X68000 5 1/4 floppy drive error "disk is not inserted"

[Flag79]

Hello! I have a Sharp X68000 Expert computer with 5 1/4" floppy drives. One of the floppy drives is malfunctioning and gives the error "disk is not inserted" when I try to access the drive. The other floppy drive works perfectly, so I swapped them and the faulty one still gives the same error on the other port. I've cleaned the head with isopropyl alcohol and also replaced the capacitors on the floppy drive, except for the bipolar one, which I left as is. When I insert a floppy disk, it stays in place and I can eject it without any problems, and there's no strange noise either. However, when I try to read the disk, the error appears and the head doesn't move at all. I've also tested the other floppy drive, and the head doesn't move when reading the disk either, so I don't see any difference between the two drives. Do you have any suggestions? Is there a sensor I should check? Is there a way to manually move the head or the motor to check if it's moving correctly? Thanks for your help!