Hello ig88, I noticed you mentioning having a QTA-770, as I have the same unit. Have you made any of the Cd-4 adjustments or alignments from the CD-4 board inside on this unit? Carrier level adjustment? My CD-4 separation pots in back of unit seem to work, but may need some cleaning for intermittent scratchiness when adjusting.
Don't know about The adjustment updates if they have been done to unit Available in library here But CD-4 pots need a very thorough clean Had same problem Scratchy ,gave it a good amount of deoxit