After an initial period of no probelms the left speaker channel sound deteriorates and then eventually there is no sound at all. I have had this checked 3 times by the service centre - each time they return it working perfectly no being able to reproduce the problem even though they witnessed this in my home environment. I believe this may be static related and the amp is not earthed as I live in Central europe and this is the standard wiring - unlike the UK that has an earth wire as standard in the power lead. This may explain that when earthed in the test environment that the problem cannot be replicated. I have switched the left and right speakers to ensure it is not them or the cables. The left speaker and cable performed perfectly on the right channel output and the previously functioning right speaker failed to work when on the left output channel. I have a DVD and CD player attached and a sub woofer powered through the amp.
Works great after this solution with the cables.
If that is the remedy, injecting signals to trigger... then probably it is a defective analog IC switch.
The problems lies with the switch relays in the pre-outs for the both the main and center channels. The fix, so to speak is to obtain a simple composite cable and while the amp is on (muted) insert and extract the cable from the pre-out/inputs, do this a few time for each channel and then check levels for each speaker. This is a know defect with this unit and it's really unfortunate that Yamaha never owned up to it.
Usually answered in minutes!