I'm assuming this is a solid state game as you talked about the diode. Assuming the yellow 43v wire is not broken off, a quick test is to use a test lead with one end grounded to the frame and quickly sort the other end to the tab of the transistor. If the coil fires then the coil and wiring are good. If the coil does not fire try grounding the stiped wire side of the coil. That will tell you if it's a coil problem.