Receiver sound go on and off?

[Lansky2013]

Hey guys,
I have yamaha rx-z1 receiver and lately I have problem with the sound.
Every here and there the sound go off with no reason and I have to turn the receiver off and back to on again in order to get the sound back.
This problem happened with all the channels so it is not coming from the DVD, tv receiver or anything else. It's from the receiver for sure!
The power doesn't go off its just the sound.
Anyone can tell me what can it be? What to repair/replace?
Thank you for your help!