I feel like isolating the flipper by grounding out its transistor could prove helpful. If my calculations are correct, if your flipper wont fire after grounding it out, then its either an issue with the wiring of the coils or a cracked solder joint on your flipper board.

You could take a digital multimeter to the flipper board and check for continuity and resistance and just simply look up what the specs should be. If its a bad transistor you can just solder in a new one. Or replace the board your call.