VC2002 function generator service manual or calibration

I just bought a simple Victor VC2002 generator. It works but the Voltage display seems to be fully out of range. On the front panel it says Vp-p but actually it measures something half of p-p , so a Vmax. But even this value is about 20% wrong. I found an older post with a link to the schematics here (downloadable from Scribd). Unfortunately, the quality is so bad, that I can not identify anything. Does anyone have a better schematics? Or can tell me, which potentiometer is responsible for calibration of the voltage display value?