That fuse protects the voltage that goes to every coil and relay in the game.
The fact that it is blowing means that there is a short circuit between the two wires the carry 50v through the machine. It could be that there is a burned up coil or it could be a short circuit between two wires or even solder tabs on the switches. Even a stray screw or piece of metal could fall into the wrong place. It’s tough to tell.
The easiest thing to look for is a burned up coil. Sometimes they make it obvious.
After that, I’d begin with trying to determine exactly how far through the startup process you’re getting, and then use the schematic to trace what coils and relays are active at that point.
You can make or buy a circuit breaker that clips into the fuse holder to avoid going through a bunch of fuses. Alternatively, you could make what is called a “dim bulb tester”. It is commonly used when testing old electrical equipment to prevent excessive current from damaging what you’re working on. I use on in my amp repair work and have used it to solve a couple of fuse blowing pinball machines. When your game gets to the point where the fuse is going to blow, the bulb will go bright and the relay will start chattering. Then you know that you are close to the problem and you haven’t fixed it yet (but it prevents the fuse from blowing).
Good luck,
Dave
