[Coco] FD-502

[Robert Gault]

Bill wrote:
> They fail with a known good controller. I have another controller, and the
> one works well with it, but the other two drives fail.
> 

What is the failure mode? Can they read disks from another drive? Can 
they format disks? Does the drive spin and if so is the strobe speed 
correct? Does the head move along the rails? Check for fuses.

There are several failure modes that can be fixed by cleaning, 
lubrication, adjusting drive speed, and adjusting the track0 stop. Other 
failure modes would need a scope and special calibration disk to repair.