Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two
by cfh@provide.net, 03/18/02.
Copyright 1998-2002 all rights reserved.

    3a. When things don't work: Removing the Driver Board
      The majority of electronic repairs will be on the WPC Power Driver board. To do any repairs to the driver board, it must be removed from the game. Yes, there are seemingly an endless array of connectors that will have to be dealt with. Fear not, all are keyed so they can't be plugged into the wrong place (in most cases!). For confidence and simplification, always label the connectors as they are removed. Sure, this is probably unnecessary. But if there are any problems, the idea that I might have incorrectly plugged the connectors can be eliminated. It only takes a minute, and there is never any doubt about what goes where.

    Using a mark-all "Sharpie" pen, label the sides of all the connectors
    as they are removed.

    label the connectors

      Use a mark-all "Sharpie" pen to label the connectors. The side of each connector has room for writing. After the connectors are all marked and removed, loosen the phillips head screws that hold the driver board in place. The screws don't have to removed all the way! Only loosen them. The board has slots for all the screws, so the board will lift up and out of the backbox.

      Note: some connectors are "parallel". That is, they have the same keyed pin configuration so as many as three plugs, can be switched around. To minimize this confusion, again just mark the plugs with a Sharpie as they are removed.


    3b. When things don't work: Replacing Components
      If a bad component has been found, now comes the hard part; replacing it! Transistors, bridge rectifiers, and most chips are not socketed. They are soldered directly into the driver board. Care must be taken when replacing a bad component.

      Please see http://marvin3m.com/begin for details on the basic electronics skills and tools needed when replacing circuit board components.

      When replacing components, the object is to subject the board to the least amount of heat as possible. Too much heat can lift or crack the board's traces. Too little heat and the plated-through holes can be ripped out when removing the part. New circuit boards are too expensive to replace. So be careful when doing this.

      To remove a bad component, just CUT it off of the board, leaving as much of its original lead(s) as possible. Then using needle nose pliers, grab the lead in the board while heating it with the soldering iron, and pull it out. Clean up the solder left behind with a desoldering tool.

      When replacing chips, alway install a socket. Buy good quality sockets. Avoid "Scanbe" sockets at all costs! A good machine pin socket is desirable.


    3c. When things don't work: Checking Transistors and Coils (stuck on coils and flashlamps)
      If a coil is "stuck on" when the game is turned on, a shorted driver transistor could be cause. If a coil does not work (and the fuses are good!), an open driver transistor could be the cause. This section will help diagnose this.

      What do the Driver Transistors Do?
      Basically, a driver transistors completes each coil's path to ground. There is power at each coil, all the time. The driving transitor is "turned on" by the game's software, through a TTL (Transistor to Transistor Logic) chip. When the transistor is turned on, this completes the coil's power path to ground, energizing the coil. Driver transistors also work the CPU controlled lamps and flash lamps, causing a lamp to "lock on".

      Sometimes these driver transistors short "on" internally. This completes a coil or flash lamp's power path to ground permanently, making it "stuck on", as soon as the game is turned on. Also a shorted pre-driver transistor, or shorted TTL chip (which controls the transistors) could be the problem (though a shorted driver transistor is the most common cause). To fix this, the defective component (and perhaps some other not defective, but over stressed componets) will need to be replaced.

    TIP36 and TIP102 transistors on the driver board.
    driver board transistors

    TIP102 transistors, the small 2N5401 pre-driver transistors,
    and the coil diodes on the driver board.

    TIP102 and pre-driver 2N5401 transistors

      There are basically four types of driver and pre-driver transistors used on a WPC driver board:

      • TIP36c (PNP, NTE393): used for solenoid numbers 1 to 8. High power transistors used for more powerful solenoids (and the flipper, on their initial "flip" on the Fliptronics board).
      • TIP102 (NPN, NTE2343): used for solenoid numbers 9 to 28. Low power solenoid and flash lamp drivers, used for most devices (and for the flippers on their "hold" circuit on the Fliptronics board). Numbers 9 to 16 are used for low power solenoids, number 17-20 for flash lamps, and number 21 to 28 for general purpose solenoids or flash lamps. TIP102's are also used to switch GND on for any particular lamp row.
      • TIP107 (PNP, NTE2344): used to drive the CPU controlled lamp (columns) on the playfield. The TIP107 switches the +18 volts on for any particular lamp column.
      • 2N5401 & MPSD52 (PNP): used as a pre-driver for the TIP102 transistors. 2N5401, MPSD52 and NTE288 are all equivalent transistors.
      • 2N4403 (PNP, NTE159): used as a pre-driver for the Fliptronics board.

      Driver Transistor Operation.
      As described above, the main driver transistor (a TIP102 or TIP36) completes the coil or flash lamp's power path the ground, energizing it. But there are other components involved too!

      Each driver transistor has a "pre-driver" transistor. In the case of a TIP102 (the most common WPC driver transistor), this is a smaller 2N5401/MPSD52 or 2N4403 transistor.

      If the main driver transistor is a TIP36c, this is pre-driven by both a TIP102 and a smaller 2N5401/MPSD52 or 2N4403 transistor. The bigger TIP36c transistor is an even more robust than the TIP102, and controls very high powered, high use coils (like the flippers).

      Then before even the smaller 2N5401/MPSD52 or 2N4403 pre-driver transistor, there is a TTL (Transistor to Transistor Logic) 74LS374 chip. This is really the first link in the chain. This is what in affect turns on the smaller 2N5401/MPSD52 or 2N4403 pre-driver transistor, which then turns on the TIP102 (which then turns on the TIP36c, if used for the coil/flash lamp in question), and energized the device.

      This series of smaller to bigger transistors is done to isolate the hi-powered coil voltage (50 volts), from the low-power logic (5 volts) on the driver board. Also the 74LS374 chip (operating at +5 volts), which really controls the transistors, can not directly drive a high power TIP102 or TIP36c transistor (which is controlling 50 volts).

      If ANY of these components in the chain have failed, a coil/flashlamp can be stuck on, and will energize as soon as the game is powered on!

      I have a Stuck-on Coil (or Flashlamp), What should I Replace?
      The following procedures will test the driver and pre-driver transistors in question. If either is bad, it will need to be replaced. When replacing either a driver or pre-driver transistor, replace them both (or in the case of a TIP36, replace the TIP102 and smaller 2N5401/MPSD52 or 2N4403 transistor)! A shorted transistor will cause the other transistors in the link to be stressed, and they should all be replaced.

      Inside the front cover of the game manual is a list of each coil used in the game. Also listed are the driving transistor(s) for each coil. Use this chart to determine which transistors could potentially be bad. Also use the schematics.

      If after replacing the driver transistors the coil/flashlamp is still stuck on, then replace the TTL 74LS374 logic chip. The TTL 74LS374 can also go bad (though it is not real common).

      A Coil just Does Not Work - What is Wrong?
      Driver transistors can go "open" too. This means all the logic prior to the open transistor could be working fine, but the coil will not energize. If there is power at the coil, this is something to consider (but first see the test procedures below to make sure the coil itself is actually OK).

      Do the Transistor Test Procedures work 100%?
      In short, no. But they do work about 98% of the time, and are an excellent starting point. But yes, a transistor can test as "good", but still be bad. The DMM test procedures test the transistors with no load. Under load, a transistor could not work.

    Testing a transistor on the driver board. Note the DMM is set to
    the diode position, and one lead is connected to the metal tab on
    the TIP transistor. The two outside leads are then tested.

    testing a transistor, board installed

      Transistor Testing procedures using a DMM.
      If the driver board is out of the game for some reason (like to fix the burnt GI connector pins), test all the transistors. It only takes a moment, and will ultimately save time. To test a transistor, a digital multi-meter (DMM) is needed, set to the "diode" position. NOTE: testing transistors with a DMM is not 100% fool-proof. A transistor can test as "good" and still be bad (rare, but it does happen!).

      Testing Transistors INSTALLED in the WPC driver board.

      • TIP36c: Put the red lead of the DMM on the metal tab of the transistor. Put the black lead of the DMM on each of the two outside legs of the transistor. A reading of .4 to .6 volts should be seen. Put the black lead on the center transistor leg (collector) and the red lead on the metal tab, and a zero reading should be seen. Put the black lead of the DMM on the left/top (base) leg of the transistor. The red lead on the center transistor leg should show .4 to .6 volts. The red lead on the right/bottom leg should be .2 volts. Any other value, and the transistor is bad and will need to be replaced.
      • TIP102: Put the black lead of the DMM on the metal tab of the transistor. Put the red lead of the DMM on each of the two outside legs of the transistor. A reading of .4 to .6 volts should be seen. Put the red lead on the center transistor leg (collector), and a zero reading should be seen. Any other value, and the transistor is bad and will need to be replaced.
      • TIP107: Put the red lead of the DMM on the center leg or on the metal tab of the transistor. Put the black lead of the DMM on each of the two outside legs of the transistor. A reading of .4 to .6 volts should be seen. Put the black lead on the center transistor leg (collector) and the red lead on the metal tab, and a zero reading should be seen. Any other value, and the transistor is bad and will need to be replaced.
      • 2N5401, MPSD52, 2N4403 (pre-drivers): Put the black lead of the DMM on the center leg of the transistor (note this transistor doesn't have a metal tab). Put the red lead of the DMM on each of the two outside legs of the transistor. A reading of .4 to .6 volts should be seen. Any other value, and the transistor is bad and will need to be replaced.

      Testing Transistors NOT INSTALLED.
      Only the TIP36c will test slightly different out of circuit. The other transistors will test the same as described above. All transistors are laying on the workbench with their "face" (side with the markings) up, and metal tab away from you. Orientation is BCE (base collector emitter), from left to right for the TIP transistors. Orientation for the small plastic transistors is EBC (emitter base collector) with the flat side up.

      • TIP36c: Put the black lead of the DMM on the left (base) leg of the transistor. Put the red lead of the DMM on each of the two other legs (center and right legs) of the transistor. A reading of .4 to .6 volts should be seen. Put the DMM leads on the metal tab and the center transistor leg (collector), and a zero reading should be seen. Any other value, and the transistor is bad.

