If it can benefit someone else with the same problem, here are two recent successful repairs
1) Eject motor of a 400k floppy disk driveMy disk drive was not ejecting at all, and I realized that the shaft of the eject motor was broken. After many days of research, I could not find a proper replacement gear motor with the exact dimensions. The ones that had the right screw pattern were higher RPM (300), and had a 4mm shaft (the original has a 3mm shaft). I then opted for a cheap 12V gear motor from China on eBay
https://www.ebay.com/itm/282025601397. It has the proper 60 RPM (one second per turn), 3mm shaft, but did not have the same screw pattern. So I glued it to the motor housing, and it worked ok. In the photo below is the FDD with the new motor, with the old motor with the broken shaft next to it. Oh, and I learned the hard way for why there is a 330 Ohm resistor in parallel with the gear motor. I first did not have it, but without it, the motor has so much momentum that it keeps going after hitting the switch, hence never stopping. With the resistor, the back emf eddy current slows down the motor before the switch has time to open again. At least, that's how I understand it.
Lisa mouseI bought a non-working Lisa mouse on eBay for real cheap ($40). I thought it'd be an easy fix, probably just a cleaning of the roller ball and contacts. Alas, I realized that one of the optical photodiode detectors for the "up" vertical motion was toast. After buying one that did not work, I finally found a replacement that worked with the right dimension, sensitivity etc..
https://www.mouser.com/ProductDetail/Optek-TT-Electronics/OPL560?qs=NVJATC80C4%252BsUnSPWSXvwA%3D%3D. In the second pic, you see the two IR diodes (left of the wheel), and the two photodetectors (right of the wheel). It's a bit tricky to remove, and put back the black plastic piece that covers this optical assembly, but with a bit of patience, I got it to cooperate. I now have a second working Lisa mouse A9M0050 !!
