@technight

Do these drives have head positioning sensors for the home?

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Yes - it's an optical sensor that is very precise because on any reset or disk insert it sets the baseline for track 0 alignment. If that sensor is dirty or not reading for some reason, the head servo may keep seeking Track 0. It is fixed with one screw. If that was loosened or has been moved, you can have a lot of trouble trying to restore head alignment. It might be worth checking that the 3-wire connector to that sensor has not been damaged, it is quite exposed to any knock while handling the disk unit.

Rick