Cadette (CMM4), AMI/Rowe Jukebox (1970)

Location: Denver, Colorado
Symptoms: Wouldn’t make correct selections, if any.  Right channel sound was fuzzy.

I wasn’t able to obtain a service manual for the CMM4.  The closest thing available was a CMM1 manual, which ended up being of no help.  There were quite a few electrical differences in the mechanism, like different cam switches (CMM1 has 8 cam switches, CMM4 has 5 cam switches).  Also, the CMM4 has a tube amp and the CMM1 has a solid state amp.

The “write” side of the selector plate was working well.  The “read” side scanner would usually jump right over the selector pin, unless it was actuated by a pin on the outer ring. The pin reset solenoid wasn’t actuating.  Long story short, it turned out to be a bad stop switch.  The switch was reading many thousands of ohms when it should have been zero.  I drilled a hole into the side of the microswitch to try chemically cleaning it.  It helped bring the resistance down to about 180 ohms, but that’s was not good enough.  I found a compatible switch in my pinball parts and replaced it.  The jukebox made the correct selections after that.

The amplifier had a tube that looked bad.  Looking at it more closely, it had a crack in the glass at the base.  It was a 12AX7.  We used the tube from the left channel and the right channel started working.  The owner had a spare 12AX7 from a guitar amp that we used to get the amp fully working.

I also looked at the owner’s AMI G-120. It had a few minor problems that I was able to fix with some cleaning, adjustment and lubrication.

Moulin Rouge, Williams Pinball Machine (1965)

Location: Aspen, Colorado.
Symptoms: A variety of things not working.

The Williams Moulin Rouge is an electro-mechanical (EM) pinball machine from the mid-1960’s.  The owner has owned this game for over 30 years.  However, the game hasn’t been used in over 8 years.

When I first opened the machine, I saw some disconnected wires dangling from the playfield.  These were associated with the left flipper.  I re-soldered these wires to their respective places.

In the backbox, there were a couple of steppers that were sticky and needed to be cleaned.  The ball count stepper and the match stepper.  Even if a pinball machine has been set for free-play, the match stepper is important to have working.  The match stepper is used continuously throughout a game and is triggered by various switches in the playfield.  In this case, it controls various playfield features that alternately illuminate.

The machine wouldn’t power up due to a broken in-line switch that had been placed on the line cord.  I replaced the line cord, which had been previously spliced and installed a better quality switch.  Originally these games didn’t have power switches.  To turn the game off, you kick the bottom of the machine, which trips a “kick-off” switch.  To turn the game on, you press the left flipper button.  Kicking the bottom of the machine is awkward, so I prefer an in-line cord switch.

Once the machine was powered up, it was in continuous reset mode.  This is not unexpected with an EM game that hasn’t been used for a while.  A game will get stuck in reset mode when something isn’t detected as being reset.  In this case, the score reels were not being reset.  They were sticky and not turning freely.  Also, there was a dirty contact that was preventing the “100” digit to not get the reset pulses.  Once the score reels were fixed up, the game would reset.

The next thing I noticed was that the outhole wouldn’t register a ball after the first ball. Therefore it wouldn’t give an end of ball score, wouldn’t advance the ball count stepper, and therefore wouldn’t eject the ball to the shooter lane.  After checking the schematic to see what else was in that circuit and manually tripping the outhole relay, I noticed the scoring motor wasn’t indexing to its home position after either a trigger of the outhole relay or the eject relay. It turned out to be a couple of dirty contacts on the score motor bank that were supposed to keep the score motor running until it was indexed.

Next up, there were many lamps not working.  This wasn’t because the bulbs were burned out, but because the sockets and the lamp bases had corrosion on them.

Next up, the right slingshot wasn’t working correctly.  As the slingshot arm would kick the ball, it would get hung up on the playfield plastic over it.  The plastic was warped. I placed washers under the plastic to raise it up high enough so it wouldn’t interfere with the slingshot.

I replaced all of the rubber pieces on the playfield.

The left flipper needed a new bushing and was missing its torsional return spring.  The right bushing was okay, but both will be replaced on a future visit.

