I repaired about two dozen units in the past three years and twenty years past their service life the most common failure mode seems to be a failing photodiode

I repaired about two dozen units in the past three years and twenty years past their service life the most common failure mode seems to be a failing photodiode array which corrects for the tracking of the optical head. This is unfortunately beyond fixing by a hobbyist, so the minidisc format revival is effectively limited by the supply of working optical heads. Btw my first thought (and the general consensus of the md community) was that the units fail due to dying laser diodes. I designed and built a md laser power meter (https://github.com/fijam/md-lpm https://github.com/fijam/md-lpm) that runs off a coin cell and fits in a md disc case and every failed unit I tested had a working laser diode.