Hi. I recommend that you review the stage of input, power and output of that channel since one of those or several may be damaged or a simple disconnection, but the most common problem according to my experience with this equipment is in the power stage where the transistors or integrated are located since it usually happens that some of them no longer work or all if it has more than one and causes the amplifier to fail. Do not forget to check cables, welds and connectors of input and output as it also happens that something has been disconnected and causes the equipment to fail, in this area the most common error or failure would be in the connectors since it may have been disconnected the ground (GND) at the entrance or exit or some with connectors and cables You can help yourself with a multimeter to measure continuity between the tracks and welds. I hope and this little information helps you. Best regards from Mexico.