What is the problem with this DC's gdrom drive? (see video)

See how the laser unit bangs around and makes a plastic clicking noise? This is not my video, but I have a 3DO console that suffers from the exact same problem (except the laser is at the other end of the track away from the spindle) and I'm not clear on what the issue is exactly. Manually moving the laser to a different location on the track does not fix the issue - as the drive will move the laser to this spot on the track upon engaging the drive where it starts clicking again.

https://www.youtube.com/watch?v=V7x0m14LuU0

What exactly is going on with this type of problem - any suggestions on what needs to be fixed or adjusted?

 

Worm gear is driving the laser to the hub and can't detect that it got there so the plastic bit grinds on the worm gear.

 

Is the problem likely an issue with the gear not meshing correctly? Or with some kind of switch/sensor that should be able to detect it is there, but is not? (If the latter, what should I be looking for when gazing at the cdrom assembly?)

 

More likely a sensor issue. Wish I knew where at and what to use as a replacement part.

 

possable to have a faulty gd-rom pcb.