Now we need to test the chip that drives the diode and driver transistor. This chip is a CA3081 (NTE916) transistor array. Basically it's several transistors packaged in a chip format. This is known as the "pre-driver transistor pack". You can test this too:
• Turn the game off.
• Remove the Solenoid driver board from the game.
• Put your DMM on diode setting.
• On the component side of the board, put the black lead of your DMM on the GND test point just to the left of the U1 chip.
• Put the red lead of your DMM on the two pins of the pre-driver chip (one at a time) that you noted above.
• For the pin that connects to the 1N4004 CR diode, you should get a reading of .1 to .2 volts.
• For the other pin, you should get a reading of .7 to .8 volts.
• Reverse the DMM leads (red lead now on GND). You will get the same .1 to .2 volt reading for the pin that connects to the CR diode. The other pin will read 1.1 to 1.3 volts. Note this test is far less conclusive than the first test with the black lead on GND.
If you get any other meter readings, replace the pre-driver CA3081 (NTE916) chip.

Replace the Coil Diode.
If you had ANY problems with a coil being locked on, ALWAYS replace the coil diode. This diode prevents a "backlash" of current going to the solenoid driver board when the magnetic coil is shut off. This diode is easily damaged and can cause damage to your solenoid driver board if bad. Always make sure you install the new diode with the diode band on the "power" lug of the coil. The power lug is usually the lug with two wires going to it (because the power is daisy chained from coil to coil).

Testing for Power at the Coil.
If a coil doesn't work, and the transistor is good, test for power at the coil. Do this with the game on and in attract mode, and the playfield lifted.

• Put your DMM on DC voltage (100 volt range).
• Put the black lead on the metal side rail (ground) of the game.
• Put the red lead on either terminal of the coil. It should read about 43 volts. On flipper coils, any of the three terminals should also read about 43 volts.
If you are missing voltage at the coil, check for a broken wire/connector, or blown playfield fuse (see below). Remember the power wires are "daisy changed" together. So a break in the power wire in a previous coil will cause the coils further down the line to not work.

Testing a Coil.
You can also test a coil for proper operation. With the game on and in attract mode, and the playfield lifted, try this:

• Connect one end of a alligator clip and wire to the metal side rail of the game.
• Momentarily touch the other end of the alligator clip to the coil's terminal with the non-banded side of the diode connected to it.
• The coil should fire.
Note if you accidentally touch the banded side of the diode to ground, you will probably blow a fuse.

If the coil doesn't fire, you have a damaged coil or no power at the coil. Look for a broken wire going to the coil's terminal. You can also test the resistance of a coil. A good coil should be in the 3 to 15 ohm range.

The Over-Looked Under-Playfield Solenoid Fuse.
Often your Bally game will boot fine and start a game. The flippers work, but no other solenoids on the playfield work. This can often be caused by a blown under-the-playfield solenoid fuse.

If you run the solenoid diagnostic test and the coin lock-out coils, the flipper relay, and the knocker all work, and nothing else works, a dead under the playfield fuse could be the problem. Since the game boots OK, we know the +43 volt fuse on the rectifier board is OK (if this fuse was blown the MPU board won't "flash" the seventh time).

The under the playfield solenoid fuse is usually located on the right hand side by the flippers. Usually it's a 1 amp slo-blo fuse. If this fuse keeps blowing, you have a solenoid problem on the playfield somewhere. This can be caused by a shorted coil, a bad coil diode, or a broken (and shorted) coil wire. A shorted and locked on driver transistor is probably NOT your problem.

If the playfield fuse keeps blowing, there is another procedure you can try to isolate the problem as a last resort. Turn the game off and disconnect the "pull down" wire from EVERY coil under the playfield. The pull down wire is the single wire on each coil, and connects to the NON-banded side of the coil's diode (the power side connects to the banded side of the diode's coil lug). Then power the game on (the fuse should not blow!). Now re-connect each wire to its respective coil. When the fuse blows, you've found your problem coil/diode.

Coil TroubleShooting - More Ideas.
Here's some other ideas on coil problems.

No Coils Work.

• Check TP5 on the power supply for 43 volts. If no voltage, check fuse F4 on the power supply.
• Check solenoid driver board for +5 volts at TP3 on the driver board. If no voltage here, check for a broken jumper on connector J3 from pin 13 to pin 25.

Only the flippers work.

• Check 1 amp slow blow fuse underneath the playfield.
• Check for a broken wire from the above fuse. There should be a brown wire going from the under the playfield 1 amp fuse to the flipper coil.

Flippers work and just some coils.

• Under the playfield, check for a broken yellow wire from coil to coil. This is the coil power wire, and it daisy chains from one coil to another. A break in this wire will stop power from getting to coils "down stream".
• A problem with the connection between connectors J4 of the MPU board and J4 of the solenoid driver board. If one line is missing, coils 1 to 4 will not work.

Power supply board coil power distribution.

• J1 pin 6 = brown wire to flipper coils.
  
• J1 pin 9 = to solenoid driver board J3 pin 5 (flipper relay).
  
