If there's no sound at all from the channel, I suggest a simple test. Put a small piece of wire into the center connector hole of the input RCA plug. With the amplifier on and selector to phono, you should create a hum when you touch the connector. There is 60Hz noise coupled into your body from power lines around you and this makes a pretty strong signal for a phono input. You'll hear the hum if the amp is working. Test on the good channel to make sure you're doing everything right and if you hear the hum on the good channel but not when you move to the bad channel, then it's your receiver. If not, it's your turntable, cartridge or cables.