      Most often transistors short when they go bad. This will usually give a reading of zero or near zero, instead of .4 or .6 volts.

      Testing Coils and Transistors; a Systematic Approach.

      If a coil is not working, the following approach is a good one to take. It starts with the easiest test first; using the internal WPC diagnostics. Then the tests moves to the coil itself, and goes back towards the driver board. This makes the chain smaller, and gives a very systematic approach to finding the problem.

    Pressing the "start game" button on the outside of the
    cabinet during the Solenoid Test gives important information.
    In this example (the Auto Plunger coil), it shows the coil's
    wire colors, the board connectors/pins used, the fuse rating
    and position, and the transistors that drive this coil. Note
    Q72 is a TIP36 transistor with Q60 (a TIP102) as a pre-driver,
    and Q56 (a MPSD52) as a pre-driver to the TIP102.

    solenoid test

      Testing Transistors/Coils, Driver board installed in a (near) WORKING game, using the Diagnostics Test.
      If the game powers on, the WPC diagnostics can be used to test most devices.
      • Press the "Begin Test" button inside the coin door.
      • Select "MAIN MENU: TESTS".
      • Select "TEST MENU: SOLENOID TEST".
      • Use the "+" and "-" buttons to move the test from coil to coil. Each coil should fire. (Note the coin door interlock switch must be held in on 1993 and later games. Otherwise the coil 50 volts will be turned off, and the coils won't fire. Also make sure the "REPEAT" portion of the test is used. This can be changed using the "Begin Test" button.)
      • Press the "help" button. The game's start button during the coil test wil give more coil information including coil wire colors, Driver board connector and pin numbers; related fuse number; Driver board transistor and pre-driver transistor numbers.

      Solenoid Doesn't Work during WPC Diagnostic Tests.
      If a solenoid doesn't work from the diagnostic tests, here's what to check. Turn the game off before doing this.
      • Check all the fuses on the driver board. A non-working solenoid could be as easy to fix as just replacing a fuse.
      • Find the solenoid in question under the playfield. Make sure the wire hasn't fallen off or become cut from the coil (a very common problem).
      • If the above is correct, make sure the winding of the coil haven't broken off from the solder lugs. If one has broken, it can be re-soldered. Make sure the painted enamel insulation is sanded from the wire before re-soldering.
      • Check the coil diode (for any other pinball game, this would be the next step). The coil diode for all games (except WPC) are attached right to the coil, with the banded side of the diode connecting to the power side of the coil. On WPC games however, Williams moved this diode to the power driver board for all coils but the flipper coils. This increases reliability as the diode is not subject to the jarring and heat a coil can produce. It also eliminates the need for the operator to know which coil wire goes to the banded side of the diode when replacing a coil! On a WPC game, these coil diodes are mounted on the driver board next to the transistor that drives each particular coil.

      Quick and Dirty TIP102 Transistor Testing.
      There is an easy way to test TIP102 (only) transistors. This procedure takes about 20 seconds to test all the TIP102 transistors:

      • Make sure the game is off.
      • Put the DMM (digital multi meter) on ohms (buzz tone).
      • Put one lead on the ground strap in the backbox.
      • Touch the other lead to the metal tab on the TIP102 transistors.
      • If zero ohms (buzz) is indicated, the transistor is bad! (shorted on)

      The Coin Door Interlock switch.
      In the middle of Twilight Zone's production in 1993, Williams added a coin door interlock switch. This turned off the power to all the coils when the coil door was opened (for safety reasons). On 1993 and later games with this interlock switch, make sure the coin door is closed when testing coils!

      Failed Coin Door Interlock switch.
      Yes it does happen. The coin door interlock switch can fail, or does not get pushed in enough when the coin door is closed. This will prevent voltage from getting to the solenoids. If none of the solenoids work, and the fuses are good, check the coin door interlock switch for problems. A sure sign of this is the Driver board solenoid power LED's will NOT be lit if the coin door interlock switch is not closed! The interlock switch opens the coil power coming from the transformer, which is way before the power gets to the Driver board's fuses and power circuits.

      Testing for Power at the Coil.
      Most pinball games (including WPC) have power at each and every coil at all times. To activate a coil, GROUND is turned on momentarily by the driving transistor to complete the power path. Since only ground (and not power) is turned on and off, the driving transistors have less stress on them. With this in mind, if we artificially attach a coil to ground, it will fire (assuming the game is turned on).

      • Turn the game on and leave it in "attract" mode.
      • Lift the playfield.
      • Put the DMM on DC voltage (100 volts).
      • Attach the black lead of the DMM to the metal side rail.
      • Touch the red lead of the DMM on either lug of the coil in question.
      • A reading of 20 to 80 volts DC should be indicated. Switch the red test lead to the other lug of the coil, and the same voltage should be seen again. On flipper coils, test the two outside lugs of the coil. If no voltage reading is shown, no power is getting to the coil. On a two lug coil, if there is only voltage at one lug, the coil winding is broken. On 1993 and newer WPC games, make sure the coin door is closed!
      • If no power is getting to the coil, a wire is probably broken somewhere. Trace the power wire.

      No Coil Power, Fuse is Good and No Broken Wires.
      I recently had a problem on a Safe Cracker (WPC-95) where none of the low power (20 volt) coils worked. It was very frustrating; the fuse was good, and power was getting to the Driver board, but not out of the driver board and to the coils.

      It turned out that the capacitor that filters the DC voltage after the bridge rectifier on the Driver board had a cracked solder pad. This prevented the voltage from getting any further than it's associated bridge rectifier (I should have known; the +20 volt LED on the Driver board was not lit!). To fix this, I soldered jumper wires from the bridge to the capacitor, as outlined in the below Game Resets (Bridge Rectifiers and Diodes) section.

      Testing the Coil and the Power Together.
      This test will show if the power and the coil are indeed working together:

      • Game is on and in "attract" mode, and the playfield lifted. On 1993 and newer WPC games, coin door is closed.
      • Connect an alligator clip to the metal side rail of the game.
      • Momentarily touch the other end of the alligator clip to the GROUND lead of the coil in question. This will be the coil lug with the single wire attached (usually brown). On flipper coils, this is the middle lug (the power wire on most coils is usually the thicker violet or red wire). This works on both Fliptronics and non-Fliptronics WPC games.
      • The coil should fire (if the alligator clip is accidentally touched to the power side of the coil, the game will reset and/or blow a fuse, as the solenoid high voltage is being shorted directly to ground).
      • If the coil does not fire, either the coil itself is bad, or the coil's fuse is blown and power to the coil is not present.

      Testing the TIP102 Transistor and Wiring to the Coil.
      If the coil fires in the above test, there may be a transistor problem. The TIP102 transistors can be tested this way. Only do this for the TIP102 transistors! Damage can occur if this test is done on other transistors (like TIP107 or TIP36).

      • Game is on, and the "test mode" button is pressed once. On 1993 and newer WPC games, coin door is closed.
      • Remove the backglass.
      • Find the transistor that controls the coil in question (refer to the manual).
      • Attach an alligator clip to the grounding strap in the bottom of the backbox.
      • Momentarily touch the other lead of the alligator clip to the metal tab on any TIP102 transistor (only works on these).
      • The coil should fire.
      • If the coil does not fire, and the coil did fire in the previous test, there probably is a wiring problem. A broken wire or bad connection at the connector would be most common. It is also possible there is a bad transistor. Use the DMM meter and test the transistor on the board (see Transistors Testing Procedures for details).

      The Above Tests Worked, but the Coil Still doesn't Work.
      If all the above tests worked, there is probably a driver board problem. Everything has been tested from the TIP102 back to the coil itself. That only leaves the TIP102 itself, its pre-driver transistor, and the logic chip that controls the transistors. It has to be one (or more!) of these devices that are causing the problem.

      Installing a New Transistor.
      If it has been determined a coil's driver board transistor is bad, there are a few things to keep in mind. Most TIP102 transistors also have a "pre-driver" transistor (2N5401 for WPC-S and prior, or MPSD52 for WPC-95). Both 2N5401 and MPSD52 transistors are basically the same (use either). They both cross to NTE288.

      If a coil's TIP102 transistor is replaced, it's a good idea to also replace its corresponding pre-driver. It will be located near the TIP102 transistor. See the schematics or the internal solenoid test "help" to determine the specific pre-driver transistor(s).

      Heavier duty coils use a bigger TIP36c driver transistor. These transistors have TWO pre-drivers: a TIP102 and a 2N5401 (or MPSD52) transistor. Again, if the TIP36c has failed, it's a good idea to replace both corresponding pre-driver transistors.

      Replacing the pre-driver transistors is optional (if they test Ok). Test these pre-drivers instead of just replacing them. But if the driver transistor has failed, the pre-driver was probably over-stressed too. It is a good idea to replace the pre-driver transistor(s) too.

      Don't Forget the 74LS374 TTL Chip!
      If a coil locked on really hard and for a period of time (and without blowing the coil fuse, over fused?), the controlling 74LS374 chip may have also died. If after replacing the TIP driver transistor(s) and the smaller pre-driver transistor, the coil is still locked on, now is the time to replace the 74LS374 TTL chip. Use the schematics and trace the transistors in question back to the 74LS374 chip. This will be chip U2, U3, U4, or U5 on WPC-S and prior driver boards, or chip U4, U5, U6, or U7 on WPC-95 driver boards.

      WPC Coil Diodes.
      On all electronic pinball games, each and every CPU controlled coil must have a coil diode. This diode is VERY important. When a coil is energized, it produces a magnetic field. As the coil's magnetic field collapses (when the power shuts off to the coil), a surge of power as much as twice the energizing voltage spikes backwards through the coil. The coil diode prevents this surge from going back to the driver board and damaging components.

      If the coil diode is bad or missing, it can cause several problems. If the diode is shorted on, coil fuse(s) will blow. If the diode is open or missing, strange game play will result (because the driver board is trying to absorb the return voltage from the coil's magnetic field collapsing). At worse a missing or open diode can cause the driver transistor or other components to fail.

