Black Jack Pinball Machine (Bally, 1977)

Location: Cheyenne, WY
Symptom: Wouldn’t boot up.  Battery leaking.

Before powering up, the first thing I did was to remove the leaking NiCad battery from the MPU board.  Fortunately, it hadn’t damaged the PCB traces.  I replaced the RAM with an anyPin NVRAM module.

The machine wouldn’t boot when power was turned on. I checked the power supply first, since the power supplies in this era of Ballys are notorious for failing.  All voltages were good.

The light on the MPU board flashed 7 times on power-up which indicated that most of the boot sequence was executing, but it was stopping just short of going into “Attract Mode”.

With my oscilloscope, I started probing around the MPU board.  The processor was running and there was activity on the address and data buses.  There was no activity on the IRQ (interrupt) line (pin 4 on U9).  There are two sources (that I’m aware of) for interrupts.  One is the display, the other is the AC zero crossing detector.

I checked the display interrupt generator, which is a 555 timer at U12.  There were pulses on pin 3.

Next I checked the zero crossing detector and found no pulses there.  The problem ended up being the 2.0K resistor (R113) at the input to the board, and is the top part of a voltage divider in conjunction with another 2K resistor at R16.  Fortunately, Radio Shack still carries resistors (although the guys working there have no idea what a resistor is or what it does).  We were able to get a 2.2K which is close enough.

Once the resistor was replaced, the machine booted up just fine.

 

Creature from the Black Lagoon Pinball Machine (Bally/Midway, 1992)

Location: Centennial (Denver), Colorado.
Symptoms: Blows fuse on power up.

When powering up the machine, the F114 fuse (8 amp) would blow.  This fuse powers the lamp matrix as well as the CPU +12 volt circuit through a downstream fuse (F115), which is used for the switch matrix.  So when I first power up the machine, the CPU was booting but none of the lights were flashing and the switches on the coin door were unresponsive.

I disconnected all of the lamp matrix connectors from the Power Driver Board (J133 through J138) and powered up the machine, and the fuse blew again. Since all of the connectors were disconnected and fuse F115 wasn’t blowing, the problem had to be in the power supply itself.  There are only two possibilities, a shorted bridge rectifier or a shorted capacitor (rare).  I check the bridge rectifier and it was shorted between “AC” and “+”.  I had a spare bridge rectifier on hand and replaced it.

The machine powered up as normal this time.  A lot of the matrix lamps weren’t working.  I replaced a bulb near the flippers and it still didn’t work.  I thought maybe a row or column driver had failed.  So I ran the test for individual lamps and marked a copy of the matrix with an “X” if the lamp wasn’t working.  No clear pattern emerged to indicate a row or column problem.

So I started at the first bulb in the test and looked at each one.  It turned out that most were burned out.  Also, I found a broken wire for Row 1 of the matrix.  Reconnecting that got about 6 more lights working, including the first bulb I had replaced where replacing it didn’t help.  It’s a tedious process, but in the end the machine looked and played well. I probably replaced two-dozen bulbs.

Space Invaders Pinball Machine (Bally, 1980)

Location: Near Morrison, CO.
Symptoms: Blows fuse (F4).

The machine would immediate blow the fuse (less than 1 second) upon powering up.  Fuse F4 supplies the 43 volt solenoid circuits which are prone to broken wires, shorted coils, etc.  So, I expected to find a short somewhere on the playfield.   I isolated the power supply by removing all of the connectors except for J2 (cabinet) which supplies the wall AC power to the power supply, but this connector also supplies solenoid power to the knocker and the coin door.  The fuse still blew.  I checked the cabinet wiring to make sure there was no short, then focused on the power supply itself.

It turned out to be a shorted bridge rectifier between the AC and the minus (-).  I brought the power supply back to my shop for repair.  I looked up the part number for the bridge and found it on Marco’s site.  For better or worse, the bridge I received was slightly larger.  Not only were the pins further apart, it was also thicker.

New bridge rectifier (black square) above an original working bridge rectifier just below it.

This posed a problem as there are two bridge rectifiers in the circuit and both are mounted on the bottom side of the PCB and are heat-sinked against a metal bar on the power supply chassis.  If one is thicker than the other, one will be heat-sinked, the other will not.

I decided to shift the bar over, so that existing bridge would contact the bar and the new bridge would go directly to the chassis.

With the metal bar, both rectifiers will contact the chassis when the board is remounted.

I added some new heatsink grease to both bridges.  I powered the circuit and all was fine.  This power supply was only used on two machines, KISS and Space Invaders.

Back at the customer’s location, the game powered up and worked fine.  I replaced a few burned out bulbs.  The NiCad RAM backup battery mounted on the CPU board has partially failed. I am debating whether to replace it with a 1 farad super cap, or the typical 3 cell AA holder.  The super cap requires the machine to be powered up periodically so that it can recharge.  The AA batteries don’t require recharging, but there is no nice place to put the battery pack and they have to replaced every few years.

