The Addams Family (Bally, 1992)

Symptom: Shorted magnet driver transistor
Location: Lyons, Colorado.

This is a case where a component failure revealed a design flaw that has been plaguing Addams Family pinball machines. There have been a lot of reported problems with the magnets under the center of the playfield that are energized in some modes like the seance mode.

(Note: the “too long; didn’t read” answer here is to remove D17 from the Power Driver board.)

On this particular machine, transistor Q1 on the magnet driver board which is mounted on the underside of the playfield, was shorted. This transistor powers the left magnet. I replaced transistor Q1 only to see smoke appearing a few minutes later. The transistor was very hot. The magnet checked out okay, with a resistance between 4 and 5 ohms. Upstream from Q1 is Q44 located on the Power Driver board. I tried replacing Q44, thinking that it wasn’t turning off all of the way. It didn’t help.

While checking on possible causes, I noticed that the solenoid power in the machine was only measuring about 47 volts. But the voltage to the magnets was about 70 volts (normal). This difference was abnormal since both power supplies have the same AC source. The oscilloscope revealed that capacitor C8 was bad on the Power Driver board. This capacitor filters the pulsating DC from the rectifier bridge (BR3). Although the schematics show the voltage as being 50 volts, it will measure 70 volts with no load (i.e. no solenoid powered on).

After replacing the capacitor, the Q1 transistor no longer got hot. I still needed to answer the question as to why it was getting hot in the first place, and why the other two transistors for the other magnets were not doing the same thing.

Simplified schematic of the magnet driver circuits. Click for larger.

The schematics from the manual don’t show it, but the magnets are powered by the Extra Flipper Power Supply board, which also powers the upper flippers on the playfield. All other solenoids are powered by the Power Driver board.

With the failure of capacitor C8, the solenoid power supply had a lower average voltage than the flipper power supply. Following the arrows in the above diagram, the power supply with the higher voltage flowed through the magnet, through R1, and through D17 to the power supply with the lower voltage. As the current went through R1, a voltage drop developed across R1, which turned on transistor Q1, causing more current to flow to ground through the transistor, which turned on the magnet (at least partially). The magnet and the transistor are only designed to be turned on in short pulses, not continuously like in this case which causes overheating.

After the capacitor was replaced, the voltage on both power supplies was the same. The current was no longer flowing from one to the other, the transistor turned off, and there was no power going through the magnet. UNTIL…

When any of the solenoids fire such as a pop bumper, slingshot, or ball kicker, the voltage on that power supply will drop, thus momentarily turning on transistor Q1 again. On a heavily used machine, where there are a lot of multiballs, I believe that transistor Q1 overheats and eventually fails.

The other magnet driver transistors are not affected because diodes D11 and D12 are not connected to anything. Their cathodes connect and dead-end at connector J126. So only D17 is causing a problem. These tieback diodes are only used when the driver transistors are directly driving a solenoid coil. In this case, the driver transistors are driving another set of driver transistors (ones that can handle the increased power of the magnets). So these diodes are superfluous. The actual tieback diodes for the magnets are on the magnet driver board (see D1, D2, and D3 in the schematic above).

The solution is to remove D17, which is simple enough to just cut one end of it with a wire cutters. Once the diode is cut, the Power Driver board can’t be used in a different titled machine without reinstating the diode. The Power Driver board is used in many Williams pinball machines from the era and is not customized for each game title.

Gold Wings (Gottlieb, 1986)

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.

Popeye Saves the World Pinball Machine (Bally, 1994)

Switch matrix failures associated with Bally and Williams WPC systems

Failures of the switch matrix system in a Bally/Williams WPC system will often show an error message when the pinball machine boots up. The error message will usually say “Ground Short” with a row or column number, or “Check Fuse F114 or F115”. This is a serious problem that will require board repair. While this post describes specific issues with Popeye Saves the World, over the years I’ve seen this problem on Terminator 2, The Shadow, as well as other WPC machines from 1989-1995. Sometimes the problem is related to battery corrosion damaging the CPU board. This post describes trying to track down problems unrelated to battery corrosion.

