Yamaha CS80

Hi guys, wonder if anyone has had this one before... thought I'd ask first in case anyone could point me to it.

I just started to have a go at my out-of-tune 'M' card.
CP6 reads 0.5volts - when all the others read around 1.4volts

The voice is out of tune, and low in pitch. When I play that voice and then measure CP6, the pitch rises due to my meter prong's contact.

(I was thinking one of the FET's or IC7..?)

Cheers,
TOM