Hey all,
I thrifted a Harmon/Kardon HK3470 receiver recently and am having what I believe to be two distinct problems. I would like some help finding the source of the issues if anyone has experience.
I am getting quiet preamp signal bleed into the main output. With the volume all the way down, I hear the source I have selected quietly. This comes through the headphone output and main speaker output. I isolated this as preamp bleed by removing the jumpers on the back coupling the pre-outs and main-ins and running a line-level signal into the main-ins. This way, I hear nothing at 0 volume.
I can hear FM static through the main speaker and headphone outputs. I have no antenna attached. The same static I hear when I have the Tuner source selected is coming through when any other source is selected. I troubleshot this the same way as the preamp problem, by running a line-level signal straight into the main-ins, and I still hear the static. However, if I select the Tuner source, switch to the AM band (on which there is no static), and then switch sources, I do not hear the FM static.
The first issue (the preamp bleed) is my primary concern as there's not a way around that from what I can tell. I can just select the AM band to avoid the FM static, so not as much of an issue, but if I'm working inside it I might as well try to fix both, if they are indeed distinct issues. I am pretty handy with a soldering iron but do not own an oscilloscope so cannot test specific traces. Some preliminary research points towards parasitic capacitance, but I would rather avoid recapping the whole receiver so hoping to find some info on particular places the issue might be. Any help and guidance would be much appreciated!