I managed to get hands on a service manual (in German and in English, or the later more a crude mixture of German and English
). If it's any help for you, write me a mail and I'll scan it.
The adjustment procedure is:
Electrical Adjustments:
1. Apply supply voltage 8V to battery clip
2. Turn on device
3. Attach measurement device to supply + and contact area E
4. Adjust LCD voltage to 4,3 V using pot R105.
Reference voltage adjustment:
1. and 2. like before.
3. Main switch to V=
4. Apply 250 mV (source resistance < 100 Ohm) between input mass and test point A (input socket?)
5. Adjust to 2500 digits using R36
Capacity:
1. and 2. like before.
3. Main switch to F
4. Apply 250 nF between 250 mV between input mass and V socket (input socket).
5. Use R72 to adjust to 2500 digits.
That's all. The rest of the manual is just an explanation of the schematic, the signals expected at some test points - and the schematic itself, of course.