Yamaha CS80

I tune my CS80's (about once or twice a year) by ear. I use a digital 
synth, tuned to A440Hz to tune one channel (8 voices). I just press 
the key mentioned in the Yamaha adjustment manual on that synth and 
use a sustain-pedal to sustain that note. Then, I adjust the CS80 
trimmers to get zero beating. For the second channel, I use the first 
channel for reference, keep the room warm and put a towel on top of 
the boards to keep the heat there. Tuning goes quickly and efficient 
that way

I noticed just one problem on one of my CS80 while tuning: I can't 
get the reference voltage (adjusting vr3 BA-board) to 4,0 V. It's at 
3,96V so it's out of spec. I need to turn the fine-tune-knob quit a 
bit to achieve 4V so I didn't. Now, 2 voices have reached the limit 
of there vr6 (16'). I could change (lower) the fixed resistance (80k) 
folowwing vr6 by 1K but first I would like to know why I can't get 
that reference voltage to spec. Any idea somebody ?
However, I can't remember me repeating steps 8 and 9 of the tuning 
procedure, so maybe something went wrong over there...

At this moment, that CS80 is in tune, but next time I'm afraid I'll 
have to lower that resistors to 79k if I don't find another cause.

By the way, page 41 of the service manual mentions wrong resistor-
values for the transposition gates. For instance, it says 160K fixed 
and 4k variable for vr6 but it should be 80k and 2k. The large fold-
out schematics are correct in that aspect.

Still, I find it amazing that 16 voiceboards stay in tune for such a 
long time, without autotuning. Great job, Yamaha !