Hi

>>The full set-up procedure is in the A-110 Service Manual, which is
>>available at the Doepfer website (there's a link on the A-110 page).
> Hmm... thanks but not very helpful, I do not wish to carry
> out such a procedure, as I may make the matter worse with
> the VCO.

Then you heave to bring it to a shop, who gives service for Doepfer.

Nevertheless it sould be quite easy:
- switch off the A100 system
- remove the screws from the A110
- do NOT disconnect the power of the A110,
- cover the soldering side of the A110 with a piece of paper; you
may fix it simply with an adhesive tape (This prevents unwanted
shortages, though it is quite diffcult to destroy really
something)
- switch on the A100 and let it warm up a quarter of an hour.
- set the "Tune" poti to center position.
- take a small screw driver and tune the VCO with the trimmer "P6"
(it is placed direct aside the writing "DOEPFER A110" on the pcb).
- DO NOT TOUCH ANY OTHER TRIMMER!
- switch off the A100
- remove the shielding paper on the A110's back
- fix the A110 with the screws in the frame

Best regards, Florian