Sony HMK 77 Music Centre?

Distortion on one channel of the record player. Not the cartridge - tried another one - fault still there . It's somewhere in the two stage cartridge pre-amp as injecting a signal in after the pre-amp comes up clean & green. Checked likely components but can find none faulty. Electrolytic caps, the resistors and the two transistors are all OK. The low value caps (Pfs) can't check in circuit - not easy to get to the print side of the board - tuning gang sits on it - dial drive cord would have to come adrift - don't fancy coping with that ! Anyone out there had this problem ? I know it's old, but I like to play my vynals now and again.