Still has the same "jumping" behavior, but I notice now that the altitude tracking is smooth, never a jump, it's only the AZ tracking that is jumping around. So, next will be to remove the cover on the AZ motor and inspect / relubricate. Will probably get to that tonight, but likely not be able to view again until Thursday night. Will post results and findings here. I know when slewing there is a definite spot around 140-170 degrees on the AZ circle where the motor sounds like it is slowing down and straining, so I assume the mesh needs to be loosened on this motor as well.
Couple of technical points--you likely have found a bad spot in AZ, even on expensive machining there is some eccentricity on a "perfect circle" -- it just gets less as the price goes up (usually).
One thing to watch out for is that in most positions the AZ takes the position of RA on a GEM and altitude does the work of Dec. Put more simply, your AZ may be turning three, four, five times or more for every one rotation of the Alt motor.
So--your perceived smoothness of the Alt motor may, in whole or in part, be a function of its being used less than the Az motor. Also in your tests, beware the dob hole. As you approach the dob hole the az motor has to work very hard to get nowhere fast (same as N pole in RA on a GEM). So the motor may protest and make weird sounds. If you want to test in AZ you sould probably tilt 45 to 60 degrees away from straight up, then as your adjustments are refined move to within about ten degrees of the dob hole as a final test. Of course you could swap the AZ and ALT motors and see if that makes a difference, one may not perform as well as the other. If the swapped motor in AZ makes the same sounds it's a good bet the problem lies in the gear and/or worm adjustments.
Your electronics may have a programmed stop to keep you from getting too close to the dob hole. Not sure why--a lot of dob mounts do, but have never seen it on a GEM for true N. Maybe I haven't been paying attention.
Edited by gnowellsct, 07 August 2014 - 03:42 AM.