 

Twilight Zone Pinball Machine (Bally, 1993)

Location: Littleton/Denver, CO.
Symptoms:  Flipper problems, ROM checksum error, Proximity Sensor error.

I started with the ROM checksum error.  I re-seated the game ROM in U6 and the other socketed parts, with no improvement.  I programmed a new 27C040 with the game code (decided to try the 9.4H version) and replaced the ROM and the problem was solved.  I verified the code in the old ROM and there were several bits that had reverted back to 1, which was causing the checksum error. This probably caused the game to lock up occasionally, which was one of the complaints.

The proximity sensor senses when a normal metal ball is delivered to the shooter lane (as opposed to the Power Ball which is made of ceramic).  It was simply out of adjustment and not located close enough to the ball to sense it.

The flippers had the most problems.  Neither of the left flippers were working properly.  The top flipper was kicking out, but not holding and the bottom flipper was vibrating and buzzing and weak.  At first I thought the two problems were related and that there may have been a driver problem on the Fliptronic board.  But that wasn’t the case.

The upper flipper had a broken wire on the holding coil. I resoldered it the coil and it solved that problem.

Fliptronic I Flipper Button Opto Board

The lower flipper had a more difficult problem to find.  I hooked the oscilloscope up to the flipper driver output of the Fliptronic board.  It was rapidly pulsing off and on.  When I disconnected the flipper connector, the problem went away and there was steady power to the connector.  I checked the coil resistance and found no problems.  It turned out to be the flipper button opto board.

Normally when pressing the flipper button, the optical path opens and the phototransistor begins pulling the signal down to ground from 12 volts.  When the voltage falls below 5 volts, it triggers the flipper driver via the processor.  A good opto circuit will pull down to below 1 volt.  This was only pulling down to about 4.8 volts, which was too close to the threshold of 5 volts.  When the flipper engerized, the ground probably shifted a little causing the circuit to think the voltage had risen above 5 volts, thus shutting the flipper off. As soon as the flipper shut of, the voltage would fall back below 5 and energize the flipper again.  A vicious circle, which caused the output to pulse off and on very rapidly.

I tried cleaning the opto interrupter, but that didn’t help.  The opto interrupters for this board are no longer available (as far as I can tell).  The only option was to replace the board.  Great Lakes Modular offers a totally redesigned flipper button board that utilizes magnetic sensors instead of optical. The pinball machine owner opted to give it a try.  I ordered one and installed it.

The board needs to be adjusted once it’s installed.  The LEDs on the board really help this process.  However, to adjust it, you need to slide the magnet into different positions and I found it really sensitive.  Just a 1/16″ movement will cause it to go out of adjustment.  Great Lakes recommends taping the magnet after getting it adjusted.  I opted to glue it.  We’ll see how long it lasts. Once adjusted, it had the same feel and response as the right side flipper button.

 

Aladdin’s Castle, Bally Pinball Machine, 1976

Location: Longmont, CO.

Symptom: Pinball machine wouldn’t reset.

I visually checked the most likely relays and contacts: Game Over, Coin, and Credit.  After not finding any problems with the relays, I checked the switches on the score motor unit.  I noticed that the motor was hot and was obviously energized, but not turning.  The cams rotated freely but the electric motor itself was seized.

I disassembled the motor and managed to get the seized shaft out of the bearing. I cleaned both shaft and the bearing, but there was still some type of corrosion on the shaft that was preventing it from turning freely.  I would have preferred burnishing the shaft with some very fine 0000 steel wool, but I didn’t have any on-hand.  I used some 800 grit sandpaper and removed the corrosion (or whatever it was).  I lubricated the bearing and the shaft so that it slid and rotated freely.

After reinstalling the motor into the scoring unit, the machine reset correctly when pressing the start button.

The scoring motor and switch bank assembly is basically the heart beat that runs an electromechanical game.  Without it, nothing will work.

We (the owner and I) noticed that the Ball In Play lights were not resetting back to Ball 1 during the reset.  I checked the stepper in the backbox and saw that it was sticky, which is a common problem.  It didn’t seem sticky enough that it warranted rebuilding. The Ball In Play stepper unit is a step-up and reset type. The owner cleaned the old lubrication from the contacts and I added a turn on the spring.  The stepper seemed to function fine after that.  I informed the owner that if problems continued with the ball counter, that it would have to be cleaned and re-built.

We replaced some burned out lights on the playfield and talked about playfield care.  I mentioned that a lot of collectors have differing opinions, but that I liked Novus 2 for playfield cleaning and polishing.

As for me, I’m going to start carrying 0000 steel wool in my repair kits for cleaning up motor and stepper shafts.  It has worked well with jukebox restorations I’ve done.