      On non-WPC games, sometimes a diode lead breaks on the coil from vibration. Also, when replacing a coil, the operator can install the coil wires incorrectly (the power wire should always be attached to the coil's lug with the banded side of the diode). To prevent this, Williams moved the coil diode to the Driver board. This isolates the coil diode from vibration and eliminates the possibility of installing the coil's wires in reverse. This was done on all coils except the flipper coils.

    The coil diodes on a Fliptronics flipper coil. The red (bottom)
    wire is the "hot" wire. The yellow (middle) wire handles the initial
    hi-power "flip", and the orange (top) wire handles the flipper's "hold".

    fliptronics flipper coil and diodes

      Flipper Wire Colors.
      From game to game, Williams often used a consistent set of wire colors for flipper wiring (unfortunately, this is not always the case, as seen in the picture above). In the picture below, the flipper coil lugs are labeled "lug1" to "lug3". Here are the wire color break down for most games:

        Lug 1 (outside banded diode lug, two winding wires, 50 volts):
        • Lower Left flipper: Grey/Yellow
        • Lower Right flipper: Blue/Yellow
        • Upper Left flipper: Grey/Yellow
        • Uppper Right flipper: Blue/Yellow

        Lug 3 (outside non-banded diode lug, one winding wire):

        • Lower Left flipper: Orange/Blue
        • Lower Right flipper: Orange/Green
        • Upper Left flipper: Orange/Grey
        • Uppper Right flipper: Orange/Purple

        Lug 2 (middle lug):

        • Lower Left flipper: Blue/Grey
        • Lower Right flipper: Blue/Purple
        • Upper Left flipper: Black/Blue
        • Uppper Right flipper: Black/Yellow

    Flipper coil wiring. Note the wire color rules
    specified below are the "usual" wire colors (but can't
    be 100% guarenteed).

    The coil diodes on a Non-fliptronics flipper coil. Note the
    solo center wire and the all blue wire on the top lug goes to the
    EOS switch and the 2.2 mfd 250 volt spark arresting capacitor (the
    EOS switch and capacitor are wired in parallel). The blue/yellow
    (lower) wire (or gray/yellow) is the "hot" wire. The blue/violet
    (upper) wire continues to the cabinet switch, the driver board relay,
    and ultimately ground.

    non-fliptronics flipper coils and diodes

      Even on WPC games, the coil diode can fail. The coil diode can be tested. It is mounted on the driver board, near it's corresponding driver transistor (refer to the schematics; it's the diode that is tied to one of the legs of the driver transistor).

      Use a DMM set to "diode" setting, and test the board mounted coil diode. With the black lead on the banded side of the diode and the red lead on the non-banded side, a reading of .4 and .6 volts should be seen. Reverse the leads (red lead to banded side of diode), and a null reading should be seen. If this reading is not indicated, cut one lead of the diode from the driver board, and repeat the test. If these results are still not seen, replace the diode with a new 1N4004 diode.

      Installing a New Coil.
      Many replacement coils will come with a diode soldered across its solder lugs. On WPC games, all coils except the flipper coils have the diode mounted on the Driver board. For all coils except flipper coils, cut the diode off the coil before installing. Then solder the coil wires to either coil lug. The diode can also be left in place, but the coil wires must be installed correctly. The green (ground) wire MUST go to the lug of the coil with the non-banded side of the diode. The power wire solders to the lug with the banded side of the diode. If the wires are reversed, this essentially causes a shorted diode. Though the Driver board mounted diode is still present as protection, damage can occur to the coil's driver board transistor.

      Coil Doesn't Work Check List.
      If a coil doesn't work in a game, here's a check list to help determine the problem.

      Before starting, is the coil stuck on? (Hint: is there heat, smoke and a bad smell?). If so, the coil's driving transistor has probably failed. Turn the game off and check the driving transistor, and replace if needed. See Transistors Testing Procedures for more info.

      If the coil just doesn't work, here's a list of things to check:

      • Have the power wires fallen off the coil's solder lugs?
      • Is the coil damaged? Has the internal winding broken off the coil's solder lug?
      • Is there power at the coil? See Testing for Power at the Coil for more details.
      • If there is no power at the coil, check its fuse. Use the internal diagnostics and the "help" button to determine which fuse controls the coil. See Testing Transistors/Coils using the Diagnostics for details.
      • Check the other coils that share one of the same wire colors. Are they working too? If not, suspect the fuse that handles these coils.
      • Power to coils are often ganged together. If the power wire for this coil has fallen off a previous coil in the link, power may not get to this coil.
      • Using the DMM and its continuity test, make sure the coil connects to the correct connector/pins on the driver board. This information can be seen from the Diagnostics solenoid test.
      • Check the driving transistor. Usually this transistor will short on when it fails, but not always.


    3d. When things don't work: Game Resets (Bridge Rectifiers and Diodes)
      Game resets are probably the biggest problem with WPC to WPC-S games (and to a lesser extent, WPC-95 games). The pinball will seemingly shut off, then power back on (like the game was turned off and back on quickly). Typically, this will happen during game play, when the flippers are used. If the +5 volts (which powers all the logic circuits) dips momentarily below 5 volts (from heavy voltage draw when the 50 volt flippers are used), the "watchdog" circuit shuts the game down. The high current draw flippers stresses the other power components in the system. If these power components are starting to fail, the +5 volts dips, and the watchdog circuit resets the game. When the game shuts down, the power components under stress are relieved. Then the voltage returns to +5 volts, and the game powers back up. This reset process can happen anytime, but usually happens during game play.

      Check the Easy Stuff First.

      Proper AC Wall Voltage?
      Important: Before starting to dig in and try to diagnose the bridge rectifiers, set the DMM to AC Voltage and test the wall socket voltage. Make sure there is 110 to 120 volts AC present! If there is only 100 volts, this can cause the game to reset. If in Europe, and the game is set to 240 volts AC and yet there is only 210 volts at the wall plug, this can also cause the game to reset too. This problem happens mostly in the summer, when household power consumption is at a high, or if the game is plugged into the same circuit as another high power device. WPC pinball games draw a maximum of 8 amps of power. Most home circuits are 15 amps, so two pinballs on one circuit should be the maximum. Don't have the game plugged into the same circuit as another power sucking device (like an air conditioner, refrigerator, etc.).

      Re-seat the Transformer connectors.
      Though this doesn't tend to be a big problem, try re-seating the connectors on the large transformer in the bottom of the cabinet. Unplugging then plugging these connectors effectively cleans them and makes sure they are snuggly attached. If there is any resistance in the transformer plugs, that can reduce the voltages going to the rest of the game. This only takes a moment to do, so it's not a bad thing to try.

      Flipper Coil Diodes.
      Though not a big problem on WPC games, if the flipper coil diodes (there are two per coil) are damaged or missing, this too can cause game resets. This is a lot more common on games prior to WPC, but it can happen here too, and the diodes are needed. If missing or broken, resets can happen on and WPC or WPC-95 game.

      Failing Bridge Rectifiers, WPC-95 Diodes and Filter Caps.

      Bridge rectifiers or diodes (and their corresponding filter capacitor) convert AC voltage to smooth DC voltage. This is very important, as all the circuit boards run on DC voltage. If a game plays fine, but randomly resets, often the bridge rectifiers (or diodes) and their capacitor are over stressed and need replacement. On WPC-S and prior games, a bad bridge rectifier is probably the single most commonly failed component relating to game resets.

      A bad bridge rectifier (or diodes on WPC-95), or cracked solder pads around a bridge can also give game boot-up error messages saying fuse F114/F115 (or F106/F101 on WPC-95) have failed, when the fuses are actually good. See the Check the Fuses section (and below) for a list of fuses and what bridges they connect to.

      WPC bridge rectifiers and diodes reside on the driver board (although there is also a bridge on the Fliptronics board prior to WPC-95). A bridge rectifier is mearly four diodes strung together in a square. There are two AC input voltages, and two DC (positive and negative) output voltages. These diodes are encased in epoxy, and covered with a square metal casing.

      Failed bridges/diodes can often short or "go open". BOTH of these problems are quite common! A shorted bridge/diode will immediately blow a fuse when powered on. An open bridge/diode will cause lower or no voltage to get past the bridge. If the fuses are good, but power driver board LEDs are not lit, this could be an indicator of a bridge/diode that has "gone open".

    Bridge rectifiers on a WPC-S and earlier generation
    driver boards. From the left to right: BR3, BR4, BR2 (top),
    BR1 (bottom). BR2 and BR1 have a large silver heat sink
    over them.

    The BR5 bridge used on WPC-S and earlier generation
    driver boards. Note the "+" lead of the bridge is offset
    slightly, from an otherwise perfect square shape. Notice
    the bridge is installed about 1/4" above the board.
    This aids air flow and keeps the bridge cool.

      WPC-95 "Bridges".
      When WPC-95 was released, Williams decided to stop using bridge rectifiers. Instead they just installed four diodes right on the driver board for each replaced bridge. By using four discrete diodes instead of a single bridge, the heat generated by the components is spread out and reliability is greatly improved. Bridge rectifier failure is very common in WPC-S and prior systems. Replacement of even a single diode in the WPC-95 system games is very rare (but these games are not as old as WPC-S and prior systems). Certainly all the problems associated with the bridge rectifiers can still be exhibited in a WPC-95 system too.

      The diodes used in WPC-95 are called P600D (or 6A4 or 6A400). These are 6 amp at 400 volt rectifiers. A substitute device is NTE5814.

    WPC-95 P600D diodes D7 to D22 which replaced MB3502W/MB352W bridge
    rectifiers. Also note the smaller "T" fuses (on the right) used in WPC-95.

    WPC-95 diodes

      The Electrolytic Capacitor: the Bridge Rectifier and Diode's Partner.
      Each bridge rectifier or diode set must also have an associated electrolytic capacitor. These are needed to polish the converted rough DC voltage to smooth DC voltage.

      Electrolytic caps are largely mechanical devices. With time, they can fail. Expect about 10 years maximum life from an electrolytic filter capacitor. It is fairly common for these caps to fail. A failing electrolytic capacitor can cause the game to reset, as the DC voltage won't be "smooth". Because of this, when replacing the BR2 bridge on pre-WPC95 games, it is a good idea to also replace the associated filter capacitor C5 (15,000 mfd 25 volts).

