When a coil is not engaged, there is no current return path on the switched side so both coil lugs will always measure exactly the same voltage.

Your problem is up in the head, likely at the solenoid driver board with an open circuit on the 5V logic power to the solenoid driver circuit. Check test point TP3 on the solenoid driver board. If it doesn't measure 5 volts, you have a bad connection on the brown green loop wire between pin 13 and 25 of the J3 connector on the solenoid driver board.

If the Knocker and coin lockout coil on the coin door are working then the problem is elsewhere. Run solenoid test mode to confirm their operation.

SDB_LogicPowerA.jpg

Sanding the pins is a short term solution. Once the tin plating is removed the brass pins will end up tarnishing and the problem will return.

Replace that pin header and the one at J4 next time you do a parts order.