I've got a Williams Pinbot that has loud hum that I can hear on the other side of the room. It's not the normal hum that changes in tone with the CPU lamps. This is a constant hum that doesn't change at all, even when adjusting the volume control. All the boards are securely attached to the backbox. I pulled the sound board and went thru all the caps with my ESR meter and replaced all the ones that were bad. No change. I did the same with the MPU board. All the 100uf caps had either high ESR or their uF's were way off. I replaced all those and no change.
This pin had a Kohout Enterprises System 7-11a power supply in it when I got it. Not sure if that power supply is causing the hum or not. Unfortunately I don't have an original System 11 power supply right now to swap it and see.
Anyone else have experience using the Kohout System 7-11a power supply and if so did you get any loud hum?