Picked this up Thursday at goodwill. Tested it in store and noted the left channel out.
It's a Harman Kardon hk680i.
Got it home, opened it up and did a thorough look through. Did not see anything unusual until I looked at the bottom.
Some research brought me to a thread on Audiokarma regarding the hk690i and that they have problems with dirty switches and pots. Deoxit did not help, but when I took some of the stereo apart I found a broken wire. Re-soldered that and viola it works. HOWEVER in taking it apart I broke the memory presets led circuit board that a previous owner had already broke and "fixed".
Re-soldered that and put it back together but now it has a new problem. It randomly looses lock on station goes to static and the tuner display does random stuff. I will maybe try and figure out whats wrong with it later. Definitely can't sell it as working. It sounds good contrary to some reviews on Audiokarma of it "sounding thin".
I later removed the memory presets LED board and the stereo works just fine but there is no LED indication as to which preset is selected. big deal.
This stereo has some interesting features.
An adjustable FM muting pot on the back, and a stereo separation adjustment labeled "Blend" that goes from Mono to Stereo. Kind weird to see on a stereo from the early eighties. I would expect it on something from the MPX days of the 60's.