I own a Crate CSM 8 Stereo Mixer, recently, on Channels 1,2 & 3 I don't get any sound from my right side speakers. Everything works fine on channels 4 through 8, when using the balance of left to right. We just happened to notice it when we couldn't hear "certain" singers on the right side of the church. Amp, and snake check out fine. We have tried blowing canned air into the sliders, but to no avail. What else could this possibly be, and it is expensive to repair?