I took everything off the mother board-RS boards, all the connectors, and removed the mother board from the tender frame. I looked at it and don't see any burnt or loose connections.
I checked the two wires that mount under the board to the tender frame-they're tight and no frayed wires touching anything.
I reinstalled the mother board. One by one, connected the wires to the board, each time turning on power afterward and listening for the hum. No hum from the mother board.
UNTIL, I got to pin J1, the hum is back! I checked it 3 times and each time it returned to humming. Here's a picture of the culprit!
So, I guess I need to take the bottom of the tender apart and look for a fault.
I still have no RS sound. Only the hum.
If I have time later, I'm going to use my known good speaker and see what happens. I wonder if I have more than one thing wrong with the sound?