Mono only mode problem (by 4 users)

Toni5 gave the correct reasons for the problem you are facing.
But, instead of usinga file to clkean the relay's contacts, i normally use a fine grain emery sheet or Sand paper. Cut up a small patch maybe an inch square, and use these.

Oh, well in my case Tony5 is wrong, relays are blue and cover not coming up, as suggested JDSpin I took out the circuit board which is actually not that easy as he says (be patiend!!!) and just re-solder all of relays joints. If they are look just fine, You might want to take a magnifying lens to take a closer look on the joints.
Good Luck

Thanks JDSpin

Mike I have the same receiver and until recently had the exact same problem. It would click on start up and as it warmed up it got progressively worse, sound from the speakers was sometimes terrible and very muffled. However, if you tapped the top it would click again and them work again for a while. Anyway, I finally got around to taking the thing apart and found the problem was caused by dry solder joints to the relays attached to the main circuit board.

To fix it, take the cover off and you will see 4 blue relays in a row OSA-SS-212DM3. You will then have to take out the circuit board which is actually easier than it looks. Once you have it out just re-solder the dry joints. Alternatively take it to a TV repair shop and they should be able to do it for you relatively inexpensively. I hope this helps.

I had a similar problem, but all speakers would go off (not just one channel). I would hear a click and functionality would be temporarily restored when I over-twisted the A/B Switch, tapped the shelf and/or pressed on different parts of the case.

After several experiments, I found the solder joints were broken for the two sets of header pins for the board-to-board connectors on the Display PCB. These connectors link to the Muting and Power PCBs located on the left and right sides respectively. Because the through holes are not plated and there is mechanical interaction (board-to-board flex connection and in the case of the interface with the Power PCB--constant button twisting and pressing), these solder connections are especially prone to failure.

To confirm this problem, you will need to remove the front panel assembly (after you have removed the cover, remove eight screws around front plastic, unplug two flex cables and remove one end of ground strap). The back of the 5 pin header connecting the Display PCB to the Power PCB can be found on the upper right side of the Display board (marked with a "5" in a square); you may be able to see fractures in the solder connections or feel the pins wiggle; otherwise, you can easily confirm this problem with a continuity meter; make sure that you are testing the continuity/connection between the pin and the board itself while moving the pins/connection. The pins for the Muting PCB connector are on the far left side of the Display board (by "DISPLAY" marking).

Resoldering the header pens should restore happiness for a few more years of successful performance.