      Smaller Filter Caps Used with WPC-95. Why?
      Interestingly, Williams changed from 15,000 mfd (at C5) on WPC-S and prior, to a lower value of 10,000 mfd on WPC-95 (at C9). With time, WPC-95 games may be more sensitive to bad filter caps, because of this lower value. Right now, since these games are fairly new (1996 and later), this isn't a huge problem.

      Higher filter cap values are generally good; they provide a better level of AC filtering as the capacitor gets older. As electrolytic capacitors wear (they really are a mechanical device), they are less efficient at AC filtering, and their MFD value drops. However, the higher the MFD value of a capacitor, the more strain it puts on the rectifying bridge or diodes. When a game is turned on, the filter cap draws significant current during the first half AC cycle (since this power is used to "charge" the capacitor). This can subject the bridge rectifier (or diodes) to an excessive in-rush of current. This in-rush current can be up to ten times the current needed after the filtering capacitor has charged. This can cause a connection inside a bridge to instantly go open (this is not the same as over-current, which can cause the bridge to short). In-rush current is a factor of both voltage and the capacitor. A larger cap will force more in-rush current to the bridge, potentially causing damage. Also capacitors with higher MFD values cost more (the change from 15,000 to 10,000 mfd could have been in fact a cost/availability issue; the 10,000 mfd capacitors may have had a shorter lead time, and were cheaper for Williams to buy).

      Bridge Rectifier, Diode, and Filter Capacitor Device List.
      Here's a list of what bridge rectifiers and diodes control which functions, and their associated capacitors. All are located on the driver board, unless otherwise stated.

        WPC-S and Earlier Driver Board:
        • BR1 to C6 & C7 (15,000 mfd @ 25v) to F114: +18 volts used for lamp driver columns. Then the 18 volts goes through voltage regulator Q2 (LM7812) and F115, and is converted to 12 volts (regulated) for the switch matrix.
        • BR2 to C5 (15,000 mfd @ 25v) to F113: +5 volts. The bridge and cap that fail the most.
        • BR3 to C8 (100 mfd @ 100v) to F112: +50 volts, used for solenoids.
        • BR4 to C11 (15,000 mfd @ 25v) to F111: +20 volts, used for flash lamps.
        • BR5 to C30 (15,000 mfd @ 25v) to F116: +12 volts unregulated for playfield devices, dot matrix display, and the coin door.
        • BR1 (on Fliptronics II board) to C2 (100 mfd @ 100v) to F901-F904: +50 volts used for the flippers. Located on the Fliptronics II board.

        WPC-95 Driver Board:

        • D3, D4, D5, D6 to C8 (10,000 mfd @ 35v) to F109: +12 volts unregulated for playfield devices, dot matrix display, and the coin door.
        • D7, D8, D9, D10 to C9 (10,000 mfd @ 35v) to F105: +5 volts for all board logic circuits. The diodes and cap that fail the most.
        • D11, D12, D13, D14 to C12 (10,000 mfd @ 35v) to F106/F101: +18 volts used for lamp driver columns. Then the 18 volts goes through voltage regulator Q2 (LM7812) and F101, and is converted to 12 volts (regulated) for the switch matrix.
        • D15, D16, D17, D18 to C10 (10,000 mfd @ 35v) to F109: +20 volts for flash lamps.
        • D19, D20, D21, D22 to C22 (100 mfd @ 100v) to F102/F103/F104: +50 volts for solenoids.
        • D25 to D32: +6.3 volts for general illumination. These were replaced with jumpers starting with Scared Stiff. See the Burnt Connector section (WPC-95 GI diodes D25-D32 remove and jumper) for a description of this.

      Testing a Bridge (WPC-S and prior), Board Removed.
      Note testing a bridge with the game off is NOT conclusive to whether the bridge is bad! The bridge is being tested under NO load. Only a bridge which is shorted (and hence is blowing fuses) or open will test as "bad". A bridge could test as "good", and still cause the game to reset. Also testing a bridge "in circuit" (while still soldered in the board) can often not give proper results.

      A bridge has four terminals: two AC terminals, and two DC terminals (postive and negative). On the side of each bridge, printed on the metal casing, there will be two labels: "AC" and "+". From the solder side of the driver board, mark with a Sharpie pen these two terminals. Figuring out the other two terminals is easy: the other AC terminal is diagonal to the labeled AC lead. The negative DC lead is diagonal to the labeled positive DC lead. Mark these right on the board with the Sharpie pen. To double check, the two DC leads (positive and negative) connect to that bridge's respective electrolytic capacitor, and it's positive and negative leads. Testing a bridge while soldered in the board (in curcuit) may not give the following results. For example, testing BR2 in curcuit will not give these results (but most of the other bridges will). To test the bridge:

      1. Put the DMM on diode setting.
      2. Put the red lead of the DMM on one of the AC terminals.
      3. Put the black lead of the DMM on the positive DC lead. A reading of between .4 and .6 volts should be indicated.
      4. Put the red lead of the DMM on the other AC terminal. Repeat step #3.
      5. Put the black lead of the DMM on one of the AC terminals.
      6. Put the red lead of the DMM on the negative DC lead. A reading between .4 and .6 volts should be indicated.
      7. Put the black lead of the DMM on the other AC terminal. Repeat step #6.

      If values outside of .4 to .6 volts are shown for any of the above tests, the bridge is bad. Typically you will get a zero value (a short) for at least one of the above tests in a bad bridge.

      Testing a Bridge (WPC-S and prior), Under Load, In the Game.
      This tip is from John Robertson. This test is a more conclusive way to test a bridge. This procedure requires a DMM, two alligator jumper wires, and a 6 amp rectifying diode (6A50 or 6A2 or 6A4, or whatever is available; Radio Shack sells 6A50 diodes, part number 276-1661). Here is the procedure:

      1. With the game off, clip one end of an alligator test wire on the "+" lead of bridge BR2 (top most bridge) on the driver board. The "+" lead is the top left most lead (see picture below). Often the side of the bridge is labeled too. One lead is "AC", and the other is "+" (connect the alligator clip to the "+" lead, which is the left lead as facing the board).
      2. Connect the other end of the alligator test wire on the RED lead of the DMM.
      3. Put the BLACK lead of the DMM on the braided metal grounding strap at the bottom of the backbox.
      4. Turn the DMM on, and set it to DC Volts (20 volt range).
      5. Turn the game on. A value of 12 to 13 volts should be shown. Any less than 12 volts, and the bridge (or the connection to the bridge) is bad.

    Attaching the red alligator test lead to the "+" leg of bridge BR2.
    The other end of the alligator lead is attached to the DMM's red
    probe.

      1. Turn the game off. Take the second alligator jumper wire, and connect the clip to the BANDED end of the 6 amp diode.
      2. Connect the other loose end of the alligator jumper wire to where the first alligator clip connects to the red lead of the DMM (see picture below). This is essentially the same as connecting the second alligator clip to the "+" lead of bridge BR2 (but there is not enough room at the bridge to do this, since the first alligator clip is in the way).
      3. Turn the game on.
      4. Touch the non-banded end of the diode to connector J101 in either pin 1 or 2 (two top most pins). Note the IDC connector will have some exposed metal at the top of the connector to touch, and plug should not be removed.
      5. While doing the above step, examine the DMM voltage reading. If the voltage rises when the diode lead is touched to Connector J101 pin 1 or 2, the bridge BR2 is bad (bad internal positive diode).

    A second alligator clip is connected to where the first alligator
    clip connects to the red lead of the DMM. Now touch the
    second alligator clip with a 6 amp diode, NON-BANDED end, to
    connector J101 pins 1 or 2. The voltage on the DMM should
    NOT drop when the diode is touched to connector J101 pins 1 or 2.

      1. Turn the game off. Reverse the diode in the alligator clip so the NON-BANDED end of the 6 amp diode is connected to the alligator clip.
      2. Connect the other end of the alligator clip to TP5 (ground).
      3. Turn the game on.
      4. Touch the banded end of the diode to connector J101 in either pin 1 or 2 (two top most pins). Note the IDC connector will have some exposed metal at the top of the connector to touch, and the plug should not be removed.
      5. While doing the above step, examine the DMM voltage reading. If the voltage rises when the diode lead is touched to Connector J101 pin 1 or 2, the bridge BR2 is bad.

      If the above tests all work as described (no voltage drops or readings below 12 volts), the problem is mostly likely a bad C5 (15,000 mfd 25 volt) filter cap (or a cracked solder joint to the bridge and/or capacitor, which can be solved by installing the jumper wires described below).

    The second alligator clip is now connected to TP5 (ground), and
    the diode is reversed in the alligator clip. Touch the other end
    of the second alligator clip with the 6 amp diode, BANDED end, to
    connector J101 pins 1 or 2. The voltage should not drop when the
    diode is touched to connector J101 pins 1 or 2.

      Testing a Diode (WPC-95)
      The diodes that replaced the bridge rectifiers in WPC-95 are even easier to test. Again, testing diodes in curcuit may not give the following results.

      Also, testing a diode is NOT conclusive to whether the dioide is bad! The diode is being tested under NO load. Only a diode which is shorted (and hence is blowing fuses) will test as "bad". A diode could test as "good", and still cause the game to reset.

      1. Put the DMM on diode setting.
      2. Put the black lead of the DMM on the banded lead of the diode.
      3. Put the red lead of the DMM on the non-banded lead of the diode.
      4. A reading between .4 and .6 volts should be indicated.

      The Above Bridge/Diode Tests Don't Always Work!
      Yes, you heard right. The above outlined bridge and diode tests above don't always find a faulty component. These devices can just start to fail, and this will cause the game to reset. But a bridge or diode can become "leaky", which will cause the game to reset, and may not show as bad in the above tests (though the bridge test "under load" as explained above is the most accurate of the tests).

      So what do you do now? How can you be sure the resetting game has a bad bridge or diode? Well you really can't! First make sure the wall voltage is at the proper level. Then re-solder the bridge/diodes and their associated capacitor's solder pads. Then just go ahead and replace the suspected bad bridge/diode (BR2 or D7, D8, D9, D10 on WPC-95). If the game is still resetting, replace the associated filter capacitor (C5 or C9 on WPC-95). If the game is still resetting, replace the LM339 voltage comparitor at U6 (U1 on WPC-95) as a last resort.

