I have recently acquired a Mac 512k with SONY OA-D34V-22 floppy drive. I have opened the drive up and found the head has moved to the very front and seems to want to keep moving and therefore making a clicking noise. What should stop the head from moving when it reaches it's limit? Could this possible be a faulty sensor or PCB? The limit switch at the back of the drive is engaged. I have cleaned the drive up but still the problem persists. Not sure how these drives work so any help would really be appreciated thanks