I have a problem with my Marantz amp in that the front left channel has dropped dramatically in volume. If I unplug the amp for a while, it usually works again but the problem soon comes back. I sent it back a while ago to Marantz and it came back with a note saying 'general overhaul carried out' or words to that effect. Of course when they got it, and when I got it back, it had been unplugged for a while so would seem ok. Fault soon came back.