[sdiy] CS-60 - VCO IG00153 is not linear

[Florian Anwander]

Hello,

This is question to the specialists for yamaha synth restoring...

I have this CS60 on the bench, and could solve all problems but the 
tuning of one voice-VCO. If I adjust the voice according to the manual 
(highest transposition, trim VR1 at C6, then trim VR2 at C1), then the 
tuning of notes around the C3 is ~20cent lower, notes in between are 
proportional lower
C1=0cent
C2=-5cent
C3=-10cent
F3=-20cent
C4=-20cent
C5=-10cent
C6=0cent
(these are not measured values, but it is like that)

The Keyboard voltage coming from the S&H section increases exponential 
like it should and like it is on the other voices

I interchanged the trigger and keyboard voltage with an neighboured 
voice card, but the mistune stays on this voice card. I did not yet swap 
the VCO IC itself (I don't like soldering too much on a part which is 
difficult to replace).

Is there any other part, which could affect the linearity of the VCO?
Any idea what to do?

Florian