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Hi
Please see the attached picture.
The driven gear is the smallest of the three on each axis.
The idler gear is the one in the centre of the smallest and largest gears.
Lift the small gear, rotate it by one tooth and re-mesh. You should be able to reach the grub screw on the motor without having to loosen anything else.
Repeat until you have a period which can be corrected by guiding. At least a minute...
HTH

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OK. Now I understand what you are suggesting.
What I do not understand is how rotating the gear can change anything.
Well, if the gears are not exactly round then maybe...
I'll give this a try and see what happens.

BTW, 6-7 sec is exactly the time from one tooth to the next one while the mount is tracking...

Periodic error depends upon gears. Changing the orientation of the gears changes the periodic error.
You are trying to get to a place where the error is correctable by guiding.

I just had another session. Before that I moved the small gear by one tooth.
Of course it didn't change anything.
I have short term oscillations - 6-7 sec - which corresponds to the small gear pitch.
Moving the small gear by one or several teeth wouldn't make any difference.
I also have long term oscillations - which correspond to 638 sec (around 10 min) of the gear train of HEQ5.

Anyway. I switched to 1 sec guiding rate and it did improve things a bit.
Especially after midnight when the sky got darker.
Guiding below 1" RMS total.
At 10pm it was not as good (between 0.8 and 1.8 ).

I'm sorry it didn't make a difference. You have to be patient I'm afraid. The meshing of the gears produces periodic error. If one tooth makes no difference, try two etc. Adjust the meshing. Clean/recrease/reassemble.Look for burrs/dirt.
Have a look here for inspiration. This is on an eq6, but the method is the same.
Good luck.
www.cloudynights.com/topic/730464-having...st-mount/?p=10524592

My guiding did improve after all!
Clean/grease/reassemble helped.
For my initial tests I was using an FRA400 refractor (which is pretty light) and was getting just below 1" RMS total with occasional runaways up to 1.8".
That was actually more than adequate for FRA400.

Last night I switched to a much heavier RC6 reflector and boom! Now it guides at 0.6-0.7" total RMS with occasional runaways up to only 1.0".
This is the best guiding performance I ever had with this mount in two years I owned it.
Pretty happy!