      Replacing a Bridge or Diode.
      Replacement is as simple as cutting out the old component and soldering in a new one. When installing the new bridge, mount it 1/4" or even 1/2" above the board. This allows for air to flow underneath the bridge for better cooling.

      Replacing BR1 and/or BR2 on WPC-S and Prior.
      When replacing either (or both) bridges BR1 and BR2 on WPC-S and prior, both bridges will have to be dealt with. These two bridges share a single large silver heat sink. Since they both share the same heat sink (and one failed due to heat), the other probably will need replacement shortly. If either BR1 or BR2 is bad, replace them both. To remove them, both will need to be unsoldered from the Driver board, and the heat sink un-screwed from the bottom of each bridge. The new bridge is then screwed to the heat sink, and both bridges re-installed. There should be some white heat sink compound on the top of the bridges too. Make sure to add some heat sink compound when replacing the bridges. Heat sink compound can be purchased at Radio Shack.

      Replacement Bridges and Diodes.
      The stock bridge installed in WPC games is 35 amps at 200 volts. The original part number will be something like "MB3502W" or "MB352W". The "MB" signifies a metal cased bridge. The "35" signifies 35 amps. The "02" or "2" signifies 200 volts peak. The "W" at the end means the bridge has wire leads. Higher amps or voltage ratings work fine. I generally use 35 amps at 400 volts for example.

      Replacement wire lead bridges are available from Competive Products Corp (800-562-7283), or from Williams, part number 5100-09690. Mouser also sells them, part number 625-GBPC3502W ($3.48). And so does Digikey, part number MB352WMS-ND. Radio Shack even sells 35 amp bridges at 50 volts (which isn't enough voltage). But look at the bridge inside the Radio Shack package, as often they are labeled 3502W or 352W (35 amps 200 volts), and not 50 volts. Always buy only the labeled bridges from Radio Shack. Sometimes these "35 amp" bridges are labeled 1001W (10 amp 100 volts!). Obviously put that one back and grab another!

      Replacement diodes for WPC-95 boards are P600D (6A4 or 6A400), or NTE5814. A lower voltage version can be used too, 6A2 or 6A200 (200 volts). Radio Shack sells a 6 amp 50 volt (6A50) version which can be used in a pinch, part number 276-1661.

      Testing the Filter Caps.
      Testing the filter capacitors on the driver board is fairly easy. With the game on, set the DMM to AC volts. Then put the leads of the DMM across the two leads of each filter capacitor (doesn't matter which DMM lead to which capacitor lead, as AC voltage is being measured). If more than 0.30 volts AC is seen, the capacitor is bad.

      The problem with this test is the leads for the filter caps are nearly impossible to access, when the board is installed in the game! For this reason, I usually just replace the filter cap in question (C5 or C9 on WPC95) when in doubt.

      Replacement Filter Caps.
      If replacing a filter capacitor, use a 15,000 mfd 25 volt "snap" cap (on any WPC generation, even WPC-95). Higher voltage caps can be used (but are more expensive). Do not use a capacitor greater than 15,000 mfd, because the in-rush current puts more stress on the rectifying bridge/diodes. A lower value of 10,000 or 12,000 mfd could also be used (but no lower than 10,000 mfd). These are available from many sources, such as Digikey (www.digikey.com or 800-344-4539) or Mouser (www.mouser.com or 800-346-6873):

      • 15,000 mfd 25 volt, Mouser part# 5985-25V15000 $4.63 each, or Digikey part# P6577-ND $5.52 each.
      • 12,000 mfd 25 volt, Mouser part# 5985-25V12000 $4.95 each, or Digikey part# P6575-ND $4.74 each.
      • 10,000 mfd 25 volt, Mouser part# 5985-25V10000 $3.65 each, or Digikey part# P6573-ND $4.17 each.

      Reflowing Bridge or Diode Solder Joints.
      Often a bridge or diode will test Ok, but the game still resets. This can be caused by cold, fatigued, or cracked solder joints on a bridge. Since bridges (especially BR2) and diodes can get hot, they will mildly heat up a solder joint, and make it go "cold" or fatigued. Reflowing these solder joints with new solder often fixes this problem. Also reflow the solder joints on the bridge or diode's associated filter capacitor. Often these solder joints crack.

      The problem with reflowing the solder joints on the bridges and capacitors is this; often the traces on the top side of the board (which can not be accessed because of the components), do not get as good solder contact. This can cause an intermittent connection, which can lead to game resets. The best solution to this problem is adding some jumper wires (see below).

      Insurance: Installing Bridge/Capacitor Jumpers.
      Another problem with the bridge rectifiers/diodes and the filter capacitors are their solder pads. The WPC driver board is a double sided board (that is, it has "traces" running on both sides of the board, both leading to different components). Soldering of both top and bottom traces is done on the bottom (solder side) of the board. Since the components themselves are in the way on the top side of the board, it is hard to even see the component side solder pads.

      The problem is this; these components (bridges/capacitors) are large, and they can get hot (softening the solder). Vibration, heat, or both, can cause the solder points to crack. This can cause an intermittent connection. This can cause game resets, or whole banks of coils or lamps to not work.

      Reflowing the solder on the back of the driver board is one solution. But it really isn't the ultimate solution. Since the driver board is a double sided board, and the components on the top side of the board are large, the traces can only be soldered on the bottom side of the board. This does not guarentee a good connection to the traces on the top (component) side of the board. To fix this problem, it is recommended to add jumper wires on the solder side of the driver board. This is done to back up the bridge/capacitors' component side board traces.

      The most important bridge/capacitor to jumper is BR2 and C5. Jumper two 18 guage wires on the solder side of the driver board from BR2 to C5 (positive lead of BR2 to positive lead of C5, and negative lead of BR2 to negatvie lead of C5). This will help prevent random game resets. All the other bridges/capacitors can be jumpered too.

      Installing the Jumpers.
      When installing the jumpers, first label the back of the driver board. Use a "sharpie" pen and label the bridge, and its "+" and "-" leads, on the back side of the driver board. The positive lead of the bridge is the one offset lead in the square. The negative lead is diagonal the postive lead. The other two diagonal legs are the AC leads. Also label the capacitor and it's positive lead with a sharpie pen (the positive lead on most of the filter caps is the "top" lead). Double check all potential connections with a DMM, and buzz out the jumper paths BEFORE you install them (installing a jumper incorrectly can cause SERIOUS problems!). This will make installing the jumpers much easier and error-free.

      Here is a list of jumper wires that should be added to WPC and WPC-S driver boards. For reference, the driver board is positioned with the solder side showing, and connector J104 at the "top":

      • BR2 to C5: two jumpers. Jumper the positive lead of bridge BR2 to the positive lead of C5. Repeat for the negative leads also.
      • BR1: ONE jumper. Jumper the AC lead of BR1 (just below the positive lead) to connector J101 pin 7.
      • C6/C7: jumper the two positive leads of capacitors C6 and C7 together (this also jumpers also helps BR1).
      • BR3: three jumpers. Jumper the lower AC lead of BR3 (just below the positive lead) to connector J104 pin 1. Jumper the other upper AC lead (to the left of the positive lead) to connector J104 pin 2. Jumper the positive lead of BR3 to the large solenoid fuse trace about 2" below the bridge (see picture below).
      • BR4: three jumpers: Jumper the negative lead of BR4 to the negative lead of C11. Jumper the AC lead of BR4 (just above the negative lead) to connector J102 pin 1. Jumper the other lower AC lead of BR4 (just below the positive lead) to connector J104 pin 4.
      • BR5 to C30: two jumpers: Jumper the positive lead of BR5 to the positive lead of C30. Repeat for the negative leads also.

All the above jumpers have been installed. The most important jumper
is the one from BR2 to C5 (the gray wires). Note the "+" (offset leg)
of the bridge goes to the "+" lead of the associated capacitor. The
"-" lead of the bridge is diagonal to the offset "+" lead. Shown is a
WPC and WPC-S style driver board.

    Probably the second most important jumpers
    to install are those from BR5 to C30.
    Note the "+" (offset leg) of the bridge
    goes to the "+" lead of the associated
    capacitor. The "-" lead of the bridge is diagonal
    to the offset "+" lead. Shown is a WPC and WPC-S
    style driver board.

      Are Jumper Wires Good Insurance for WPC-95 Games Too?
      Yes! Even though WPC-95 games stopped using bridges in favor of diodes (which have far less heat/vibration solder pad cracking problems), jumper wires are still a good idea. On WPC-95 games, all the large electrolytic capacitors on the driver board have the potential for cracked solder pads.

      To give an example of solder pad cracking, I recently had a problem on a Safe Cracker (WPC-95) where none of the low power (20 volt) coils worked. It was very frustrating; the fuse was good, and power was getting to the Driver board, but not out of the driver board and to the coils.

      It turned out that the capacitor that filters the DC voltage after the bridge rectifier on the Driver board had a cracked solder pad. This prevented the voltage from getting any further than it's associated bridge rectifier (I should have known; the +20 volt LED on the Driver board was not lit!). Adding the jumper wires from the bridge to the capacitor fixed the problem.

      Replace the Filter Capacitor at C5 (or C9 on WPC-95).
      If the game is still resetting, there's probably a good chance that the filter capacitor at C5 (15,000 mfd @ 25v) or C9 (WPC-95, 10,000 mfd @ 25v) needs to be replaced. The C5/C9 capacitor filters and smooths the +5 volts. If this cap is worn out, unsmooth +5 volts will result. This will cause random game resets. On WPC-S and prior games, when replacing bridge BR2, it is a good idea to just go ahead and replace the filter cap C5 with a new 15,000 mfd 25 volt capacitor.

      Check the Power Driver Voltage Plugs.
      The molex plug that provides the input voltage to the driver board can also have problems. On WPC-95, J129 supplies the voltage that gets rectified to +5 volts. On WPC-S and prior, J101 handles this. Also check the main power plugs that supply +5 and +12 volts to the power driver boards. On WPC-S and prior, this is J114. On WPC-95, this is J101.

