You might want to double check the jumpers on the audio basis board if this machine is new to you and don't know if it was working properly prior to you trying it. I have seen wrong jumpers for Stereo/Mono card on A80RC that came from a studio.
Also A80 sends record and repro signal up to the VU meterbridge and get it back after level adjustment from the pots if it is in Uncal mode. I would suggest you start tracing the signal from input to the relay output contact. The other common fault on Record Amp cards I had experienced is with the A101 module...
However, above problems due to parts failure such as the A101 or reed relay going bad usually happen to one of the two cards and rarely to both at the same time. Thus, think about the possible cause as shared common function for both CH1 and CH2 such as the signal routing up to the VU meterbridge, etc.
Ki