Generally the failure is caused by a switch signal shorting against a light socket or a solenoid coil. Based on anecdotal experience, if you get the Check Fuse message, a switch signal has shorted with a coil. This often blows out the 12 volt regulator on the Power Driver Board. So the first thing to check is the 12 volts DC. In the case of this Popeye machine, I checked the voltage on the F115 fuse clips and saw 14 volts. I replaced the 7812 regulator. I replaced the fuse only to have it immediately blow again. So something downstream was still shorted. I unplugged the connections J114, J116, J117, and J118 and powered up the machine again. This time the fuse didn’t blow. I added back the connectors, but unplugged the CPU board power connector J210, and still the fuse was good. This shows the 12 volts was shorted on the CPU board.

Usually when a switch matrix signal comes in contact with a light socket or coil, the U20 chip blows. This is a ULN2803. The 12 volt power is also connected to this chip at pin 10. I cut this pin and the 12 volt power was no longer shorted to ground (tested with ohm meter). I replaced the chip and reinstalled the board, but did not turn the power back on.

Next was to find the needle in the haystack, the short that was causing all of this circuitry damage to begin with. It requires careful inspection of everything above and below the playfield and in the cabinet. In this case, since the 12 volt regulator was bad, I was focusing on ways a coil voltage could enter the switch matrix.

I found that the Right Cheek switch (62) was loose and its terminals touching the metal trough of the Bluto ball lock. There are two coils mounted to the ball lock mechanism, one is a release coil the other is the kick-out coil. The kick-out coil was loose because the coil stop had loosened up. As a result, the side of the coil was rubbing on the metal bracket that holds it. A winding on the coil has shorted against the metal bracket.

This shows where the winding of the coil shorted through the wrapper and was touching the metal of the ball lock mechanism (circled in red).

In all of the other pinball machines listed at the beginning of this post, it’s been a case of a coil winding shorting against a metal bracket along with a switch signal shorting against the same bracket. I’ve only seen this with the fatter coils such as the 23-800 and 26-1200 coils because the coil windings are the same width of the plastic bobbin.

At this point, the coil can be replaced or insulated with electrical tape. And of course, the switch tightened up so that it was no longer touching the metal ball lock mechanism.

Indiana Jones: The Pinball Adventure (Williams, 1993)

Location: Littleton, CO
Symptom: Path of Adventure not working

One of the features of the pinball machine, Indiana Jones and the Pinball Adventure, is the Path of Adventure. From a servicing perspective, it could be renamed the Pain of Adventure. The Path of Adventure is also referred to as the mini-playfield in the diagnostics and error messages. It is located in the upper left of the main playfield.

Upon entering the mini-playfield test from the TEST menu (T.15), the software will run a quick left-right test of playfield. If the test is good, but you still have a problem with the playfield moving during game play, the problem is in the flipper circuit which is outside the scope of this article. If the test is good, the playfield will be level. Usually if the test is bad, the playfield will be tilted one way or the other. If the test shows the mini-playfield as bad, then read on.

View of opto status of working mini-playfield. Note the 5 dots that represent the light beams of the opto sensor. This is key to diagnosing problems with the mini-playfield.

Pressing the red + or – buttons should move the playfield left or right. If one of the left-right opto sensors has failed, the playfield will cease to move, making you suspect it’s a problem with the motor or the drive circuitry. The way the software is written, it will not move left or right if the sensor already says it’s there. When an opto sensor fails it is interpreted as the light beam being blocked which is the same as the mini playfield being in the left or right position. If the motor appears to be stuck in the left or right position, the problem is usually with an opto sensor and not the motor.

For example if the left sensor is bad, and the playfield is in the right position, it will not move in either direction because both sensors are interpreted as blocked and the software won’t move the motor. The display can’t show it being in both left and right positions at the same time. But it will show the light beam missing from the opposite sensor. You will not be able to manually move the motor in any of the test menus.

Mini-playfield test with one or both of the opto sensors not working. Note the missing light beam compared to the previous photo. When the lower opto or both optos are not working, the default is to show the playfield tipped to the right. In this case, the lower or “left” opto is bad.