      Make sure the above connectors are in good condition. Check the pins on the driver board for burnt pins, cold/fatiqued or cracked solder joints (also see the Burnt Connector section). Any problems with the above mentioned connectors can cause random game resets.

      Game is Still Resetting.
      As a last thing to check, the LM339 voltage comparator at U6 (U1 on WPC-95) on the power driver board could be bad. This chip is in the zero crossing circuit. If bad or leaky, this will cause game resets too. Replace the LM339, and make sure to install a socket for this chip.

      Yet another reset problem can be caused by the CPU board chips at U1, U2, U3 and U5 (all WPC revisions). These chips connect directly to the CPU, and can have heat problems that cause a game to reset.

      Last Reset Resorts - Failing Dot Matrix Controller/Display.
      The game in question was Star Trek Next Generation, and the symptoms included occasional game resets, weak flippers, and dim lights. The usual stuff was tried: replaced all the bridge rectifers and filter caps, rebuilt the flippers, etc, and nothing worked. A bad transformer was suspected, so it was re-taped for 100 volts, as an experiment. After powering the game back on, immediate smoke was seen off the dot matrix display controller board. On closer inspection, a number of the diodes and large resistors on the dot matrix display board showed signs of severe heating (the experiment with the lower voltage tap wasn't nearly long enough to cause the damage observed - this had built up over considerable time). After rejumpering the game back to 115 volts, a spare dot matrix display board was installed in the game, and everything worked: bright lights, strong flippers, and no game resets.

      In this case the high-voltage supply circuits on the dot matrix display controller board were marginal. A considerable amount of current was being drawn by the dot matrix display board. This problem caused enough load on the transformer to bring all the voltages down for the whole game (there was a clue: with the game turned on, the AC inputs into the bridge rectifers all read at the low end of the acceptable range).

      Even having an "out-gassed" dot matrix display with a good dot matrix controller board can cause game resets (see Dot Matrix/AlphaNumeric Score Displays for more details on out-gassing displays). The problem of weak, old, out-gassed dot matrix displays causing game resets is becoming more common. The moral of this story is to not use a dot matrix display that is out-gassed and at the end of its life.

      Lesson: not all game resets and low voltage problems are caused by the notorious bridge rectifers. Bad CPU chips or bad voltage supply circuits on the dot matrix display board can also mimic these problems. Check the large resistors and diodes near the heat-sunk transistors on the dot matrix controller board. Look for clear signs of overheating (blackened PC board), even though the board is functional. To fix this, rebuild the high voltage section of the dot matrix display board, as described later in this document in the Dot Matrix/AlphaNumeric Score Displays section. Also be sure to replace a marginal dot matrix display. A bad display can consume much more power, stressing the dot matrix controller board, and potentially lowering other voltages, and causing game resets.

      The Thermistor and Resets.
      The Thermistor's job is to act like a low value resistor when cold. After warming up for a minute, it essentially becomes a zero ohm resistor. When the game is first turned on, it provides a slightly lower input voltage to the game's transformer (and hence bridge rectifiers), limiting the in-rush current (and lengthening the life of the bridges). But with time, sometimes the thermistor does not function correctly after warm up, therefore acting like a full time resistor. This keeps the input voltages lower, and makes game resets more prevalent. The Thermistor is located in the "power box" just inside the coin door. This power box also housing the game's power switch.

      With the game turned on and warmed up (five minutes), no more than 1.00 volts AC should be seen across the Thermistor, with the game in the attract mode (not playing). Please be careful as there is 115VAC (or 220VAC for Europe) in this box and can be dangerous.

    The "power box" just inside the coin door.
    Picture by John Robertson.

    Measuring the AC voltage across the Thermistor, with the game in
    attract mode. No more than 1.00 volts AC should be seen.
    Picture by John Robertson.

      Fuse F116 Keeps Blowing on WPC-S and Prior Games.
      When fuse F116 keeps blowing on WPC-S and earlier games, it's almost always a bad bridge rectifier at BR5. Replace and make sure there is good solder contacts leading to the "+" lead of C30.

      "Check Fuse F114/F115" (or F106/F101) Message.
      This indicates the voltage is out for the lamp/switch matrix. Sometimes this message is gotten even when the fuses are good!

      A failing bridge (or diodes) can cause the game to think their respective fuses are bad. If the fuse F114 (or F106 on WPC-95) is actually blown, usually this is an indication that BR1 (or diodes D11-D14 on WPC-95) usually failed. But it could be as simple as a cracked solder pad on power driver board's BR1 (or diodes D11-D14 on WPC-95). See the above about jumper wires, and install those for good reliability. The shotgun method can also be used, replacing BR1 (and BR2, both for WPC-S and prior, while you are at it!) on the power driver board, in addition to the jumper wires.

      Here is a step-by-step test to see exactly what is causing the F114/F115 (or F106/F101) error message. With the game on and the coin door closed:

      • Test for AC voltage at J101 pins 4 and 7 (or J129 pins 4 and 7 on WPC-95). A reading of 13 to 18 volts AC should be seen. This is the AC voltage coming from the transformer. If no voltage here, check the Molex connectors around the transformer and at the power driver board.
      • Test for DC voltage at TP8 (or TP102 on WPC-95) and ground. A reading of 16 to 18 volts DC should be seen. If no voltage here, replace BR1 (or D11 to D14 on WPC-95). Also no voltage here can occur because the solder pads are cracked around bridge BR1 (or D11 to D14 on WPC-95). Using jumper wires for BR1 (as described in the Game Resets section) helps prevent this.
      • Test for DC voltage at TP3 (or TP100 on WPC-95) and ground. A reading of 12 volts DC should be seen. If no voltage here, check or replace diodes D1 and D2 (1N4004, all WPC version).
      • If diodes D1/D2 are OK, replace Q2 (all WPC versions), a LM7812 voltage regulator.
      • If the above still does not fix the problem, replace U20 (all WPC versions) on the CPU board (ULN2803). If U20 died "hard", it could also blow the 74LS374 at U14 (on WPC-95 it's U23, a 74HC237) on the CPU board.
      • If the above still does not fix the problem, and the game has an under-the-playfield optic board, replace the LM339 chips on this board. Replace them all, and use sockets.
      • If voltage is still not right, or BR1 (or diodes D11 to D14 on WPC-95) are REALLY hot, check all the TIP107 transistors on the power driver board. If these test good, check/replace the power driver board's ULN2803 at U19 (or U11 on WPC-95), or maybe the power driver board's 74LS374 at U18 (or U10 on WPC-95).

      ALso on WPC-S and prior games, connectors J114, J116, J117, J118 can be removed. Replace the fuse and power on the game. If the fuse blows, its corresponding bridge rectifier is most likely shorted and should be replaced. If the fuse doesn't blow, the problem is not in the circuit boards. Most likely a shorted wire, which can only be manually hunted down.

      Burnt +18 Volt BR1 Bridge or WPC-95 Diodes D11-D14.
      This problem is strange, but a lot more common than one might think. The +18 volt (lamp columns) bridge or WPC-95 diodes get excessively hot and burns. I've seen this where the driver board is black from the heat. This happens because the lamp matrix is demanding more power than the circuit is designed to handle. Eventually the associated fuse F114 or F106 (WPC-95) will blow. Note the BR1 bridge or WPC-95 diodes D11-D14 are probably OK. If these were bad, the fuse F114 or F106 (WPC-95) would blow immediately.

      The reason for the burned bridge or diodes is simple; for some reason, one (or more!) of the lamp columns is stuck "on". Remember, the lamp matrix uses 12 volts, but this is derived by strobing (turning on and off very quickly) 18 volts. If a column locks on, instead of getting 12 volts, the full 18 volts is delivered. This added voltage puts stress on the lamp column circuit, and causes the +18 volt BR1 bridge or WPC-95 diodes D11 to D14 to get really hot (and their associated fuse to eventually blow).

      To fix this, first check all the TIP107 column driver transistors (see the Checking Transistors section). If none of these transistors are shorted on, then next suspect the ULN2803 at U19 (or U11 on WPC-95), or maybe the 74LS374 at U18 (or U10 on WPC-95). If the TIP107 transistors are OK, the ULN2803 is probably the culprit. An easy way to tell if the lamp matrix has a problem is to notice the controlled lamps right when the game is turned on. If any playfield lamps flash on right at power-on, there may be a problem with the ULN2803 driver chip.

      Exploding +20 volt Capacitor.
      There are cases when the +20 volt capacitor (Driver board C11 on WPC-S and prior, C10 on WPC-95) can just explode. This happens when a shorted flipper coil diode or shorted transistor on the Fliptronics board causes the 70 volt coil power to feedback into the 20 volt flashlamp circuitry. Because of reverse voltage, this blows the 20 volt capacitor. Also installing one of the ribbon cable connectors in the backbox on the header pins (top row of header pins to bottom row of housing) can do the same thing. And lastly, if connector J124 is mistakenly plugged into the driver board connector J128 (they are keyed alike!), this can cause capacitor C11 to explode.

      First check the ribbon cable header pins to make sure they are attached correctly. Then check the flippers. If when the flippers are activated, one of the flashlamps dimly lights, there may be a bad flipper transistor on the Fliptronics board.

      There is a preventive measure which can be taken for this. Install a blocking diode on the driver board ceramic 10 watt resistor R224 (or R9 on WPC-95). To do this, first remove the lower leg of resistor resistor R224 (the leg just above TP7). Connect the anode (non-banded end) of a 1N4004 (or 1N4007) diode to the resistor's leg. Then solder the cathode (banded side) of the diode back into the driver board (where one leg of R224 was removed). This will prevent the problem.


    3e. When things don't work: Problems with Flippers
      Flippers connect the player to the pinball game. Having perfectly working flippers is extremely important. Here are some common flipper problems and answers.

      Remember, all flippers (regardless of the game) will have EOS (end of stroke) switches. This tells the CPU a flipper is at full extension. If this switch is broken, it could cause problems (depending on the WPC generation). Bad EOS switches should always be fixed.

      How Flippers Work.
      Flipper coils are actually two coils in one package. The "high power" side is a few turns of thick gauge wire. This provides low resistance, and therefore high power. The "low power", high resistance side is many turns of much thinner wire. This side of the coil is important if the player holds the cabinet switch in, keeping the flipper coil energized. The high power low resistance side of the coil is only active when the flipper is at rest.

