Over the last year I've lived in my current home, I've occasionally used my old Pioneer SX-212 stereo reciever to listen to old 8-tracks. I have four old speakers, two small EPI's and two larger Sony's, connected to the reciever, and when I turned it on today I found I only had sound coming out of the right speakers. I opened up the reciever and blew out the loose dust, and saw no obvious problems. Any clue what could be wrong?