Tag Archives: Fuses

The Simpson’s Pinball Party (Stern, 2003)

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Symptom: Smoke coming from under playfield, line fuse blowing.
Location: Littleton, Colorado.

Summary: if you replace your fluorescent tube in the backbox with a new LED bulb, be sure to install a fuse in the lighting circuit to protect the large and expensive ($300+ USD) power transformer in pinball machine.

I started by installing a new fuse in the line fuse holder, which is located on the metal box above the power switch. Upon powering up, a buzzing and sizzling could be heard in the power transformer.

I unplugged all of the output circuits from the transformer, which if I remember correctly is 3 of the 4 connectors on the power transformer. This isolated the power transformer from the rest of the pinball machine. I installed another line fuse, powered up, and it still blew. This indicated that the power transformer had an internal short.

The owner of the pinball machine mentioned that he had replaced the 24″ fluorescent tube in the backbox with an LED replacement. It looked black on one end. To verify this was the cause of the power transformer failure, I measured the resistance across the blue wires coming out of the transformer. It read a short of zero ohms. The normal value would be about 3-4 ohms.

Sega/Stern chose to run the florescent tube from the secondary side of the power transformer. This was presumably done so they could use the same lighting circuit regardless of where in the world the pinball machine was shipped. If they had wired it in the power line side, then they would have to use different ballasts and starters for each country’s different voltage.

Sega/Stern didn’t include a fuse in the original fluorescent circuit, as shown below in the lower right. There wasn’t a need for one because the bulb acts as a fuse. If the ballast shorts, the bulb blows. If the starter shorts, the bulb blows.

In the diagram above I’ve marked in red where you can install a fuse, in either the black or white wires coming from the bottom of the cabinet.

Some LED tubes require the ballast to be bypassed. This is a great place to put a fuse.

I ordered and replaced the power transformer. When powering up, I left the blue wires from the transformer disconnected until I could verify that all of the voltages were fine. There was another fuse blown in the display high voltage regulator board in the backbox. I replaced it and the display worked fine. I believe this fuse blew when the transformer initially shorted out.

I reconnected the blue wires from the power transformer and tried another fluorescent bulb. The bulb burned out immediately, indicating the ballast was bad. With the power off I measured the resistance of the ballast, and it was 0 ohms. Presumably the LED bulb also took out the ballast.

I generally prefer to keep pinball machines original to their design. But since all three components of the backbox light needed to be replaced (bulb, ballast and starter) I opted to go the LED route, but with a fuse installed this time. A 1/2 amp fuse should offer protection of the power transformer.

I mounted the fuse holder next to the old ballast in the upper right of the backbox (forgot to take a photo).

World Cup Soccer (Bally, 1994)

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Symptom: Machine blows fuse F116
Location: Denver, Colorado.

This World Cup Soccer pinball machine would repeatedly blow fuse F116 during gameplay. Normally in a WPC system fuse F116 is associated with the switch matrix and the opto boards.

Display showing error message at boot up.

After checking for shorts in the switch matrix and not seeing anything, I replaced the 100uF capacitors located on the two opto interface boards. These capacitors failing is a common problem. But that didn’t solve the problem.

I removed fuse F116 and attached my meter to the fuse holder to measure the current flow. With the machine in attract mode, I was measuring about 1.4 amps. Fuse F116 is a 3 amp slow blow fuse. I started a game and as soon as the soccer ball motor started, the circuit was drawing 5 amps. This would surely blow the 3 amp fuse. It wasn’t obvious, but the soccer motor was powered from this 12 volt circuit.

Soccer ball motor

The soccer ball motor had an internal short on one or more of it’s windings. I replaced the motor and measured 2.8 amps in the F116 circuit with the new motor.

Gold Wings (Gottlieb, 1986)

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Symptom: Blows fuse
Location: Parker, CO

Sometimes things are not what they seem. There are many fuses inside a typical pinball machine. Generally the more modern machines have more fuses. When a fuse blows, the assumption is there is an overload condition downstream that needs repair.

Gottlieb, Gold Wings playfield

Usually when a fuse blows, it burns in the middle of the glass tube. This fuse was odd because it kept blowing on the end. The current measured about 4.8 amps and the fuse was rated at 6 amps, so it shouldn’t have been blowing. It turned out that the fuse holder had some corrosion on the clips, which was causing the connection between the fuse and the fuse clips to heat up. It got so hot, it melted the solder inside the end cap of the fuse.

The fuse holder was replaced and the issue was resolved.

Transporter the Rescue, Pinball Machine (Bally, 1989)

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Symptom: Machine is not working at all
Location: Greenwood Village, Colorado

The first problem the machine had were the batteries had been forgotten about. So the battery holder was replaced and new batteries were installed. All too common a problem.

While replacing the batteries, I noticed some burned circuitry.

Burned circuit in one of the pop bumper driver circuits

The burned driver circuitry was related to the lower pop bumper. Whenever I see this kind of damage, I always check the fuses.  Sure enough someone installed a 7 amp fuse where it should only be a 2 amp fuse.

Some of the fuses in an Williams System 11 pinball machine.

Out of the 6 fuses shown above, 3 were incorrect values, all higher than what they should have been.

The fuses are meant to protect against this kind of damage. Often in the history of a pinball machine, someone will replace a fuse with a higher rated fuse to keep it from blowing again without every investigating why the fuse blew in the first place. I’m not really sure why people do this. So instead of just simply having a blown transistor, the circuit board got damage and the pre-driver transistor, 7402 chip, and the coil were all damaged and had to be replaced. The 7 amp fuse never blew to protect the circuits.  Instead the transistor caught fire and burned until it acted as its own fuse and the circuit eventually opened.

The actual cause was the switch contacts on the pop bumper being adjusted too close together. Causing the pop bumper to energize continuously.

This wasn’t my customer’s fault. The blame probably goes to the operator who first purchased the pinball machine and placed in a public location to make money. A fuse or two probably blew and to keep the machine making money, installed larger fuses. Then eventually the pinball machine ends up in a home environment with the wrong fuses installed.