Section 2 - Connectors and other Intermittent Problems 

This is section 2 of a multi-part document.  Go to my System 3-7 Resources page for the repair guide index.  Lots more pinball at Mark's Pinball Page!

(page last updated 1/20/04)



While electro-mechanical games (in theory) will operate forever if properly maintained, first generation Solid State machines have a large number of components that have a finite life span.  And woe to the owner of a Disco Fever, because most of the components in his machine have reached or exceeded their expected life span.

The majority of these machines are over 20 years old as of this writing (2002) and have seen years of hard service in less than ideal conditions.  Dirt, heat, moisture and smoke have taken their toll on the metal surfaces of the machine's connectors.  These conditions and temperature changes, which result in expansion and contraction of the solder joints, have also lead to microscopic cracks in solder joints which can cause a working machine to freeze in its tracks at the oddest moments.

This section deals with "intermittent" problems, those nasty bugs that seem to only crop up 5 minutes after your party has started.



1. Causes of Intermittent Problems

The symptom of an intermittent problem is usually a random reset or the game shutting down during play or attract mode.  A game may also seem to take on a life of its own, making random sounds, scoring invisible points, just going "crazy".

These problems are usually caused by either one of three problems, a faulty power supply, a bad coil or a connector failure.

1.1 Determining what's causing your problem

Intermittent problems are not the easiest to track down.  There is a list of the "usual suspects" and your best course of action is to start with the most common problem and work you way down the list to the least common.

1.2  Attempt to isolate your problem

The first question that needs to be answered is "does your problem occur only during game play or does it occur while the game is in attract mode or does it occur in both circumstances?".

If your game resets or locks up during game play, it could be any one of the three main causes (coils, power supply, connectors), with power supply problems and coil problems being at the top of the list.  

Games that reset or lock up while in attract mode are usually have connector related problems or line voltage problems.

My rule of thumb is that if the game resets or locks up in attract mode, then its a usually a connector problem and I tackle them first.  If it resets or locks up only during game play, it's a diode or power supply problem and I work back from the coils to the power supply.

Notice that I used the word "usually" and "could" in the above descriptions.  In my experience, 80% of the intermittent problems can be isolated as I've described, but your game could be one of the 20% that is experiencing another problem.  

1.3 Flipper Coil problems

Probably the easiest problem to diagnose and fix.  If your game resets when you press a flipper button, then you have a blown diode on that flipper coil.  Games of this era use purely electro-mechanical flippers, so there are no circuits or boards to be investigated (no flip-tronic board here to worry about!).  

An open diode is allowing the reverse voltage caused by the breakdown of the coil's magnetic field back into the games power supply, reeking havoc with the games logic circuitry, resulting in a reset.  

Replace the diode on the flipper coil with a 1N1004 and you'll be back up and running.

1.4 Playfield Coil problems

If your game is resetting during game play, it may be due to an open diode on a playfield coil.  A shorted diode on a playfield coil will usually result in a blown fuse when the the coil is fired, same with a shorted coil itself.

Remove the playfield glass and start a game.  Using you fingers (or the ball), manually trigger each solenoid.  Hit each target and every switch also.  By doing this in a controlled way, you can hopefully isolate the bad coil.

You can also use the solenoid test function to cycle through each solenoid.  Watch the solenoid number displayed in the ball in play display to see which solenoid is firing. If the game resets or blows a fuse during the test, you've isolated your problem.

The only caveat is that sometimes the voltage "pulse" sent to each coil during the test isn't long enough to trigger the problem, especially for the special solenoids (pop bumpers and kickers), which is why you should also perform these tests by hand.

I've run into situations where a single coil firing won't trigger a problem, but two coils firing at the same time will.  If its always the same two coils, replace the coil diodes.  If any combination causes the problem, this usually indicates a power supply problem.

1.5 Power  Problems

Power supplies are covered more in depth in the next section of the guide, but we'll try in this section to determine if the problem lies in the power supply.

1.5.1 Line Voltage

During the summer our area experiences low line voltage levels and I've noticed that games that played fine during the winter will randomly reset during the summer.  The first test you should do is to isolate your game onto its own circuit (nothing else turned on).  

In some houses builders have done strange things with wiring.  In a previous house we owned, whenever my daughter would turn on her hair dryer in the bathroom, we would blow the circuit that the outside Christmas lights were on!  In houses built in the 80s on, basement circuits are on GFI (ground fault interrupt) circuits, as are the outlets in your bathrooms and garage.  Your game in the basement may be on the same circuit as your garage door opener and your master bath.  A sudden drop in line current, say when a motor is first operated, would cause enough of a voltage drop that your game would start to shut down, then come back up when the voltage stabilized again.

