Games affected: all
As far as I'm aware, bingos always used fast-blo (AGC) fuses, and the most common ones would be 10A (amp), 8A, and 5A. I've also seen 2A and 1A on games with solid state.
The purpose of a fuse is to burn out if the current through the fuse element exceeds the rating on the fuse. It works by heat. When the current gets high enough, the element literally vaporizes at it's weakest point - normally the thinner/smaller section. The slow-blow (MDL) fuses have a big coil of wire in them that can absorb/dissipate some of the current/heat initially, so a brief current spike above the fuses rating will not cause that big hunk of wire to disappear.
Someone mentioned a rather interesting point about fuses. They are rated for a certain level of current at a maximum voltage. You will almost always find the fuses to be 250V max these days. When replacing fuses, what matters is the current rating. If the game wants a 10A fuse, make sure it's a 10A fuse. The voltage part can be higher than what it says on the game (e.g. it is perfectly ok to use a 5A, 250V fuse in the slot that says 5A, 17V).
Personally, I always replace any slow-blow fuses with fast-blow, especially games with solid state. Most bingos I have came with at least one slow-blow fuse in them, and I doubt it matters much.
Anyway, most people know what a fuse looks like, so what was the point of this page? Well, you can get some info from blown fuses - assuming you have the clear glass kind. The ones with ceramic or cardboard tubes are nasty, since you can't see the element.
You will run across three types of blown fuses:
So, what happens when you are faced with case #3 - you replace the fuse and it blows again? Well, first, get a healthy supply of fuses, as this is going to be trial and error. Next, try and figure out at exactly what time the fuse is popping. If you turn on the power and it goes immediately, you can consider yourself lucky. If it goes at some point during the game, seemingly randomly, be prepared for some work.
a little circuit breaker that plugs into the fuse clips exists, but is probably getting harder to find. Auto parts places used to carry them. Karl found some at Parts Plus and provided part numbers you can try goohoobing for 10 and 15 amp breakers.
The first thing to do is visually inspect the machine looking for broken wires, burned coils, wires with insulation pulled back so they can short against other solder lugs or metal frames on units.
If the 50V fuse blows when the game is initially powered on, the next thing to do is manually trip the tilt trip relay and try again. When this relay is tripped, the 50V is cut off from most of the game. If the fuse blows when the relay is tripped, you have narrowed the problem down a lot.
If the 50V fuse blows only when the tilt trip relay is reset, then look at the schematic and start sticking a business card in switches connected to wire 30 and wire 21-3, cutting off power to sections of the game to try and isolate the trouble.
If the problem occurs intermittently when the machine is cycling, solder drips in the mixers/spotting/stepup discs can be the cause, or circuits related to trip relays. You can manually step up all the feature/score discs to eliminate them, and you can jumper 50V directly to the step-up coils to test them. Try manually tripping the feature-related trip relays to eliminate that stuff. The trip relays coils can be hard to reach/see, so it's usually easier to try and jumper 50V to a switch someplace that is connected to the coil.
For the completely elusive problem, you may have to resort to overhauling the machine so you can visually inspect the wiring...or do what the operators did - stack the machine in a corner and start taking parts out of it as needed to repair other games.
Oh, there is the one other, completely desperate, never to be tried method. Take the game outside away from flammables (like your house), and put a solid piece of wire in the fuse holder. Turn the game on and wait for the smoke/fire/sparks. What you are hoping is that the transformer won't burn out before you can see where the problem is. I've never tried this, and wouldn't suggest anyone else does either. I have seen a couple machines that this was done on, though. In one, a stepper unit got destroyed, and in the other, part of the wiring bundled burned and had to be cut out and replaced - about 60 wires - but in both cases, the problem area was found (though the specific problem was impossible to discover unless you are one of those people that can prove arson by finding a half-burned match under 40 tons of rubble).