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Harman Kardon Seven Twenty

Hello all:

I bought a model Seven Twenty FM tuner amplifier by Harman Kardon from the mid 60's. She powers up and tunes in fine, but there is a lot of hum. I need the service manual or schematic to fix the problem. Please help with any information you may have.

thank you,


Re: Harman Kardon Seven Twenty

I would first check ground connections (especially those made with screws) and the filter capacitors in the power supply. Also check solder connections at the RCA jacks. You may not need a service manual.

Re: Harman Kardon Seven Twenty

Thank you very much for the help. With the age and corrosion, the connections are a good idea. I think the filter capacitors are 2 caps in one can. Further disassembly is needed. She sure is pretty.