All in all, this was pretty typical work for a pinball machine of this vintage and the years of non-use.  People always ask me for estimates on this kind of work.  It’s very difficult because you have to start fixing things to see what else doesn’t work.  But it’s almost always in the 3-6 hour range.

Wurlitzer “One More Time” 1015-CD jukebox

Location: Soda Fountain, Lyons, CO

Symptom: Arm that holds CD on spindle wouldn’t release properly causing CD to fling against the back of the cabinet.

I don’t normally work on CD jukeboxes, but I made an exception because Lyon’s Classic Pinball is located across the street and that would give me an excuse to go over and play some of Kevin’s 35 pinball machines from the 1960’s through present day.

Sometime after Wurlitzer stopped making jukeboxes in 1974, the remaining Wurlitzer company in Germany began making some nostalgic jukeboxes with modern CD players. In the past I’ve worked on the original 1015 from 1946 that plays 78 RPM records, so this was interesting.

I spent some time familiarizing myself with the mechanism.  I looked at the lever that actuates the lift rod. Someone in the past had placed some rubber pieces at the bottom of the lift rod.  Not having a service manual for this jukebox, I didn’t know how it was originally designed.  It didn’t make sense how it was assembled.  So I disassembled the bottom section of the lift rod and reassembled it.  The lift rod and spindle arm worked correctly after that.

Examining the cam that actuates the lever, it appeared mushroomed in various places, which would have reduced the height of the lift rod, which probably prompted someone to put additional rubber pieces under the lifting rod. That cam will need to be replaced someday.

This post would make a lot more sense with either photos or some drawings.  Maybe in the future I will update it.


Golden Eye, Sega/Stern Pinball Machine (1994)

Location: Centennial, CO
Symptoms: Auto-launch ball shooter would not launch ball.  Lower playfield lights not working.

I opened the coin door on the pinball machine and immediately saw a coil dangling from the playfield.  It was the shooter coil and it was resting on the metal junction box.  It probably grounded out against the box causing the 50V supply fuse to blow.

The coil bracket had broken from the stresses and vibration of years of use.

The lower playfield general illumination lights were not working. I suspected a connection problem on the IO Power/Driver board.  I couldn’t find any problems with the connector. The lights started working momentarily on their own.  I could hear a faint buzzing that seemed to be emanating from the fuse.  I tapped the fuse and the buzzing would change. I removed the fuse and tested it.  It wasn’t blown, but there was a connection problem inside of it (more on fuses here).  I replaced it and the lights began working reliably.

Once the lights and the shooter coil were fixed, I played a test game and discovered a playfield ramp switch that was dangling with nothing holding it. I wasn’t able to locate any screws lying in the cabinet.  So I reattached it with a new screw.

Wurlitzer 2600 Jukebox (1961-1962)

Location: Boulder, CO

Symptoms: Some selections not played, record arm jamming.

When I first arrived the mechanism motor wasn’t working.  This was due to the Service Switch being off.  This is used to turn off the motor when making adjustments to the mechanism.  The normal operating position for the switch is on.

Once we got the mechanism running, the record lift arms were occasionally jamming against the sides of the record carousel.  Both right and left record arms are designed to raise at the same time.  If the carousel is aligned properly, one will glide into the record slot, while the other will stop against the record divider on the opposite side of the carousel.  Some of the record dividers were bent which caused one of the arms to get caught and then free itself, launching the record across the room.  Once I straightened the dividers, we didn’t see that problem again.

The jukebox played most records without problems, but some selections didn’t seem to work.  I tested each letter and each number selection to make sure the solenoids and switches were working.  There was no correlation between the non-working selections (i.e. there was letter group or number group that was not working).  I had the owner make selections while I watched the selector mechanism.  The rocker arms that release the selector pins were working but the pins were stuck.  After some cleaning and light lubrication, the problems started going away.  The owner is going to finish the cleaning and lubing on his own and will call back if he has any problems.



