Yamaha CS80

Hi everyone!My CS60 was absolutely fine in tune, was....But only portamento don't work at all....And I live with it, but now decide to adjusting portamento with VR4,VR5 on KAS board....And ....absolutely don't mind why I adjusting VR6-VR13 and VR1,VR2.There are off tune my CS at all.I'm stupid.How can I make correctly adjusting VR1,VR2,VR6-VR13?When I set TUNE in central position on control panel, I receive on TU point on KAS 4.530V, not 4.000V.And when I adjust VR6-VR13 on 125mV, I don't correctly adjust VR1 and VR2.But there are not be enough adjusting range on VR1 if I set TUNE=4.000v.But I don't change the TUNE set at all after I buy CS in 2003 ( I mean that the TUNE was in central position and it was 4.530v).And sounds was great and tune everytime....And another question - when I measure voltage on 38 pin in IC2 in KAS board I must get ground (earth)  in EK point(black wires)on KAS?Oleg from RUSSIA.