Normally, the trough coil is de-energized through the 1-point and/or 10 point relay in the head, (a normally closed switch on one of these relays will open, breaking the circuit to the trough coil). Your problem sounds as though the 3 free-standing switches right at the trough coil itself need to be adjusted. Without looking, I believe the switch closest to the coil is the lock-on switch. When this switch closes, (during start-up), the trough coil stays energized until 1 or 10 points are scored. On Sweet Hearts, stays energized until the ball passes through one of the 5 rollovers up top. This opens the N/C switch on the 10-point relay and breaks the circuit to the trough coil.
It's very easy to accidently bump the trough coil switch stack when accessing something through the coin door, throwing off the adjustment of these 3 switches. Sounds like this happened on your game and that first switch is never opening. The first switch is N/O, the other 2 behind it are N/C. Good luck!