Oh dear... My 286 just gave a bit up on me. First thing I noticed for the last couple of days was that the 80287 was behaving weirdly. I wanted to do a bit more experiments with Autosketch, but it would always freeze. I then wrote a test program in Turbo C, which would also hang. However, I could break the program, so I figured that the 80287 might be broken, or at the very least maybe had to be re-seated.

So I just removed the whole thing, since I do not really NEED it. Being a rather large DIP package, I gently applied some force, first with a DIP tweezer, but then with a flat screwdriver under the IC. Worked fine. Closed up the machine, and suddenly after starting Windows I get GPFs... Then the machine would hang at memory check, then during boot: Parity error. I guess I will have to check all the RAM ICs... Oh no!

Could the 80287 have anything to do with that? My assumption is that maybe one or more of the following things happened:

1) The removal of the 80287 caused some RAM ICs to be not properly seated anymore, due to the mainboard flexing a little. They are placed near the 80287...
2) The 80287 socket is either a bit dusty/corroded and led to the FPU based hangs
3) The 80287 socket and/or one or multiple RAM sockets have wonky solder joints, since the board is now almost 30 years old and I replaced the RAM some months back (upgrade to 2 MiB)
4) Something under the mainboard is shorting some pins. The ATX case has cable management, so some stuff is running under there.

Anyway, I think I will have to rip everything out, and start out with only the mainboard, PC-speaker, RAM and CPU. Then adding VGA and more... This will definitely take a whole evening, or more...

Do you guys have any more ideas or hints?