In all of mini-playfields I’ve worked on, the lower or “left” sensor is the one that has failed. It may be just a coincidence.

If the following is done carefully, you can diagnose the issues with the motor without removing the mini-playfield. Open the backbox and locate Q30 and Q34 transistors on the large IO board. They will be transistors with metal tabs, just left of center. Connect one end of a jumper wire to ground (the easiest is the braided ground strap in the bottom corner of the backbox).

Enter the test menu for the mini-playfield. Quickly momentarily touch the other end of the jumper wire to either Q30’s or Q34’s metal tab. The mini-playfield motor will move. Grounding one transistor will move the motor one way, and the other transistor will move it the other way. If the motor runs correctly in both directions, the motor and the drive circuitry are likely good. Do not leave the jumper wire connected to either transistor so that it forces the playfield to extreme left or right positions and stalls the motor.

Using the jumper wire and alternately touching the transistor tabs, try to position the playfield so it is level, neither left or right. Verify that neither opto sensor is blocked by looking at the opto sensor board at the top of the playfield (if the mini-playfield is still installed, you have to look down in the crack above the top of the mini-playfield) and make sure the opto interrupting arm is between the sensors. Now look at the display of the mini-playfield test. If it still shows the playfield tilted left or right, then that opto sensor is bad.

Opto board with arm blocking the upper “right” opto sensor.

Often it’s a cracked solder joint or a broken lead on the opto sensor. It might be easier to replace the opto board. At the time of writing this, there are some aftermarket boards available. Search for the part number of the board, A-16657.

Removing the playfield generally isn’t too difficult as long as the head of the allen set screw which holds the playfield on to the motor shaft isn’t stripped. I usually replace it with a 8-32 phillips head screw. There are instructions for removing the mini-playfield in the manual on page 1-47.

With the machines I’ve worked on, the mini-playfield seems to move more to the right than the left. And, when in the center it seems to be tipped slightly to the right.

Wizard of Oz Pinball Machine, Jersey Jack (2014)

Location: Brighton, CO
Symptom: Crystal ball display not working

Crystal Ball on Wizard of Oz. This is not the original crystal ball supplied with the machine from the factory. This is an aftermarket version that features a larger glass ball, rather than a plastic ball.

The purpose of this post is to explain a little bit of what I’ve been able to learn about the Crystal ball display on the Wizard of Oz (WOZ). My hope is that will help someone else in troubleshooting problems with the display. Jersey Jack Pinball has been no help in this regard. My e-mail communication with their technician just stopped on their end. My customer had better luck, but ended up buying replacement parts he didn’t need.

The display is made by 4D Systems of Australia. I had a cursory look at their technical documentation (Serial Environment) to aid in my understanding how this display might be implemented in WOZ. There is a microSD card installed on the rear of the display. Images and video clips are stored on the microSD card and are selected by serial commands sent from the I/O board in the bottom of the pinball machine.

The first thing was to check voltages going to the display. The blue wire on the end of the connector is +5 volts (lets call this pin 1). Ground is the black wire on pin 4. The voltages on the other pins should be between 3 and 5 volts, except for brief moments during serial communication.

Display connector

Ultimately, the problem ended up being an intermittent cable issue. I had checked the continuity from board to board, which includes the connectors, and everything had checked good. But the display still didn’t work most of the time. Every time we thought the display was fixed, it would stop working. After re-pinning the connector, the problem seemed to be located further down the cable. Starting at the I/O board, I pulled some of the cable slack through the harness, up to the crystal ball. I cut off about 5 inches of cable and installed new connector pins. This fixed the problem.

During attract mode, the crystal ball display should display two video animations that coincide with the animations on the large backbox display, the green WOZ and the JJP logo being drawn (as shown in the photo at the top). In between these animations, the display should be blank. The flipper buttons can be used to skip through high scores and credits to get to the animations. I’ve checked this on two machines. When a game is started, the display will show the Skill Shot animation. If there was a previous animation running from attract mode, you will have to wait for it to finish before the Skill Shot animation starts.

