ChrisP2
Member
Lots of information out there on Marantz hum, major headache on this one. Low level 60Hz Hum - volume independent, source independent.
I checked all of the normal problem areas, power switch, phono preamp, preamp, rear jacks, etc. Pulled power on the Preamp, Tuner and Phono boards, hum still present on outputs, so appeared to be an Amp Board issue.
In poking around, noticed that the hum was impacted by the lead from the Amp Board to the Headphone Jack. Jumping the shield from that line (J714) to the chassis eliminated the hum.
Ultimate fix was to replace the two diodes in the protection relay circuit Q746, Q754 as well as C740 (10uf 50V) and pulling and resoldering the ground pin shown in the pic below (pre flux cleaning!).
Spent way too much time chasing this, hoping this helps some avoid doing the same.
PS - Watch the main caps, you will need to discharge every time!
I checked all of the normal problem areas, power switch, phono preamp, preamp, rear jacks, etc. Pulled power on the Preamp, Tuner and Phono boards, hum still present on outputs, so appeared to be an Amp Board issue.
In poking around, noticed that the hum was impacted by the lead from the Amp Board to the Headphone Jack. Jumping the shield from that line (J714) to the chassis eliminated the hum.
Ultimate fix was to replace the two diodes in the protection relay circuit Q746, Q754 as well as C740 (10uf 50V) and pulling and resoldering the ground pin shown in the pic below (pre flux cleaning!).
Spent way too much time chasing this, hoping this helps some avoid doing the same.
PS - Watch the main caps, you will need to discharge every time!
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