Re: Case sensor
May have been stiction. One batch of 1GB IBM Spitfire disks, had the wrong lubricant in the drive bearings, which would vaporize and condense on the platter. When the drive was stopped, and the head parked, it sometimes stuck to the condensed lubricant, and would prevent the disk spinning up.
A quick shock would free the head and allow the disk to spin up.
I believe some other drive manufacturers also had this problem as well.
Biting the hand that feeds IT