The customer had purchased a new display and a new microSD card. However the old microSD card behaves differently than the new microSD card. After power-up, the old microSD card leaves the display blank until the animations start. The new microSD card allows the display to show the model number of the display and other information (upside down in the crystal ball) while the system boots up. Both microSD cards tended to miss the first or second animation cues after power up, but everything seemed to work fine after that.

You will not be able to read the microSD card in a computer. Windows will not recognize the file system on the card. Linux will see the card and show that 0% of the space is being used (i.e. blank). After reading the 4D Systems documentation, the microSD card is not using a specific file system. The serial commands reference SD card locations by sectors and not by filenames.

For more advanced troubleshooting with an oscilloscope, the RST signal, pin 5 on the display connector, will go low then high on machine power up. The TX and RX signals, pins 2 and 3, are unbuffered RS-232 style signals, with 5V as the idle voltage, with the signals going to 0 volts for the pulses. A command will be sent from the I/O board when an animation is to be started and the display will immediately acknowledge the command. As mentioned above, the flipper buttons can be used to skip over credits and high scores and start the animations.

The Addams Family Pinball Machine Playfield Replacement

A playfield replacement is where the original wooden playfield, with the artwork, is replaced by moving all of the electronics and mechanical parts to a new playfield.  One of the most common reasons for doing this is the paint may have worn off portions of the original playfield.

The customer’s machine was originally shipped to Germany where it was played heavily and not maintained well until being re-imported into the US.  While all of the paint was still on it, there was a mylar (clear film) that was bubbling up over the inserts (the colored plastic windows for the lights). The ball would not roll down the playfield without encountering one of these bumps, changing the direction of it.

New playfield standing beside old playfield.

I’ve done about a half-dozen playfield replacements. The basic and generic steps are as follows:

  1. Take many photos of the top side, both close and from further back, and from different angles.
  2. Remove the playfield plastics and ramps (if any) and retake photos.
  3. Continue to remove everything from the top side of the playfield, clean all of the parts and set aside. Determine which items you’d like to replace such as pop bumper caps, plastic ramps, etc.
  4. Flip the playfield over and take many photos from different angles.
  5. Continue to detach everything from the bottom side. The goal is to slide the entire mess of wires, coils, lights and mechs onto a temporary surface such as a large piece of cardboard (I use plexiglass). Label each light socket and playfield switch. Leave everything soldered with the exception of pop bumper lights and outhole kickout solenoid (and any other wires going to the top side of the playfield). Remove all staples from any wires. Slide everything off the playfield onto another surface.
  6. Do any hammering next.  If there are pop bumpers you will have to carefully hammer out the captive screws without bending them. Then you will hammer them into the new playfield. Remove the wooden edge pieces and back panel from the old playfield and install on the new playfield.
  7. On the topside, install pop bumper housings and light sockets. This is done now because the ends of the light sockets will usually need to be stapled on the bottom side.  You’ll have to use a dremel tool with a small sanding drum to remove the clear coat from the center holes.
  8. On the bottom side, slide the mess of wires and mechs onto the new playfield. Do any stapling first while you can still move things around to get access with the staple gun.
  9. Install the screws for the remaining items on the bottom side. Sometimes the switches need precise placement and it’s best to drill pilot holes for the screws. On slingshots and eject holes, the arms and the solenoids are mounted separately.  The alignment is important to keep things from binding. Use the original playfield as a guideline.
  10. After everything is installed on the bottom side,  flip the playfield over and install all of the remaining items on the top side.


Bottom side of the new playfield almost complete.

During the Addams Family playfield replacement, all incandescent bulbs were changed to LEDs.  Also, spotlights and strip lighting were added.  Orange rubber rings and blue flipper rubber were used.

Top side of the new playfield being assembled. Rock wall decals were added to the back panel and the shooter lane ramp. (Click on any photo to see larger version)

Playfield lighting hooked up to a 6V power supply to test the General Illumination (GI) lighting. Jumper leads were used to power spotlights to determine the best position for them.

