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