@ArtsModelTrains, I think you have the right idea - disconnect everything and then run a pair of wires from B-U to the track lockon, no breaker, no TVS, just a pair of wires, and see what happens. If it still doesn't run, try the A-U terminals, they just provide a different range of voltage to the track. If B-U didn't work but A-U did work, your transformer may be the culprit.
George