My deck has been having weak output on one side for some time. Cleaning the tape head connector, resoldering and adjusting the gain pots do not fix the issue permanently. Until very recent it become more serious with almost no output level observed. Inspiration sparks when I tried on/off the power switch several times and hearing the relay latches. Bingo!. finally the rootcause has been found. Measured to find out there were few hundred ohms across the contacts due to oxidization, successfully restored with electronic contact cleaner. Before and after..
