Thanks for the suggestions Mark. ?All my fittings on the ST80 to the camera are screw-on as well, but to piggyback I did get the Losmandy-style dovetail instead of Vixen specifically for that reason (to attach directly to the mount), so I will give that a try.
Regarding the encoders, that's a good point. ?During my most recent attempt at installing the McLennan gearboxes, then subsequently going back to put the original pinion back on after not-so-good results, I had to disassemble the motor including the encoder cover in order to support the back of the motor shaft to press fit the pinion. ?This exposed the encoder disk, and while I was very careful not to disturb the disk, I can't rule it out. ?I did this to both motors, so I'll start by swapping the motors and test, and if the problem is still there, then its probably not the encoder (though I suppose its possible I damaged both encoders!). ?
Keith
