Today it opened further than it is supposed to do, jammed itself on the roll and the motor kept running and seems to have done itself some internal damage. I managed to release it/unwind it and the door shot down to the fully closed position. Motor makes a noise, when pressing the open button, but the door hardly moves as if something on the drive has stripped.
So I'm looking for some information on the internals of the drive system. The spindle is around 4.5" diameter and includes the motor and obviously must have some sort of concentric gear drive, which I suspect is the issue.