Completed playfield with various mods added, re-installed into machine.

TV mod at the top shows clips from the original TV series.

Swamp kickout on right has some purple and green LED strips. Likewise a LED lights up the pop bumper area.

Before installing the playfield into the machine, mirror blades were added to the sides of the cabinet. When it was all done, it looked like a brand new pinball machine. Just beautiful!


Last Action Hero Pinball Machine (Data East, 1993)

Symptom: not playing the correct sounds, some sounds playing backwards.
Location: Parker, CO

The pinball machine was playing most of the sounds correctly, but the background music wasn’t correct and at times played backwards, and sometimes Arnold’s voice callouts weren’t correct either. The sound test from within the machine’s test menu worked correctly.

I checked the electrical signals between the sound board and the MPU board with the oscilloscope and they seemed fine. I began to suspect a problem with the sound ROMs, so I brought the board back to my office where I could verify them, and they were fine.

At this point I dove deeply into the history and operation of the BSMT2000 sound system, which was developed by Brian Schmidt in the 1980’s. Supposedly “BSMT” is an acronym for Brian Schmidt’s Mouse Trap.  In any case, he developed sounds for many pinball machines in the 80’s and 90’s and also designed the sound system hardware. The hardware design was used by Data East, then Sega and then Stern. It’s basically a sample playback machine where the speed (pitch), looping, length and panning of a sound can be adjusted. From some of the sources I’ve read, up to 12 sounds can be played at once. It’s much like a digital sampling keyboard, but without the keyboard. The early boards were stereo with a center channel for the cabinet speaker.  Later circuits have parts eliminated and only monophonic is supported.

Since most of the sound board was working, I decided to create a test ROM that would test the RAM and then exercise the interface to the DSP (Digital Signal Processing) chip. Everything checked out okay, but I still had a sound board that wasn’t working correctly.

As I was staring at the schematic trying to figure out what else to test, I noticed “W6” and “W7” jumpers, which are connected to A18 of the sound ROMs.  On the schematic it says “W6 IS JUMPERED”.  The EPROM sockets will accept 27C010, 27C020, and 27C040 (1 megabit, 2 megabit and 4 megabit EPROMs, respectively).  Address line A18 is the highest address line for a 27C040 EPROM and when “W6” is installed, it connects it to +5V, which makes the socket only usable for ‘010 and ‘020 EPROMS.  But Last Action Hero has a ‘040’ sound EPROM. So what’s happening is it’s playing correct sounds from the upper half of the EPROM, and when it needs to play sounds from the lower half of the EPROM, it sees a duplicate data from the upper half. The lower half of the EPROM is inaccessible.

W6 and W7 jumper locations below the EPROM sockets (or above the sockets if the board is installed in the game)

It appears the schematics were never updated for machines that used 27C040 EPROMs, nor any other documentation to explain when the jumper should be installed in W6 and when it should be installed in W7.

So the rule is this: Any pinball machine with the 520-5050-0x sound board that is using a 27C040 EPROM, the jumper should be installed in W7 and not installed in W6. Any other situation requires the jumper to be installed in W6 and not W7. Do not install the jumper in both locations at the same time. It’s one or the other.

Some other machines that use this board and have ‘040 EPROMs are: Rocky and Bullwinkle, Tales From the Crypt, and Jurassic Park. I suspect that someone acquired this board from an older machine like Hook or Star Wars and put it into this Last Action Hero, without having the knowledge of the W6 and W7 jumpers.

Another word of caution:  I don’t think the BSMT2000 chips are the same across all the different sound board designs made over the years. For example, later sound boards have more EPROM sockets and the BSMT2000 chip would need to know that in order to utilize them. I don’t have any information as to tell the difference between the BSMT2000 chips and the version of the internal code.

