dill nailed it. Only thing to add is if you carefully slowly and slightly tap or turn the selector switch while the speakers are playing and it causes the sound to cut in or out that is confirming its the switch and not something else.
Right Speaker input not working!
I recently bought a Soundscraftsmen 3000A Solid State Stereo Receiver along with a Kenwood KD-3100 turntable. The issue I am having is with the speaker inputs. It has inputs for 4 speakers. The two on top are for left speakers and the two on the bottom are for the right speakers. The left speakers work perfectly fine. The bottom inputs for the right speakers are the issue. They will work for about 5 minutes and then it will sound like the speakers are blown out. Everything is wired correctly. When I wire both speakers to the left they work perfectly fine all day. It's the right speakers that are the issue. Check the fuses too and they're brand new. Would anybody know what might be wrong?