I usually have great guiding on my AM5 - below 0.5"RMS is normal and I have seen it below 0.3" for a few brief periods. However, DEC can fail suddenly - it doesn't drift, it just drops off the chart, sometimes North, mostly South.
I am below weight capacity and reasonably well balanced and have good Polar Alignment. DEC belt is properly adjusted, at least tightening made no difference (possible made it worse?). Just how tight should it be? ZWO support just said "tight". No issues with cables either. Using NINA I can get guiding back on track with a simple Stop Guiding/Start Guiding command but sometimes it may take several attempts. Once guiding again, it can guide perfectly for long periods.
It seems to happen only when the scope is point to a high altitude and when pointing West. I can almost guarantee it will happen after a AF (I have an OAG and stop guiding for AF) but sometimes mid exposure too. There is no issue with the Meridian Flip. PHD2 does nor report a lost star and the issue can happen on the calmest night with good seeing.
Has anyone had a similar experience and if so, did you fix it? Or suggestions? I have to babysit the mount and its driving me crazy! Thanks.