Auf Gearslutz habe ich gerade dies hier gefunden. Da geht es zwar um den Zweier, aber das sollte ja egal sein.
Hi everyone! It seems like solution is here www.doepfer.com > English > Manuals > Synthesizers > Dark_Energy_II_technical_information.pdf > page 4 > Notes concerning the adjustment of trimming potentiometer P17 (VCO Scale)
A least Doepfer itself gave me this instructions. It works, not perfectly by overall pitch matching became better!
The point is that:
1. Power on unit
2. wait for warming up for a 20 min
3. unscrew like showed in a picture
4. tune the p17 potentiometer playing octaves
5 close back pannel but don't srew it on
6 wait 10 min
7 check tuning
8 if it a bit off - do again it from 4