I have a Gossen Profisix, and a Lunasix F light meter. The second hand Lunasix was bought on E bay as a replacement for the profisix which was consistently misreading by a couple of stops. However, the Lunasix appears to suffer from the same problem. Both have been out of use for an extended period.
I fould that one trimmer pot on the Profisix (bottom right viewed with the back plate removed) appeared to provide adjustment. This was the first pot I tried turning and as it provided adjustment, I didn't touch any of the others. I have yet to carefully compare the readings from the Profisix with another meter/cameras for different light levels, but on the face of it, it looks like the Profisix is now reading correctly.
The board is different in the Lunasix - there is one trimmer pot visible, but it appeared to have no effect on the needle position. Perhaps this is for Flash calibration. There's a row of pots at the bottom of both the Profisix and Lunasix boards. Interestingly, the Lunasix has holes in the casing to allow adjustment when assembled, which are taped over.
Does anyone have experience of fixing/recalibrating these meters, are there service manuals and circuit diagrams available? I feel compelled to master this thing rather than send it/them back to Gossen.
Thanks and best regards,