Bobby Orr Power Play, Bally Pinball Machine

Location: Littleton, Colorado.

Symptoms: Two of the displays had digits that were blank (off). General illumination lights on the backbox were not working.

I ran the display self-test to determine the full extent of the display failures.  One digit on the Player 1 score and one digit on the Player 4 score were not working. They were different digits, so it wasn’t a problem with connections from the CPU board.

I started with the Player 4 display.  I disconnected and removed the display from the backbox panel and checked the digit driver transistors with a mulitmeter on the “diode” scale.  The transistors checked OK.  This was a little surprising to me.  So I connected an oscilloscope to the digit drive signal.  It was OK where it was coming into the display board.  There was no signal on the collector of level shifter transistor (Q6 in the diagram).  Surprisingly, the 100K resistor was bad and read “open”.

Schematic showing one of the digit drivers.

I had previously read about the power rating of these 100K resistors being too small as originally designed, but I wasn’t expecting to see a failure with no visual indication of the resistor being over-heated.  I didn’t have any spare 100K resistors with me, but fortunately Radio Shack is still good for some very common parts.

I disconnected and removed the Player 1 display and immediately checked the resistor for the failed digit and it too was bad.  With the resistors from the nearby Radio Shack, I was able to desolder and replace the resistors on-site.  I re-assembled the displays into the backbox and re-tested.  Everything worked fine.

As for the general illumination lights not working on the backbox, this is a common problem and is often related to a connector.  This was no exception.  I traced the non-working branch of lights back to the connector at the power supply board.  A portion of the connector on the PCB had been previously replaced, with a version with slightly shorter pins.  The lights started working with just touching the connector.  I checked the solder connections on the back side of the PCB and cleaned the connector contacts.

As I usually do when I work on a pinball machine, I ran a light test and replaced several bulbs that were burned out on the playfield.

 

Dirty Harry Pinball Machine, Bally/Williams

Location: Denver, Colorado.

Symptoms: Dot matrix display (DMD) flickering and displaying random garbage.  Test Report listed Sound Error.

This machine looked to be in very good and clean condition.

I opened up the backbox to investigate the display problem. There is a wide gray ribbon cable that connects the CPU board to the Dot Matrix Controller Board.  All I had to do was touch the connector where it connects to the display board and the problem went away and never came back. The connector didn’t appear loose.  I disconnected connector from the board, squeezed it from front to back to make sure the connector was making a good connection with the ribbon cable.

This type of connector is referred to as an Insulation Displacement Connector (IDC).  There are small gold plated forks that pierce the insulation in the ribbon cable and make connections with the internal conductors.  Sometimes a little oxidation forms between the the fork and the conductor and squeezing will help restore the connection.  If it’s really bad, the connector can usually be carefully removed and re-crimped on the cable next to the original location.  (To do this correctly, you will need a padded vise to gently squeeze the connector onto the cable without breaking the connector.)

Once the display was working, re-powering the machine indicated there was a Test Report.  This will only display if the the computer has detected a problem.  Viewing the test report indicated a Sound Error.  I went to the test menu and performed a Sound Test.  All of the sounds were working fine.  I powered down the machine and reseated all of the sound EPROMS on the sound board.  Upon powering the machine back up, the Test Report didn’t show up, indicating the problem was no longer present.

The customer asked about routine maintenance and what should be done.  The most important routine maintenance is keeping the machine’s playfield clean.  Every time the pinball hits a pop bumper, slingshot or even the flipper, the friction of the ball accelerating or decelerating on the playfield will cause a microscopic amount of metal dust to come off the ball. After a while, the grayish metal dust accumulates and starts to wear into the playfield. It migrates down into the switch contacts and mechanical parts, wreaking havoc. It leads to all kinds of intermittent and permanent failures.

Likewise, since the microscopic metal dust is coming off the ball, the balls should be periodically replaced. The ball surface develops microscopic pits, which makes the ball rougher, which increases the friction mentioned above, which increases the wear on the playfield, etc.

One quick look at this Dirty Harry pinball machine told me the owner had been keeping it clean.

 

Judge Dredd follow up

Location: Denver, Colorado.

A few months later, I was called back to the Judge Dredd machine mentioned in this previous post.

The thermistor in the power line module had burned out.  I replaced it and tested the machine.  I noticed that the shorted switch-row problem had returned.  The nice thing was, it was a solid failure this time and I was able to track it down.

In my previous post, I mentioned the short would go away if I unplugged J212.  This was the case again, and it deceived me into thinking the short was somewhere along this stretch of wires that heads towards the coin door.   In the switch table in the service manual, Switch 24 is listed as Always Closed.

(The switches and lamps in a pinball machine of this vintage are multiplexed in a grid.  This reduces the complexity of circuitry and wiring.  Rather than having 64 separate wires to 64 switches, by multiplexing, 64 switches can be monitored with just 16 wires.)

