The Pot assembly consists of a planetary gearbox for coarse working on a standard 270 degree 100k pot, and a two standard 270 degree 1k pots direct connected to the thin axle.
The gearbox is made of plastics and very fragile. There was some dirt between the axles.
Electrically the pot assembly is okay. The problem was incorrect mounting in the front plate leading to contact between the knobs.
Now the VFO tuning is much more precise and coarse and fine do not interfere any more.
So far success.
But still not precise enough.
The pot assembly is mechanically weak constructed, so it would be better to put a standard 10 turn 100k wirewound pot with a gearbox knob as wme_bill mentioned.
For the moment I quit working on the device and wait for the manual.
Thanks for the support, season greetings, Jörg