed to install dos 6.22 and copied few games and all seemed to work fine.
Next plugged in the memory expansion card and tested with games and all seems to work, that's where I'm now.
Now I need to find some small test programs for dos to test the system stability. Small because I'm stuck with floppy disks and original ~20meg hardrive.
Does anyone have any ideas of what programs would do? I think checkit has some test at least.

Reply 4 of 4, by Kekkula

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Thanks.
(I got checkit to run it's through tests.)
I've seen adrians videos about that program I didn't remember it had dos program too... and I have network card with empty socket, would be nice experiment trying to get option rom booting from it 🤔
Edit:
Also noticed that power supply gets really hot with case open, had to add fan running on top of it, airflow is designed to go through the power supply when case it closed, supply itself does not have fan.

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