***Major SNIP***

I sprayed cleaner in the volume control, hum still present. Something
else.. the hum is audible no matter what input is selected from the input
switch, FM, AM, Phono, tape/aux. But there is a Monitor switch and when
switched from Source to Monitor, the hum ceases.

John C.



John,

Have you tried feeding a source into the monitor input and see if the
unit sounds OK? I'm guessing it will. While I don't know the HK-230A,
I have seen receivers that the tape monitor switch feeds the volume
control directly (or nearly so) eliminating the the tone control amps.

I strongly suspect that you have a low level (regulated) power supply
failure that is causing the hum. Looking at the power supplies that
feed the preamp circuits with an oscilloscope is going to be the hot
ticket here.

Tim Schwartz
Bristol Electronics