If the game operates fine without resetting when its isolated, look at adding an additional circuit for the game.  

1.5.2 Power Supply

If you've gone through the solenoid tests above, and the game comes through flying colors, but still resets during game play even on its on circuit, then its time to look at the power supply.  These games are for the most part over 20 years old, and the life span of the electrolytic capacitors in the power supply has long since be surpassed. 

If your game locks up or resets on a seemingly "random" basis when different solenoids fire and you've replaced the solenoid diodes, then your power supply is suspect.  

Before tackling your power supply, replace the connectors as outlined in section 2.3.  They will be the first to go and need to be replaced no matter what.

There aren't that many components that make up the logic supply portion of a System 3-6 power supply (a few more in a System 7 power supply), so a rebuild is not a big job. Part 3 of the guide covers this in more detail.

2.  Connectors, Connectors, Connectors!

Let me say it again, connectors!  If you are experiencing intermittent problems with your machine, lets say it starts sometimes, then every fourth time you turn it on it locks up with 2 LEDs on, then you are probably experiencing a problem with a connector somewhere in your machines.

2.1  The Interboard Connector

If 95% of all intermittent problems are caused by connector problems, then 95% of connector problems lie in the 40 pin "interboard" connector that connects the driver and mpu boards together.  In section 1.3 I discussed the reasoning behind the split board design, separating the components for easier field maintenance.  In practice this turned out to be an excellent idea, and to this day still makes troubleshooting easier than with a single mpu/driver board (just ask the owner of a System 9 or 11 game).  However the Achilles heal of this design is the 40 pin inter-board connection.  Williams' designers opted to move the entire data and address bus over these pins, as well as the reset, blanking, interrupt and every other critical system signal.

This worked well for the first few years of a machine's life, but after years of service in less than ideal conditions, these connectors would start to get dirty.  Even worse, and the cause of most problems, is that the solder joints on both boards would start to develop microscopic cracks due to constant vibration (in a pinball machine!) and heat and humidity changes.  One micro-second of a disconnect in a data or address line is enough to bring the machine to a halt, the game's program not knowing what to do next.

2.1.1   *** The first thing you ever do when your machine isn't booting! ***

Rule #1 when trouble shooting an early Williams machine is to first "peel" apart the MPU and driver board and then reconnect them.  Do this slowly and make sure you remove all of the screws securing the boards to the backbox.  Each board is held in by six screws., however chances are your boards will not have six screws each, a clear indication that the machine has been worked on before. 

The MPU board sits in a "tray" which somewhat locks it into place.  You'll want to make sure the board is still in the tray when your peeling them apart.  You'll also notice when you're taking the boards apart, how much the driver board flexes during this operation.  The more times the boards are separated, the more chances that a small break will occur in the solder joints of the connectors.

Don't attempt to clean the connectors with anything other than a soft towel.  Using any abrasive on them will create small pockets where more dirt can collect and cause the boards to fail even quicker the next go round.

Once you've peeled the boards apart, just reconnect them again.  Make sure that the MPU board is properly seated in its tray, then from left to right start pushing the driver board back over the pins.  Don't force the board, if it doesn't go on properly, start over again.

Once you've put the boards back together, reattach the boards to the backbox with at least two screws apiece.  Then remove and reconnect all of the header connectors on both boards.

Now power your machine back up again.  You may be pleasantly surprised to see it working again and you can pat yourself on the back for a job well done!

2.1.2  OK, so that worked, but why?

The simple act of removing and reconnecting everything does a simple "cleaning" of the connectors due to the wiping action when you unplug and plug them back together.  A break in a solder connection may also have been nudged just enough that its now making contact.

Could this be enough to do the job?  If the machine is working, then you may just want to leave well enough alone and put the backglass back in and start playing again.  I have had machines that I've done this to once and they've continued to run for two years without a problem.  If you are restoring the machine or doing other major work, I would suggest re-soldering the header pins (see below).

Chances are that the problem will crop up again in a few days or weeks.  If this happens, you should first re-solder the header pins on the MPU board the the connectors on the driver board. If the problem persists, then its time to replace the header pins and driver board connectors.

