A micro-switch which should be activated (pressed) by the tray at the end of its movement may got damaged. Meaning that drive thinks the tray cannot be fully closed an opens it back.

Hm, that sounds plausible. Where could that switch be? I see that when the tray closes, the mechanism to bring up the laser and such latches and clicks in place, you can see this in the video, too. It is also locked so that you can't undo that part without moving the tray back, so mechanically it seems okay, so that a switch either is pushed back a bit or simply physically broken could be an explanation.

I'd really like to save this drive, seems like a shame to trash it when it's generally in full working condition.

I think it's that blue lever I indicated on the picture or it may be located anywhere at the back/front of the drive, connecting to the main board with the wires, or on the main board itself.
You will need to fully disassemble the drive. Remove the main board and you'll see it, if not go by the wires - you'll not miss it.

With this generation of Toshiba, I'd be weary of the plastics inside. These XMs have very brittle plastic mechanisms, I've had a couple SCSI ones just break on their own.

Zerthimon wrote on 2023-07-17, 07:42:

I think it's that blue lever I indicated on the picture or it may be located anywhere at the back/front of the drive, connecting to the main board with the wires, or on the main board itself.
You will need to fully disassemble the drive. Remove the main board and you'll see it, if not go by the wires - you'll not miss it.

Good point, I'll try to disassemble the whole thing then. It will be a little while before I find the time for that though.
Before then, I'll play with the blue lever and see if I can get anything to work manually. The lever does get moved as it should by the tray though.

I finally had some time and could get it fixed (more or less). I'm not 100% sure what the issue really was, but it was definitely purely mechanical. What happened was that the part with the laser did not get pushed up all the way, the drive detected that (because that blue lever wasn't pushed), and spat the tray out again - working as intended, I suppose.
What I did was lubricate all the moving parts (with WD40, because I'm a pro obviously... yeah, I know...) and then played with all the gears. Turns out, the tiny white gear in the left of the picture above was broken (little rip on one side) and should be replaced. I have no idea where I could a replacement though, so I glued the rip shut with a tiny bit of superglue (which kind of worked, the gear is definitely not perfect), and played with everything until it worked again.

Chances are, this isn't a permanent fix, but at least for now it's working again. Maybe I'll run across a fitting new gear some time, that should be a proper fix. In any case, it was a fun and interesting experience. Really feels a bit like Lego Technic. 😁

The problem with WD40 is that if dissolves plastics. You should have used silicone grease. Other than that - good job.