Let me walk you through what I've run into and done since receiving this amplifier. At first I had 3volts dc on the left channel speaker terminals so I replaced all out put drivers with the recommended replacements in another topic (FJP5200/FJP1943 (230V, 15A, 100W, 30 MHz)) also replaced all zener diodes, electrolytic caps and bias resistors. I now have music out the left channel but viewing a 1khz tone on the scope it's very distorted. The right channel sounds very very clean. I even bypassed the pre amp by cutting the blue and yellow wires from the pre amp out to the amplifier board and ran wire straight from the back of the aux input jacks just to rule out the pre amp but it didn't change anything. Still going to recap the pre amp as soon as I find a solution to the power amp. I have a decent scope so if I could get some guidance on where to look I could report back with my findings. Some of the early transistors have higher voltages than what's listed in the schematic. And distortion starts around qe1 and qe3 on the emitter I believe. I'd have to double check just going off memory here.