Schritt 3 übersetzen
When you take the logic board off the hard disk body, inspect the flip side for any signs of serious trouble, blown chips etc.
(Back in the day of hard disks of 1-2-6 GBs capacity if the motor control chips were blown, we would swap logic boards from same model functioning disks and all was good again! This technique stopped working as disks grew bigger - logic boards must have gotten married to each disk's personal geometry and no longer generic-swappable.)
If all chips look good, look carefully at the contact points denoted by the red circles in the photograph. In this case the metal PCB pads were looking dull because of mild superficial corrosion (but I took the picture after the repair - doh!)