NAD 7140 input selector does not work

SOURCE: Yamaha DSP-A2070 intermittently fail to output audio to speakers

Probably selector switch when you turn to CD mode. The ball bearings inside the switch make poor connection resulting in intermitant problems to either speaker. Yamaha knows the selector switch is defective but has stayed silent. I've had mine replaced for $144.00 Can and it works AOK now. Different switch of course. I've had my problems with that switch for a long time and it was after a few years that a knowledgeable technician knew of the problem. Poor support by Yamaha! I'll never buy a Yamaha product again nor will my relatives and friends. Do the calculations and assess whether the cost of the switch is worth the value of the receiver. I think it is worth it as the receiver when it works is excellent. It is at a stage now when other problems could creep in though including corrosion on the boards and solder joints so have the technicians do a entire quality check at the same time...

SOURCE: DENON Input selector jumps randomly

I have a PMA-535R. Same problem but slightly different dialknob. I fixed it by spraying a contactspray and WD-40 into the knob itself. This does mean you have to disassemble the front of the amp and take out print of the dialknob. The knob has a plastic dustcovere that you will have to lift. Good luck