Recently I acquired a second PS/2 Model 50 (I already had a Model 50Z), which was listed on eBay for spares. The machine was indeed dead (well, beyond reasonable repairs, but that's another story), but it did came with a bunch of parts I was looking for to use on my main PS/2:
386 upgrade CPU
Spare ESDI drive (you always need spares of these)
It also had a FDD. The case was badly damaged so there wasn't much to recover from that, however, the front plate for the floppy drive was in good shape. As a result, I decided to add this drive to my main PS/2 to have a second floppy drive (which is always useful, especially when dealing with reference diskettes). However, the drive from the other PS/2 didn't seem to work. It got detected, but it didn't seem to be able to read or write floppies. Last weekend I decided to take it apart to give it a good clean and inspect for potential failures, and I noticed this switch:
Sony MP-F77W drive, IBM FRU 72X8523, IBM model MFD-77W
This switch has four positions, and I discovered the following outcomes:
Position 0: not working; machine hangs during IPL and doesn't even boot the reference diskette from the first drive (which is a known working drive) Position 1: drive gets detected, failure mode as described above Position 2: drive works as expected.
I successfully wrote a floppy using this drive and read it in the other drive and vice-versa.