Fuse 21 (3 amp slo blow) protects J10 pin #4 and #5. This is a 50 volt output . Wire color is yellow/violet. Follow these wire out to the play field to ensure that they are not pinched or the wire insulation has not rubbed through to ground. C

J10 pins 4&5 feed coil # 1,2,3,5,6,7,8,9,10,11,12,13 and 14. If the fuse blows as soon as you boot the game up and no coils are locking on, then you have a short to ground on one of the 50 volt feed circuits to one of these coils.

You have moving parts under the playfield that can rub wires if they are too close, and over time cause the insulation to wear off and contact the wire causing the short.