Sharkey’s Shootout, Stern Pinball Machine (2000)

Location: Boulder, CO

Symptoms: Ball trough solenoid not working — ball not delivered to shooting lane.

For some reason, this past week I’ve gotten a lot of Stern/Sega pinball machine service calls, and all machines are roughly the same era.

I started a game and no ball was delivered to the shooting lane.  The Dot Matrix Display (DMD) indicated it was ball 1, so the computer thought the ball should have been there.  I checked the flippers and they weren’t working either.  At this point, I suspected a blown fuse.

The flippers, pop bumpers, vertical up-kickers, and ball trough solenoids all are “high current” solenoids and run on 50 volts DC.  I checked fuse F21 on the IO Power Driver board and it was blown.  F21 is a 3 amp slow-blow (time delay) fuse for the 50 volt power supply used on these high current solenoids.

Portion of control board showing F21 and power LEDs (click for full res).

A quick visual check of the various voltages can be made by looking at the bank of power LEDs.

I replaced the fuse and the solenoids began working again.  I did a coil test from the diagnostics menu to see if there were any problems that would have caused the fuse to blow.  I then tested all of the switches.  Not seeing any problems, I concluded it was simply what I call a “fatigued fuse”.

Fuse fatigue occurs if the current in the circuit exceeds the rated value of the fuse for a brief moment.  The F21 fuse is a MDL time delay type of fuse rated at 3 amps.  If 3 amps is passing through the fuse, it won’t blow.  If 4 amps is passing through it, it will blow within an hour. It can handle 6 amps (double) for up to 5 seconds before it blows.  So a fuse like this can handle spikes in current without blowing.  But if coil or a drive transistor shorts out, it will blow protecting the circuit.

During multi-ball, the flippers and bumpers can energize all at the same time causing current spikes much greater than 3 amps.  After years of this, the fuse filament gets weaker and eventually breaks, like a light bulb burning out.

Which fuse is blown? The center fuse. See text.

The fuse on the left sure looks suspect with it’s black residue.  This is a fuse that I took from a high powered coil circuit from a different machine.  It still works.  It still measures good on an ohm meter.  I doubled checked by putting exactly 3 amps through it with my bench power supply.  It’s what I would call “fatigued” and probably will blow in the near future.

The center fuse is blown, but it’s difficult to tell visually.  The fuse on the right is intermittent.  It works for 15 minutes then stops.  If you turn off the power, it will start working again.  It’s the most bizarre behavior I’ve ever seen in a fuse.  It had me thinking the loss of power was somewhere else.

When it comes to fuses in pinball machines, don’t trust your eyes or your meter.  But if the fuse looks like the one on the left, replace it anyway because it’s about to blow.


Star Pool, Williams Pinball Machine (1974)

Location: Broomfield, Colorado

Symptom: Not powering up, not working.

This pinball machine is located in a youth center in a church basement.  No one seemed to know much about it, other than it was probably donated. So it was unknown when it last worked.

Given the age of the machine, before powering it up, I checked the mechanical operation of all of the steppers and visually checked the contacts on the relays and score motor cams.  Several of the steppers were gummed up, but the rest were in good condition.  I rebuilt the steppers and fixed the left slingshot linkage which was binding.

We had to drill out the lock in the back box because no one had a key and we couldn’t find one in the machine.

Once all of the mechanical parts were working freely, I powered it up.  The machine would get stuck in continuous reset mode.  The reset cycle description in the manual was nearly incomprehensible.  So I was on my own.

I checked all of the obvious things, like the score reels resetting to zero, the ball count stepper unit, player count stepper unit, etc.  Everything was being reset and all reset switches were working.  The only weird thing was the credit stepper was stepping up to the maximum allowed credits during reset, when it should be subtracting 1 credit.

It occurred to me to check the coin switches, which I hadn’t checked earlier.  They were a mess.  I think someone thought they could get freeplay mode by bending all of the contacts together on both coin inputs.  Once I got the switch wires and contacts untangled, the machine would reset properly.

I bent the switch contacts on the credit unit to give free plays.

