Just purchased a QSC Touchmix 1600 mixer. Hooked up the main speakers (JBL powered). Only the left speaker has sound. No sound from RIGHT. Is there some setting I have to change in the mixer? OR, is this unit defective? I inserted the Right speaker cable into the Left channel and that works. In short there is no signal coming out of the right channel. I noticed an "L" with "AF" under the F on the main Fader. Not sure what that means. Any suggestions?