What concerns me is that the tracking error is not uniform PE…the star trails often have little jumps in it (see the attached image from a 100% crop). It almost appears as if it tracks for several seconds, then slips to a new position, then tracks for a little while longer before slipping again. What's worse is that the drift usually continues in a single direction, effectively tracking at less than 1x sidereal.
I have ensured that everything is properly balanced (slightly east heavy...I've also tried balanced and west heavy for the heck of it). I've torn down the mount, relubed, and adjusted the gears, etc., but nothing is working.
I am wondering if possibly there is a problem with the tracking motor that would cause it to skip like this, either with the electronics or possibly the internal motor gearbox. Have you any of you had similar problems before?
Part of what confuses me is that the tracking performance varies depending on where the scope is pointed. If I shoot at declination ~0 deg (M42), maybe 5% of the images are well tracked at 30 sec, but at ~60 deg (M81) I can get around 50% good images at 45 sec. Obviously, the linear movement of the stars is less closer to the pole, but I'm also wondering if there's something mechanical with the mount going on. This isn't just periodic error because each frame drifts farther in the same direction and never reverses direction. Longer exposures just create longer streaks.
I've struggled with this for far too long and I'm about ready to kick it to the curb and buy an Atlas/EQ-6 or CGEM. I like the SVP, and it's quite stable with the AT6RC, but it can't track beans so it has to go unless I can fix it. Do I have unrealistic expectations for this mount to give me 30-45 sec exposures with the AT6RC?
I should also mention that when I've used my 300/2.8 camera lens on the mount, I can only manage around 45s, maybe 60s exposures before seeing similar issues, so it seems to be somewhat independent of weight and focal length.