2.1.3  The "fix" you NEVER, NEVER, and can I say again, NEVER do!

The worse piece of advice you can ever follow with an System 3 through 7 game is to solder together the MPU and Driver boards.  NEVER, NEVER do this.  Why you ask?  After reading the above paragraphs, this would seem like sound advice.  If problems occur because of dirt and bad connectors, why not just solder the things together and eliminate the problem forever?  What you accomplish by doing this is a short term fix that can lead to much larger problems in the future.  You will no longer be able to "swap" boards if you have a problem with either board.  You will also not be able to troubleshoot problems as easy.  Since the boards were designed as two components originally, most all troubleshooting methods involve separating the boards.  No repair facility will accept your boards either, so you better be sure that you can repair them yourself.

2.2  Header Pins - The second thing you do when your machine isn't booting!

The "prongs" on the Driver and MPU boards are known as "header" pins.  They are pushed through the board and soldered on the reverse side of the board.  This pins flex a good deal every time a connector is removed or reconnected.  Temperature and humidity changes  also cause these joints to contract and expand, which over time can result in microscopic cracks occurring.

To insure that the header pins have solid solder joints, you need to remove both the MPU and driver boards from your machine and re-solder each joint by touching your soldering iron to the joint and waiting until the solder melts.

A word of caution!  Make sure that you do not "bridge" any solder joints.  Visually inspect each set of header pins after you finish.

The larger Molex style header pins and the .156 header pins on the power supply are also subject to the same joint cracking problems as the MPU and driver boards.  

2.3  The MPU board Power connector, the overlooked problem child

Connector IJ2 on the MPU board (left side of the board) brings the +5vdc regulated and +12vdc unregulated power from the Power Supply board to the MPU board.  The +5vdc is carried on three wires for good measure, however the +12vdc is only carried on one wire (the top one).  The purpose of the +12vdc is to signal the MPU board that its been powered down and for the reset circuit to shut things down.  If this connector is dirty or loose, it can loose contact for a split second during heavy play (all those pop bumpers going!) and the machine will reset.  The board will also not boot if the +12vdc is not present, so a weak or bad connector here can cause your board not to boot.

I do recommend replacing this connector and housing when you get the chance.  If you're experiencing random resets, replacing these is a must.

2.4  Connectors Housings and Pins

When most people pull connectors off, they tend to grab the bundle of wires and not the housing.  Repeated removal of connectors in this fashion will of course lead to problems.  The wires are crimped to the connectors, not soldered, so the connection is not actually permanent.  Wires can break in the connector and still make intermittent contact.

The connectors, just like the headers, will get dirty over the years.  Machines that have been in storage , especially in damp places, will suffer from corrosion. A good visual examination of the connectors will reveal a lot.  Look for any discoloration which is an indication of excessive heat.  The dirtier a connector pin gets or the more corroded it gets, the resistance will build up which will generate heat.  Any connector pin that shows signs of heat needs to be replaced.

One problem that plagues Williams machines of other eras is burnt GI (General Illumination) connectors.  On System 4 and 6 machines, Williams removed all GI connections from the Power Supply board and hard wired them right to the fuse block.  So if somebody tells you to check for burnt GI connectors on your Firepower, start looking somewhere else for advice.

System 3 machines however did route the GI power through the power supply board.  And to make matters worse, they pushed the GI through the .156" header connectors, not the larger Molex connectors like later generation machines.  These tended to burn out very early in the life of a System 3 machine, leading to some strange owner/operator repairs. 

2.5  In Summary

To summarize, connectors should be the first place you look when you're having booting or intermittent reset problems.  If the act of peeling apart the driver and MPU boards corrects your problem, then I would suggest resoldering these connectors the next time the problem crops up.  These connectors have all out lived their life spans and are on borrowed time.  

Should you replace the interboard connectors no matter what?  There are some folks out there who will tell you to do this even if your machine is working.  I follow a simpler philosophy, if it isn't broken, don't fix it. However, one caveat to that is that I do highly suggest that you resolder all of pin connections to your boards when you have the board on the bench.  If your machine stops booting on a regular basis and you can fix it via the "peel" process, then its time to replace the connectors.

3.  Board Sockets

The ROM and CPU sockets on your boards can also cause intermittent problems.  Especially troublesome are the "Scanbe" brand sockets used on a number of System 4 and 6 boards.  They can result in the same symptoms as a bad interconnect board; random resets and wild game behavior.  Section 4 of this guide, MPU troubleshooting, section 2.2.12 covers this is more detail.


Go to Part 3, "Getting the Power"

Back to Mark's Pinball Page