Receiver has a hum - Harmon Kardon 230A

Mark, The hum is there for phono, AM, and FM - so all source inputs. John

Mark,

As I recall from a question that John replied to earlier, his hum problem was on all sources EXCEPT the tape monitor switch. I suspect a pre-amp power supply issue, or a ground fault of some sort. It would be nice to have a print of the thing, but I don't.

Regards, Tim Schwartz Bristol Electronics

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Didn't you report earlier that you tried connecting a separate audio source into the tape monitor inputs and the hum went away? Did you mean completely, i.e. no hum problem at all in this case? That really sounds like a (mechanical) grounding problem to me. Especially since the volume and tone controls worked for this test, which would indicate that it isn't a problem with preamp/tone power supply ripple. Good luck.

That is correct. Hum is present on all sources EXCEPT the tape monitor switch. I can pug in an external tuner on the tape monitor input and there is no hum when switched to MONITOR.

John

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(Assuming you haven't fixed this yet...)

Does this have AUX input jacks? If so, and you connect your external audio source to those, do you get the hum? If so, with the unit unplugged, what is the resistance between the ground terminal of the TAPE IN (aka monitor) jacks and those of the AUX jacks?

Alternatively, if you hold a jumper wire between the ground of the monitor jacks and the AUX jacks (assuming there is no large potential between them), does the hum go away?

Apologies if all this sounds too simplistic.