After that, there was still some minor tuning needed and got 98% of it working well.  I discovered a broken switch contact on the Spinner Advance Stepper (EOS). It was broken right at the insulator which prevented me from soldering another contact on.  I am currently researching a replacement switch or contact.

I will update when this is done.

Red & Teds Road Show, Williams Pinball Machine (1994)

Location: Broomfield, CO

Symptoms: Delivers too many balls to the shooter lane.

In this era of pinball machine, the ball trough is monitored by infra-red emitters (LEDs) and detectors (photo transistors).  The detectors are on one side of the trough, the emitters on the other side of the trough.  The game senses the ball when it breaks the beam of light between the two.

The owner had suspected faulty opto boards and had replaced them to no avail.

The test diagnostic (“switch edges”) showed that the Trough Jam opto was not working.  It said there was a trough jam all of the time, even when no balls were present.  This caused the firmware to think the ball was jammed and to try shooting it again into the shooter lane.

Switch Matrix (click for larger and clearer)

Even though the owner had replaced the opto boards, I wanted to start at the beginning and make sure it was working. I checked the signal at the collector of the photo transistor while the owner blocked the light in the trough.  When the light was allowed to hit the detector, the collector measured 12 volts (or close to it).   When the light was blocked, it measured near 0 volts.  This is correct.

Photo-transistor schematic; the red dot indicating the measurement point.

At this point, I thought it would be a good idea to check the other switches in the same row and column as the “Trough Jam” to see if there was a wiring or MPU problem in the switch matrix.  Several other switches in the row did not work.

We spent some time tracing the row wire through the various bundles, not an easy task when 40-50 wires are tie-wrapped together.  The row and column wires are daisy-chained from one switch to the next, zig-zagging across the playfield. We found it broken at the White Standup switch.

I re-soldered the wires to the switch and everything worked.

While the switch edges diagnostic was running, we discovered and unrelated intermittent switch.  We found it easily at one of the eddy current sensors because the LED on the sensor board would blink whenever the connection was lost.  One of the wires was pulling out of the connector.  I tie-wrapped the top of the connector to act as a strain relief and hopefully it will hold.

Counterforce Pinball Machine, Gottlieb

Location:  Highlands Ranch, Colorado

Symptom: No Sound

The owner of this machine had sent both the original CPU board and the Sound board to a pinball repair company located in Illinois.  The owner had found this company listed on E-bay.  He said neither board worked when he received them back.

The owner also had a after-market CPU board made by Ni-Wumpf installed in the game.  It operated without problem (although without sound). So we used Ni-Wumpf to figure out why the sound board wasn’t working.

After checking supply voltages, I traced the audio signal with my oscilloscope.  I could see the audio coming out of the sound generator chip and going into the audio amplifier chip.   But there was nothing coming out of the amp chip (LM380N).  I verified that the output circuit wasn’t shorted, so everything was pointing towards a bad LM380N.   I would need to need to take the board back to my office for repair.

Next, I turned my attention to the original Gottlieb Systems 80 CPU board. The fact that the Ni-Wumpf would work with the game, indicates the pinball machine itself was not the cause of the original CPU board not working.  The Illinois pinball repair company was blaming the slam-tilt circuit for the board not working.  We checked the slam-tilt wiring and it was not at fault.  In fact, someone had soldered the slam-tilt wires together so that it would never activate.  The symptom was that the game wouldn’t boot-up and would cycle the Tilt Relay about once per second. Searching the internet revealed that this is usually associated with a bad or corrupt ROM.

Obviously, neither board was fully tested before leaving the pinball repair company in Illinois.  Also, the ICs they replaced were sanded and painted.  In my opinion, no reputable repair service will do this.  I can’t even imagine why they do this.  The sanding can cause a huge build-up of static electricity, which will damage the chips.  I also noticed the sound board card edge connector was sanded.  We don’t know if the other repair company did this, but someone had sanded through the tin and nickel plating, which doesn’t oxidize very fast, down to the bare copper which oxidizes rapidly like a penny does.  Oxidation will cause the contacts to develop a high electrical resistance and cause lots of intermittent problems.  The best way to clean a circuit board edge connector is to use a pencil eraser and follow up with some denatured alcohol to remove any oil residues.

