Right Rear Speaker not working.

I have a Sony DTR-DE635 and I'm trying to run surround sound from my tv and dvd set up. I have 2 front 1 center and 2 rear speakers. When I do a test tone everything works great except for the rear right channel. I've tried switching the speakers and it doesn't appear to be a speaker or connection problem. Could one of my channels be broken? Is it worth fixing or could I try to fix it myself.
Please help, I'm so close to a great surround sound!
Lloyd