Somewhere in the machine, there is a diode connecting Column 2 and Row 4.  It turns out it’s on Coin Door Interface Board, which is were the wires from J212 end up (D2).

What is deceiving is that when a column is shorted to ground, any switch that is closed will show that row to be shorted.  Since switch 24 bridges column 2 and row 4, every switch in row 4 was shown as closed, leading me to believe the problem was in row 4.  But when I closed other switches in column 2, the entire corresponding row would show as closed.  And as a verification, I open the diode at D2 and the remaining switches in row 4 began functioning normally.

Once I determined the problem was actually in column 2, and the symptom indicated it was shorted to ground, I unplugged J205 and J212 to isolate the CPU board from the rest of the machine.  I measured the outputs of each column driver and found the output of U20, pin 17 was stuck at ground.

I replaced the ULN2803 with a new part and everything in the pinball machine tested normal.

 

The Shadow Pinball Machine, Bally/Williams

Location: Erie, Colorado.

Symptoms:  Neither ball diverter was working, drop targets on mini-playfield were sticking.

The ball diverters at on the left and right ramps were simply loose on their shafts.  I tightened up the set screws on the left diverter.  The right diverter was binding a little after tightening the set screws and I determined the arm was slightly bent.  I straightened it and it worked fine.

Right ramp diverter, with rings on either side. (Photo from ipdb.com)

I removed and cleaned the drop targets from the mini-playfield.  They had been lubricated with white lithium grease, and as usual, it had dried and was causing them to stick.

I looked at the Test Report and it reported that the switch on the main playfield drop target was not working.  It was simply a case of the drop target sticking and never engaging the switch.  I removed and cleaned the drop target.

There were a couple of broken wires that I re-soldered to their correct locations; one was a flasher and the other a GI bulb.  I replaced 24 bad bulbs. There are four rings with lighted jewels incorporated into the playfield (see photo above).  They are illuminated with a grain of rice lamp that is hard-wired.  Three of those lights on this machine are out.  Marco has these and will order.  I’m guessing they are glued in place.

The machine also needs a new set of pinballs.   Any pinballs that don’t look shiny and new should be replaced on any machine in order to keep the playfield in good condition.

All in all, just routine maintenance.

Judge Dredd Pinball Machine (Midway/Bally)

Location: Denver, CO (Arvada)

Symptoms: Flipper was stuck, multiple connection problems, neither slingshot working.

Stuck flipper: The flipper was stuck because the end of stroke (EOS) switch was broken exactly at the flipper’s maximum travel point.  The flipper wouldn’t return because it was getting hung up on the broken contact.  For a quick fix, I put a piece of shrink tubing over the end of the contact to lengthen it.  As the tubing cooled, I flattened it with my fingers, which basically made a plastic extension for the contact.  Eventually the switch will need to be replaced, but for now it is working fine.

Connection problems:  There were some connection problems causing balls to be continuously delivered to the shooting lane.  Taking a look at the switch test diagnostics, I determined a whole “row” of switches was shorted to ground (row 4).  After checking every switch location in the row on the cabinet and under the playfield, and not seeing any obvious shorts, I decided to look at the back box.  There I discovered if I pressed on the lower corner CPU, the short would go away.  My initial assumption was that it was something on the CPU board shorting out.  Yet, when I unplugged J212 the problem would disappear.

J212

Row 4 is the end pin on the connector (pin 8). So why does lightly pressing on the CPU board cause something associated with J212 to short/unshort.  I looked all around and traced the wires back and couldn’t see anything.  Unfortunately, I moved something and the short went away and never came back while I was at the customer’s site.  After I left the short returned. On a subsequent visit, the problem had gone away again and couldn’t be found.

Slingshots: The owner didn’t realize that neither slingshot was working.  Both had broken mechanical links from the plungers, one had a broken arm.  Replacement parts were ordered and installed.

Doing one last check of the Test Report, I saw that the EOS switch on the left upper flipper was disconnected.  I found the broken wire and resoldered it to the switch.

The Test Report also revealed that one of the ball trough opto switches wasn’t working.  Using a cell phone camera, which can see the infrared light of the opto switches, I determined that one of the IR LED’s was not illuminated.  I checked continuity and didn’t find any problems with the circuit board.  The LED was burned out.  After a discussion with the owner who assured me that the game is working fine, we decided to leave it as is.  There are 7 opto switches monitoring the ball trough and it was of the ones in the middle.  My guess is since the CPU knows it’s bad, it can work around it.  If it causes a problem, there is a very nice after-market IR LED board available which has several design improvements.

And finally, the entire game had intermittent power.  I quickly determined that the line cord was not plugged securely into the rear of the game.

Other than just a few test games, I’ve never played Judge Dredd.  It seems like an interesting and challenging game.

This post has a follow-up here.