Hi there. I'm wondering if anyone here has experience repairing Mackie boards. My CFX20MKII has a 60hz hum in all output channels. I haven't been inside the unit yet, but am qualified to repair the power supply. I have done the basic tests for ground loops or noisy inputs. with all inputs off, the LF hum is in main, aux , sub, etc. I am assuming the PS capacitors need replacing, or there is a broken ground. Anyone have a schematic? Thanks.