If the diverter is locked on and balls are circulating endlessly, first check the transistors on the 8-power-board.
Is the tie-back in place?
The two diverters on the subway, and the two coils on the drop-target are daisy-chained.
If the tie-back to the board is broken or absent, this coil "cluster" is known to spike back current to this board blowing out transistors.