Any fuses in the amp???
try reversing it. If the outer shield is to the higher impedance side, it will be more prone to humming.
Does it stop humming with the bottom plate on? If so, put the bottom on
Dead channel sounds like a connection is loose somewhere, or maybe a terminal got bent over to ground.
Does it stop humming with the bottom plate on? If so, put the bottom on
Dead channel sounds like a connection is loose somewhere, or maybe a terminal got bent over to ground.