Update Sept. 25, 2021
Since the last gear meshing adjustment degraded the performance of my GEM28, especially for RA, I adjusted it again and recorded the whole process:
iOptron GEM28 manual (Appendix C, page 36): https://www.ioptron.com/v/Manuals/G28_GEM28_Manual.pdf
I’m still not sure what to read out from the MGEN curves…
On the MGEN graph it’s visible that the DEC axis stays on one side for a long time and then suddenly turns to the other side. According to the MGEN manual this means that the gear meshing is too tight.
The GEM28 manual has a chapter for “Gear Meshing Adjustment”, so I simply followed the instructions.
All you need is a 2mm hex key for the 3mm hole to release or lock the gear meshing adjustment plunger and a 3mm hex key for the 5mm hole to adjust the gear meshing plunger itself.
Check the full instructions listed in the iOptron GEM28 manual (Appendix C, page 36).
I only loosened a bit more than 1/16 of a turn, visible on the next 2 images.
On the next clear sky I’ll take again the same exposure series like in my first test to be able to compare the recorded MGEN data.
Hopefully the DEC axis is adjusted well now. If not, I’ll repeat the whole process.