Hey all! Question: I bought a used Mackie 1604 12 channel mixer on ebay and the balanced/unbalanced line inputs (chan. 1-6) seem to be screwy. When I patch in an mp3 from my computer via 1/4" cable I only get one channel... meaning, it's usually the instruments, but the vocals drop out. If I pull the cable halfway out and fiddle with it, I'll get the whole song, but it's at a lower level than the other channels with the less powerful preamps. That can't be right. Does anybody have a fix for this? This is my first mixer, maybe I'm doing something wrong?