I think the intent was just to verify the drifting and to note if it was in RA.
Periodic error is NOT drift. The two things are quite different. Drift is a continuous motion in one direction which eventually moves the object completely out of the field of view.
Periodic error is simply a back and forth movement of the object (or star) over a distance of about 5 - 7 arc seconds. The trail of the star movement often has a brighter point at the beginning and end of the trail, just like your 5 minute image shows. This is very characteristic of periodic error, and is not characteristic of drift, where the star trail has no brightening anywhere along the path. Judging by the number of pixels in your posted image taken with your camera, I would estimate that your periodic error is somewhere in the 5 to 7 arc sec range and seems to be quire regular. This means that a simple re-doing of the PE curve and downloading it into the CP controller will get you back to where you were before.
Now here is what I think happened when you suddenly had this "drift". I'm betting a bowl of ice cream that somehow you inadvertently erased the PE curve in the mount memory during one of your setups and you actually have no compensating curve at all. That would explain why turning the PEM on does not change anything. Because there is nothing there in memory. PEMPro can dig out what's in memory, another very useful tool of that amazing program. If that's the case, then you can be assured that nothing has happened to the mount's mechanical integrity, and I can sleep peacefully for at least one night.
To: ap-gto <ap-gto@...
Sent: Sat, May 11, 2019 11:53 am
Subject: Re: [ap-gto] Re: Mach 1 tracking problem
Thank you for the in-depth and clear explanation of things to be aware of and check. I did the 5 min at George's request. I think the intent was just to verify the drifting and to note if it was in RA. DEC, or both. In any event, I will press on and figure this out.
I will call the office next week for the grease kit.