As my two Disk ][ drives were making unhappy noises, I searched the web for some instructions but the german website I often see linked on these forums is not available anymore.
I went ahead and serviced one unit myself, I think I was very succesfull as the unit is now quiet and happy with most of the disks it would not read before. Speed is also ok. However, it would be nice to know if there are further adjustments to be performed besides speed - I do have an oscilloscope and I can do proper soldering! :) I see there are some trimmers on the main board - which I haven't touched of course.
Does anybody know is there is any more information on how to service those drives?