Zenith 40A

[ChuckA]

Anyone in the group have any experience with a Zenith 40A radio/phono? I have been trying for a long while to find where a loud hum problem is coming from when it is in the phono mode. I looked up the schmatic in Riders and the phono input is completely different from that shown.

If I shut off the phono motor the major portion of the hum is gone, I have replaced all the shielded wire from the phono to the radio chassis, no difference. I have tried adding ground jumpers from the phono motor, the input transformer with no change. I have tried lifting one end of the shielded cables thinking maybe I have a ground loop, but again no change. If I disconnect the phono connection from the radio completely and look at the audio signal it is clean.

Any suggestions will be welcome.

Thanks

Chuck