      To simplify how the two sides of a flipper coil work, it's best to examine the non-fliptronics version. In this case, when the flipper is energized and at full extension, the normally closed EOS switch opens. This removes the high powered side of the coil from the circuit. The low powered side of the flipper coil is always in the circuit, but is essentially ignored when the high powered side is in the circuit. This happens because the current takes the easiest path to ground (the low resistance, high power side of the coil). The low power high resistance side of the flipper coil won't get hot if the player holds the flipper button in.

    A simplified drawing of the flipper circuit in non-fliptronic games.

      EOS Switches: Normally Closed or Normally Open?
      Pre-fliptronics games have a high voltage, normally closed end-of-stroke (EOS) switch. But Fliptronics flippers are basically an electronic (instead of mechanical) version of the above explained non-fliptronics flippers. The main difference is fliptronics flippers have EOS switches that are low voltage, normally open switches (instead of high voltage, normally closed as used on non-fliptronics flippers).

      Is the problem Mechanical or Electrical?
      Before diving into any flipper problem, identify if the problem is mechanical or electrical. For example, if a flipper gets stuck in the "up" position during a game, is it a mechanical binding problem, or an electrical problem? In this case it's simple to tell; just turn the game off! If the stuck flipper falls back to rest, the problem is electrical. If the flipper stays in the up position, it's a mechanical problem. Knowing this will help fix flipper problems.

      Flipper Diodes.
      All WPC games will have diodes attached at the flipper coil. Make sure these diodes are oriented like the ones pictured below.

    The coil diodes on a Fliptronics flipper coil. The red (bottom) wire
    is the "hot" wire. The yellow (middle) wire handles the initial hi-power
    "flip", and the orange (top) wire handles the flipper's "hold".

    fliptronics flipper coil and diodes

      Flipper Wire Colors.
      From game to game, Williams often used a consistent set of wire colors for flipper wiring (unfortunately, this is not always the case, as seen in the picture above). In the picture below, the flipper coil lugs are labeled "lug1" to "lug3". Here are the wire color break down for most games:

        Lug 1 (outside banded diode lug, two winding wires, 50 volts):
        • Lower Left flipper: Grey/Yellow
        • Lower Right flipper: Blue/Yellow
        • Upper Left flipper: Grey/Yellow
        • Uppper Right flipper: Blue/Yellow

        Lug 3 (outside non-banded diode lug, one winding wire):

        • Lower Left flipper: Orange/Blue
        • Lower Right flipper: Orange/Green
        • Upper Left flipper: Orange/Grey
        • Uppper Right flipper: Orange/Purple

        Lug 2 (middle lug):

        • Lower Left flipper: Blue/Grey
        • Lower Right flipper: Blue/Purple
        • Upper Left flipper: Black/Blue
        • Uppper Right flipper: Black/Yellow

    Fliptronics flipper coil wiring. Note the wire color rules
    specified below are the "usual" wire colors (but can't be
    100% guarenteed).

    The coil diodes on a Non-fliptronics flipper coil. Note the
    solo center wire and the all blue wire on the top lug goes to the
    EOS switch and the 2.2 mfd 250 volt spark arresting capacitor (the
    EOS switch and capacitor are wired in parallel). The blue/yellow
    (lower) wire (or gray/yellow) is the "hot" wire. The blue/violet
    (upper) wire continues to the cabinet switch, the driver board relay,
    and ultimately ground.

    non-fliptronics flipper coils and diodes

      If the flipper(s) don't work at all...
        Non-Fliptronics Games:
        • Check the flipper fuses on the driver board, fuses F101 and F102.
        • On non-fliptronics games, clean the flipper cabinet switch contacts and the EOS switch contacts with a small metal file. Make sure this normally closed EOS switch is adjusted properly. The switch should open about 1/8" at the flipper's end of stroke. If this switch is dirty or not closed, the flippers may not work at all.
        • Check the DPDT flipper engage relay on the driver board. When this relay is energized, it completes the ground path for all the flippers. Transistor Q99 (2N5401) controls this relay (if this transistor is shorted, the flippers will always work even when the game is over). There are also two jumpers W4 and W5 on the driver board which should NOT be installed (if these jumpers are installed, the flippers will always be activated, even when the game is over).
        Fliptronics Games:
        • Check the flipper fuses on the Fliptronics board.
        • Use the internal WPC test software to test the flipper switches. Press the "test button", and go to "Test Switch Edges". A matrix chart will appear. The flipper switches are connected directly to the CPU board (on WPC-95) or the Fliptronics board (on earlier games) through direct switches, and not through the switch matrix (non-fliptronics games have the flipper switches and EOS switches wired directly to the flippers, and don't connect to any board). This means if the flipper button is pressed on any Fliptronics and later game, the circles on the right most column (outside the box) of the matrix should change to a square. Here is the order for that matrix column, from top to bottom:
          • Lower Right Flipper EOS switch
          • Lower Right Flipper button
          • Lower Left Flipper EOS switch
          • Lower Left Flipper button
          • Upper Right Flipper EOS switch
          • Upper Right Flipper button
          • Upper Left Flipper EOS switch
          • Upper Left Flipper button
          If the EOS switches aren't working on a Fliptronics or later game, check the continuity with a DMM from the switch to the CPU board (on WPC-95), or the Fliptronics board (on earlier games). On pre WPC-95 games, these direct EOS switches go to the Fliptronics board connector J906 and the flipper opto switches go to J905. On WPC-95 games, the direct EOS switches go to the CPU board connector J208 and the flipper switches go to CPU board connector J212. Non-fliptronics games have the flipper switches and EOS switches wired directly to the flippers, and don't connect to any board.
        • On fliptronics games, if the flipper button doesn't register in the above test, check the flipper opto boards. Flipper opto boards were implemented on Addams Family, mid-production (some Addams have them, some don't). Also if the game uses plastic flipper opto activators, often these can warp. This will cause the activator to not clear the "U" shapped opto on the flipper opto board, causing a flipper to never energize!
        • On fliptronics (before WPC-95) games, there can be a very rare and unusual problem with the fliptronics board. There is +50 volts power at the flipper coils (and the coils & diodes are good), but flipper switches just don't seem to work. This can be caused by a failed flipper switch input chip at location U5 (74HCT244) on the fliptronics board.

    Optos are used on fliptronics
    flipper switches. Note the plastic
    activator arm that moves between
    the "U" shaped optos. Originally
    Williams made these from metal,
    but switched to plastic to save
    money. The plastic version can
    often warp so they don't clear
    the opto, causing a flipper not
    to work.

    flipper switch optos

      If the flipper button works fine in diagnostics, but the flipper doesn't work...
        All WPC Games:
        • Check for +50 volts at the flipper coil. Put the DMM on DC voltage. Put the black lead on ground (metal side rail of game). Put the red lead on either of the outside lugs of the coil. A reading of 50 to 80 volts on either lug should be indicated. No voltage means (the coin door is open on 1993 or later games or) a fuse is blown, or a wire has broken.
        • Test the coil itself. To do this, turn the game on and leave it in attract mode. Then attach an alligator test lead to ground (metal side rail of game), and momentarily touch the other end of the test lead to the middle lead of the flipper coil. The coil should activate. This works on both Fliptronics and non-Fliptronic WPC games.
        • Check the flipper coil with a DMM set to ohms. With the game turned off, try this:
          • Notice the three solder lugs for the flipper coil. One of the outside lugs has both a thick and thin coil winding attached to it. This is the "common" lead.
          • Put one lead of the DMM on the outside common flipper lug (the one with the thin and thick coil windings attached to it).
          • Put the other lead of the DMM on the middle lug. A reading of about 4 ohms should be indicated. This is the high powered side of the coil.
          • Put the leads of the DMM on the two outside lugs of the coil. For fliptronics games, a reading of about 125 ohms should be seen. For non-fliptronics games, a litle more than 4 ohms should be seen until the the flipper is moved manually to the full extended position, opening the EOS switch. Now about 125 ohms should be indicated.
          • If approximately these readings are not seen, the flipper coil is bad. Typically the hold side of the coil goes bad more often that the power side.
        • Test the flipper diodes. To do this cut one lead of each diode off the coil lug. Then set the DMM to the diode setting. Put the black lead of the DMM on the banded side of the diode. A reading of .5 volts should be seen. Reverse the leads and no (null) reading should be shown. When done, re-attach each diode lead.

      If the flipper works, but...

        Non-Fliptronics Games:
        • Flipper seems to work fine, but gets very hot and eventually starts to burn and smell. Often the flipper will get stuck in the "up" position. On non-fliptronic games, the EOS switch contacts are not opening when the flipper is fully extended. Or the EOS switch capacitor has shorted on.
        Fliptronics Games:
        • When activated, doesn't hold up (the flipper "flutters"). This means the hold TIP102 transistor for that flipper is bad, or the hold winding on the coil itself is broken. The hold winding on the coil is the thin wire. If it is broken, usually the wire has broken away from one of the solder lugs (the middle lug should have both the thick and thin wire attached to it). Test the coil first (see above) before replacing the transistor.
        • Flipper coil gets really hot after playing the game for a while. This is often a dirty flipper optic on the flipper board next to the flipper buttons. It could also be a bad LM339 chip at U4 and/or U6 on the Fliptronics board (or U25/U26 on a WPC-95 CPU board). An easy way to see if it's the LM339 chip or the optics is to swap the two flipper optic boards, and see if the problem changes to the other flipper. A dirty flipper switch "U" optic can essentially cause the flipper button to automatically turn on and off quickly (even when the player is not pressing the button), making the flipper coil warm.
        • Flipper seems to work fine, but gets very hot and eventually starts to burn and smell. Often the flipper will get stuck in the "up" position. On fliptronic games, the hold TIP102 transistor for that flipper is shorted on, and needs to be replaced.
        • When a game is started, all the flippers activate for a moment, then go dead. This can be caused by having the flipper switch board connectors removed from the Fliptronics board. With the connector removed, the game thinks all the flipper buttons are pressed. The flippers go dead because the secondary 50 volt power fuse blows.
        • The flipper stays up for a moment after the flipper button is released. This happens on fliptronic games that have plastic activators which activate the flipper board optos. Sometimes the plastic's elasticity is lost, causing it not to spring back quickly when the button is released. Replace this plastic flipper activator. A temporary solution is to stretch a rubber band across the back of the plastic activator for additional tension. Flipper opto boards were implemented on Addams Family, mid-production (some Addams have them, some don't).
        • Flippers work fine, but the flipper buttons do not work in video mode or high score entry mode. On games with flipper optic switch boards, there are two "U" shaped optic on each board. Games with 2 or 3 flippers often use one of the two "U" optics for the flippers, and the other for video mode and high score entry. This problem could be caused by this second "U" optic being bad, dirty, or there is a problem with the plastic activator not clearing the second "U" optic.