Markings on BSMT2000 chip

Flip Flop, Bally Pinball Machine (1976)

Symptom: Not resetting, only adds players with start button.
Location: Littleton, CO

I’m always very happy when I solve a problem with a pinball machine that its had since it left the factory. This pinball machine would not reset when the start button was pressed. Instead it would add players. I was able to trace the problem to the #8 Cam-stack of switches on the score motor (the 8E normally closed contact to the reset relay coil).  There I found two wires on two leaf switch terminals that had never been soldered.  The wires were folded over the terminal, ready for soldering, but someone on the Bally production line must have gotten distracted. The wires were making a good enough connection for the machine to pass testing and shipped out to the first customer.  It’s unknown how many owners this machine has had over the past 40+ years, but I bet it was having this intermittent problem throughout its life.

I’ve probably come across a half dozen machines that have left the factory with issues. So far the machines have been in above average physical shape because they got pulled out of public service earlier due to their intermittent issues and sold to private individuals.  A few years ago I worked on a Gottlieb Circus that left the factory with a bad crimp pin connection in one of the connectors. The machine was immaculate.

Intermittent issues are very difficult to find, especially if the machine starts working correctly the moment I start tracing the problem. In this case I was lucky and the machine stayed dead until I found the problem.

Transformers, The Pin (Stern, 2012)

Symptom: Would not power up
Location: Firestone, CO

This is a home model pinball machine.  There is currently very little (none?) technical information about this pinball machine. It uses the Stern Spike system, which is used in some other professional machines and one other home machine (Avengers). I was unable to find any schematics for this machine or the individual boards. (I’ve read that Stern will be releasing some documentation in the near future.)

The machine would not power up. There is a 48 VDC power supply mounted inside the cabinet (you have to remove the bottom of the pinball machine to gain access to it). The 48 volts was working.

On the Spike MPU/Sound board (which is in the backbox), there are 4 LEDs to indicate the status of +48V, +24V, +8V, and +5V.  In this case the 5V LED was not lit. I found that D12 was shorted. Once D12 was removed from the board, I checked that D12 was truly shorted and it was. I also checked the pads where D12 was located, and it was still shorted there as well. This meant that the A8498 regulator chip (U30) was also bad. Once both components were replaced, I bench tested the board and all of the power status LEDs came on.

(Note: if the 5V is working, the +24V and +8V LEDs will only come on once the microprocessor has booted.  If the 5V is not working, then they will light regardless of the microprocessor.)

Stern Spike MPU board, 520-5318-01, from Transformers

The following is a more detailed look at the power section for other repair people who have the expertise to repair surface mount boards.This only covers the power sections and not any other functions such as sound, the microprocessor, or the interface circuitry.

The 48 volts from the cabinet feeds the 24 volt, 8 volt, and the 5 volt regulator sections. Each of the regulator sections utilize an Allegro A8498 chip, which is a 3 amp switching step down regulator. The enable pin (pin 2) for the 24 volt and the 8 volt sections are connected elsewhere on the board.  If the enable pin is not 0 volts, the regulator will be disabled (turned off). The enable pin for the 5 volt section appears to be grounded so that it’s always enabled.

Each regulator section consists of the A8498 (Allegro A8498SLJTR-T), a 68uH inductor, a 60V, 5 amp Schottky diode (Comchip CDBC560-G), and some input and output filtering capacitors (470uF at various voltages).  Near each regulator is a test pad where the voltage can be checked.  The 5 volt test pad is near the reset button. Note that the A8498 has a thermal pad underneath the chip which is soldered to the board. Only a hot air rework station will remove this chip.

Each regulator section consists of the following components. Refer to the A8498 data sheet for details on how things are connected together.

5 volt section: U30, D12, L8, C132, C135, C133, C134, R106, R107, R108.

8 volt section: U10, D4, L6, C55, C56, C59, C60, R24, R23, R25

24 volt section: U6, D1, L5, C47, C48, C49, C50, R125, R16, R18

The output of the 5 volt regulator goes on to power three other regulators: 3.3V (U9), 1.8V (U31) and 1.0V (U32). These regulators are Rohm BD18KA5W, BD18KA5W and BD10KA5W respectively. There are no LED status indicators associated with these regulators, however there are test pads near each one to check voltages.

Transporter the Rescue, Pinball Machine (Bally, 1989)

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.