We didn’t do any further testing with the CPU board because the owner wants the other pinball repair company to make it right.

I brought the sound board back to my office.  I purchased an LM380N at JB Saunders in Boulder, and de-soldered the faulty chip and replaced it.  I connected a power supply to the board and with a signal generator, injected a signal into the input and verified the amplified signal was on the output.  The datasheet states the LM380 has a voltage gain of 50. 0.2V input was amplified to 10V on the output.

I shipped the board back to the owner.  Before reinstalling the sound board, I had him check to make sure there was no voltage on the speaker wire.  The presence of a voltage would indicated the speaker wire was shorted someplace and would probably damage the sound board.  He reinstalled the sound board and everything worked.

Police Force, Williams Pinball Machine

Location: Littleton, Colorado

Symptoms:  Weak flipper, lower playfield general illumination not working.

I started with the flipper.  I checked the mechanical aspects of the flipper by manually turning it. Then I checked the end-play by lifting it up and down, and tried to rock it back and forth to check whether the flipper bushing should be replaced.  Mechanically, everything seemed fine.

Next I turned to the electrical aspects of the flipper.  Flippers of this type have two coils wrapped around the solenoid coil bobbin.  One coil provides a strong magnetic field for starting the movement of plunger (slug) into the solenoid.  The other coil provides a weaker magnetic field for holding the plunger once it has been drawn inside the bobbin.  The force required to hold the plunger is less than what it takes to draw it in.

When the flipper button is pressed, both coils are initially energized.  Once the flipper is at it’s ending position, it opens a switch that turns off the more powerful coil and leaves the weaker coil energized.  This allows the flippers to be strong, but prevents them from burning up if someone were to hold the flipper button.  If power were applied constantly to the more powerful coil, it would overheat and start burning.

The switch that opens when the flipper reaches its end position is called the End of Stroke switch (EOS).  I check the EOS switch with the power off and the flipper in its normal resting position with my ohm-meter, and it was “open”, when it should have registered a short.  I cleaned the contacts with some 440 grit sandpaper, and adjusted the contacts to make sure they were closing when the flipper was at rest.

Drawing of flipper unit from the Police Force manual, showing the End of Stroke switch.

I rechecked the switch contacts with the ohm-meter and they were working properly.  We powered-up the machine to verify the flipper was working fine.  Basically, since the switch wasn’t closing, the flipper was only running with the weaker coil.

Next I took a look at why all of the General Illumination (GI) lights in the bottom half of the playfield were not working.  The GI lights are the ones that stay illuminated all of the time and light up the plastics and the playfield areas so that you can see the ball.

First I checked to make sure no voltage was present at one of the light sockets.  Although it was a remote chance, I wanted to be sure that it wasn’t just a case of the lights being burned out (which could have happened if there was a short with a higher voltage somewhere else in the machine).  There was no voltage (be sure to measure on AC scale).  I checked where the power was coming from the Backbox Interconnect board, and there was 6.3 volts there.  So somewhere between the backbox and the playfield, the voltage was getting lost.

I tipped the playfield all of the way up and found the GI Relay on a small circuit board at the very bottom edge.  The connectors that connect the wires to the board were burnt and falling apart.  The connector on the circuit board was burnt as well.

Connector failure is a common problem with GI lighting in pinball machines. Oxidation builds up on the connector pin, or the crimp, and causes the resistance of the connection to go up.  This causes the connector to heat up until it fails. Because each machine and manufacturer uses different types and sizes of connectors, it’s difficult to to keep connectors on hand.  In this case, I didn’t have replacements with me.

The owner didn’t want to wait to get the proper connectors and asked that I solder the wires directly to the circuit board.  I did so, and the lights all worked fine after that.  Normally I am a purist about having the connectors fixed properly, but in this case the connectors only served to make the board replacement easier, which is unlikely to ever need replacing.

GI lamp relay board.

We checked and replaced several burned out lights.  The game was working well and in good condition.