      If one or both flippers are weak...
        Non-Fliptronics Games:
        • Rebuild the flippers. Play and wear in the flipper parts is the primary reason for weak flippers. A mushroomed flipper plunger dragging against the coil sleeve is a classic cause of weak flippers.
        • Make sure there is about 1/16" up and down play on the flipper. To test this, from the top of the playfield, grab the plastic flipper and pull up. There should be some play. If not, the flipper could be binding on the nylon playfield insert. This gap is adjustable from under the playfield by changing the flipper pawl's grip on the flipper shaft.
        • Make sure the EOS (end of stroke) switch is properly adjusted. On non-fliptronics games, the EOS switch should open no more than 1/16" to 1/8" at the end of the flipper stroke. If the EOS switch is misadjusted, this can cause a slightly weaker flipper on old and new WPC games.
        • On non-fliptronics games, file clean the EOS switch contacts and the cabinet flipper switches. These are high-voltage tungsten switch contacts, and a metal file will be needed to clean them. These switch contacts often become pitted and tarnished, and resistance develops, weakening flippers.
        • Check the flipper power connections. On non-fliptronics games, this is connectors J109 and J110 on the power driver board. Make sure the solder joints on these board header pins are not cracked, and that the connector and header pins are in good shape.
        • Check the bridge and capacitor that supplies voltage for all coils (BR3 and C8). An open diode in the bridge rectifier that supplies power to the flippers can cause weak flippers. A fatigued or cracked solder joint on this bridge (or its associated capacitor) can do that too. Soldering jumper wires from the bridge to its associated capacitor is a good idea. This is rare, but does happen. This problem will effect BOTH flippers equally. See the section, Testing Bridge Rectifiers for more information.
        Fliptronics Games:
        • Rebuild the flippers. Play and wear in the flipper parts is the primary reason for weak flippers. A mushroomed flipper plunger dragging against the coil sleeve is a classic cause of weak flippers.
        • Make sure there is about 1/16" up and down play on the flipper. To test this, from the top of the playfield, grab the plastic flipper and pull up. There should be some play. If not, the flipper could be binding on the nylon playfield insert. This gap is adjustable from under the playfield by changing the flipper pawl's grip on the flipper shaft.
        • Make sure the EOS (end of stroke) switch is properly adjusted. On games with electronic flippers (fliptronics), the EOS switch should close right at the end of stroke, and not prematurely. If the EOS switch is misadjusted, this can cause a slightly weaker flipper on old and new WPC games.
        • On WPC fliptronics and later games, try cleaning the "U" shaped optics on the cabinet flipper opto boards. Use a Q-tip and some Windex to clean them. Also make sure the opto activator bars fully clear the optos when the cabinet switch is pressed. If one weak flipper still exists, try swapping the cabinet flipper opto boards (remember, both flipper boards must be plugged in for this to work!). If the weak flipper problem moves to the other flipper, the opto board's optic has become faulty, and it will need to be replaced with a new "U" shaped optic. A marginal cabinet flipper board optic, even if clean, can cause a weak flipper. Replace if in doubt. Also check the opto switch with your multimeter. With the game on and your meter set to DC volts, on the flipper opto board measure the connector pin marked SW1 and SW2 against ground. A measure of below 0.7 volts (below 1V is OK) should be shown, with the button pressed. A higher reading means a dirty or defective opto switch. If cleaning does not remedy the problem, replace the opto switch. NOTE Later WPC-95 pinballs use a Schmitt Trigger opto switch (3 legs on the receiver, 2 on the transmitter) which eliminates this problem. The Schmitt trigger optos will not oscillate (turn on and off quickly, making the flipper weak) when the optics gets dirty. They usually either work, or don't work.
        • On WPC fliptronics to WPC-S, replace the U4 and/or U6 LM339 chips on the Fliptronics board. On WPC-95 games, replace U25 and/or U26 on the CPU board (since these games don't have fliptronics boards). Although these don't fail often, then can cause weak flippers. See "WPC Fliptronics Flipper Optos" in the switch matrix section for more details.
        • Check the flipper power connections. On WPC fliptronics to WPC-S games, this is connector J907 and J902 on the fliptronics board. On WPC-95 this is connectors J119 and J120 on the power driver board. Make sure the solder joints on these board header pins are not cracked, and that the connector and header pins are in good shape.
        • On WPC fliptronics to WPC-S games, check the fliptronics board bridge rectifier (BR1). On non-fliptronics games, check the bridge and capacitor that supplies voltage for all coils (BR3 and C8). An open diode in the bridge rectifier that supplies power to the flippers can cause weak flippers. A fatigued or cracked solder joint on this bridge (or its associated capacitor) can do that too. Soldering jumper wires from the bridge to its associated capacitor is a good idea. This is rare, but does happen. This problem will effect BOTH flippers equally. See the section, Testing Bridge Rectifiers for more information.

      While playing a game, a flipper gets weaker and weaker. The longer the machine is left on, whether playing or not, the flipper will still get weaker until it won't work at all...
        Fliptronics Games:
        • Dirty optic switches on the flipper board can cause this. Try cleaning them with Windex and a Q-tip.
        • Failing optic switches on the flipper optic board can cause this too. Try swapping the left and right flipper boards. See if the problem switches to the other flipper. Remember, both flipper boards must be plugged in for this to work!
        • On WPC fliptronics to WPC-S games, failing LM339 voltage comparators at U4 and/or U6 on the fliptronics board. On WPC-95 games, replace U25 and/or U26 on the CPU board (since these games don't have fliptronics boards). Although these don't fail often, they can cause weak flippers. Do this as a last resort. See "WPC Fliptronics Flipper Optos" in the switch matrix section for more details.

      Flipper coil gets very hot...
        Non-Fliptronics Games:
        • Check the EOS switch to make sure it is adjusted properly, and that the contacts are clean and filed. The EOS switch should open 1/16" to 1/8" when the flipper is fully extended (on non-fliptronics games).
        Fliptronics Games:
        • On WPC fliptronics and later games, if there is a marginal flipper switch reading, this causes the high powered side of the flipper to rapidly oscillate between on and off. The holding side of the flipper coil never engages. This problem will cause the flipper coil to get very hot in a short time. First try cleaning the flipper board optics. If this doesn't work, the LM339's on the Fliptronics board at U4 and/or U6 (or CPU board on WPC-95 at U25 and/or U26) will need to be replaced.
        • Bad regulation of the 12 volt power to the optos can cause the flipper coils to get hot too. Though rare, the 7812 voltage regulator on the power driver board could be failing, or the electrolytic filter capacitor for the 12 volts.

      Flipper gets stuck in the up position...
      If the flipper is stuck in the up position, turn the game off. If the flipper falls back, the problem is electrical. If the flipper stays up, the problem is mechanical.

        Mechanical "Stuck Up" Problem:

        • Check the EOS switches and the flipper pawl. Often the rubber coating on the flipper pawl that contacts the EOS switch will wear. This causes the flipper pawl to hang up on the end of the EOS switch. The end of the EOS switch can even get torn and fray from this. See "Rebuilding Flippers" for information on fixing this. Also if the flipper coil stop get mushroomed, this will increase the flipper plunger travel. This will make it easier for the flipper pawl to stick on the EOS switch.
        • Flipper too tight inside the playfield flipper bushing. This causes binding between the playfield bushing and the flipper crank assembly. There should be about a 1/32" gap. If the flipper paddle doesn't have any vertical movement, it's too tight. Use the flipper adjustment tool included with the game to fit this (see rebuilding flippers for more info).
        • Check the flipper return spring. Is it broken or missing?

        Electrical "Stuck Up" Problem:
          Non-Fliptronics Games:
          • Make sure the cabinet flipper switch is adjusted properly, and not stuck closed.
          Fliptronics Games:
          • Flipper cabinet switch is bad. On games with opto flipper cabinet switches, check the two opto boards. A bad or dirty opto can cause this problem. Flipper opto boards were implemented on Addams Family, mid-production (some Addams have them, some don't). On pre-opto flipper switch WPC games, check/clean the mechanical cabinet flipper switch.
          • Flipper gets very hot and eventually starts to burn and smell. This means the hold TIP102 transistor for that flipper is shorted on, and needs to be replaced.
          • Flipper immediately energizes and stays up when a game is started, or when the game turns on. The TIP36 transistor that controls the high voltage side of the coil is shorted on, and needs to be replaced.
          • Addams Family ONLY: The Addams Family pinball was the first Williams solidstate "fliptronics" game. It was the only game to use a "Fliptronics I" board (all later games used a "Fliptronics II" board). The Fliptronics I board has a unique personality. If both diodes on the right flipper coil (upper or lower) are missing or broken, as soon as the right flipper cabinet button is pressed in a game, both right flippers will stick in the "up" position. The right flippers will not release until the left flipper cabinet button is pressed! Note this MAY also happen if one diode on each right flipper coil is bad too. This problem can also happen to the left flipper, and is still related to coil diode failure. To fix this, check both right flipper coils and make sure the diodes are not broken or missing. Also make sure the left flipper coil's diodes are present and not damaged. Finally, sometimes a bad flipper diode will cause the Fliptronics I board's TIP102 hold transistor to fail. If the problem still exists after replacing the diodes on all the flipper coils, check the TIP102 hold transistor on the Fliptronics board.

      Flipper problems should be addressed by at least one of the above.