Here is a link to the service manual for your receiver. The download option (scroll down the page to see) changes from processing to get manual when it is ready to be downloaded.
The image shows the relevant part of the circuit.
You will notice that there are 3 relays A, B and S which need to be operated for the sound to be passed through to the speakers. These are protection relays, controlled by the microprocessor (on leads A sp, B sp and S sp), which release if a problem is detected on the output of a channel so as to protect the speakers from further damage, (and maybe even to prevent a fire!).
Firstly you will need to determine which relay A or B (I assume and hopefully they are in a clear plastic case which makes it easier to see) is released. After that you will obviously need to determine why.