Coil activation is fairly simple. The banded diode side of the coil get's 43v and a transistor sends a ground to the other side.
To troubleshoot, turn the power off and make sure the solid yellow wire is soldered to the diode band side of the coil.
Unplug J5 from the SD board. Power up, does the coil lock on? if yes you have a ground short in the activation wire. If not you have a board problem.
Also make sure the 1A SB fuse by the flippers is just that. It should blow to protect the transistor from a locked on coil.