• J2 pin 2 = to chime unit (in early games) or knocker coil (in later games), and coin lockout coils in all games.
• J2 pin 13 = to backbox knocker on early games.
• J3 pin 12 = to MPU board connector J4 pin 15.

Bally's lamp driver and auxiliary lamp driver boards stayed pretty consistant from 1977 until 1989 (when Bally produced its last game, before being taken over by Williams). These procedures should work on all Bally lamp driver boards from their inception until their end in 1989.

If a feature light is continually on, or is never on, you can test the lamp driver board for a component problem. Assuming the wiring is intact, chances are good that the lamp's driving component(s) are bad. This is especially true if a lamp is always on. The internals to the driving components have probably shorted on, leaving the lamp continually on.

All Bally electronic pinball games until Williams bought them out in 1989 used SCR's (Silicon Controlled Rectifiers) to drive feature lamps. SCR's are different than transistors. Instead of a collector, base and emitter like a transistor, they have a cathode, anode and a gate (abbreviated C, A, G respectively, though sometimes the "C" is abbrevated as "K"). Each gate is driven by a CD4514 CMOS decoder output. All SCR cathodes are connected to the feature lamp ground. Each SCR anode is connected to a unique feature lamp.

There are two different SCR's used for lights on the lamp driver board: the larger MCR106-1, and the smaller 2N5060. They serve the same function, just the larger MCR106-1 can handle more current (and sometimes lights two lamps, while the smaller 2N5060 can only light one lamp). There is also a CD4514 CMOS decoder that drives the lamps. Sometimes these go bad too.

Bally does not use a lamp matrix to drive the feature lamps. There is a separate SCR that drives each feature lamp.

Nieuw thyristoren kun je gewoon bij de Flipperwinkel kopen.


Testing the Lamp Driver SCR's, game On.
If a lamp is permanently stuck on, this procedure won't tell you anything. A lamp that is always on is generally caused because its SCR has internally shorted. Replace the SCR.

The Bally red test switch, just inside the game's coin door.

Assuming the game powers on, you can test a non-working lamp's SCR's to see if it's working (this assumes you have checked the bulb, the lamp socket, and the wiring to the lamp socket).
• While the game is on and in "attract" mode, press the Self-Test button inside the coin door ONCE. This should put the game into the "Flash All Feature Lamps" test (check your game manual if it does not).
• Note which feature lamps are NOT working. Write them down. You will need this information if several lamps that connect to the same decoder don't work. A decoder has likely failed if 4, 8 or 12 lamps (multiples of 4) are not working.
• Check the manual's schematics to figure out which SCR controls the lamp(s) in question. This information is on the Lamp Driver schematic page.
• Look at the connectors at the right of the schematic. There the lamp name/descriptions will be listed.
• Follow this line back to the first "Q" (SCR) that intersects this line. Note the SCR number (for example, "Q8"). If the schematic lists a "**" next to the SCR, this means it's a MCR106-1. Otherwise it's a 2N5060. Also note the chip that drives this SCR ("U1"). Both these components could be damaged (but generally it's just the SCR).
• Write down the "Q" number and the lamp name on some paper. Also write down the driving decoder "U" chip number.
• If 4, 8 or 12 lamps that all connect to a single decoder don't work, suspect the decoder "U" chip as faulty.
• Press the game's test switch again to take the game out of lamp test mode. The display test will probaby come up. Leave the game here, as all the playfield lamps should now be turned off.
• Connect an alligator test lead wire to ground. The bare braided wire in the bottom of the back box works well for this.
• Touch the other end of the test lead to the ANODE of the SCR in question. On the large SCR, the metal tab is the anode. On the smaller SCR, it's the lower right leg. To make sure, the pinout for the small SCR's is silk screened on the board for a few selected SCR's. You are looking for the lead marked "A".
• If the lamp does NOT light when the anode is grounded, the problem is NOT on the lamp driver board. Most likely you have a wiring problem, a bad lamp socket, or a bad bulb.
• If the lamp DOES light when the anode is grounded, the problem probably lies with the SCR. Replace it and see if that fixes the problem. If not, suspect the "U" decoder chip that drives that lamp.

Testing the Lamp Driver SCR's, game Off.
You can also check the lamp driver board's SCR's using your DMM, set to the diode setting.

• Check the manual's schematics to figure out which SCR controls the lamp(s) in question. This information is on the Lamp Driver schematic page. Write down the SCR's "Q" number.
• Look at the connectors at the right of the schematic. There the lamp name/descriptions will be listed.
• Follow this line back to the first "Q" (SCR) that intersects this line. Note the SCR number (for example, "Q8"). If the schematic lists a "**" next to the transistor, this means it's a MCR106-1. Otherwise it's a 2N5060. Also note the chip that drives this SCR ("U1"). Both these components could be damaged (but generally it's just the SCR).
• You can remove the lamp driver board, or leave it installed in the game. Use your DMM set to the "diode" setting.

  MCR106-1 Lamp Driver SCR test:

  • Put the black lead of your meter on the outside "cathode" leg (labeled "C") of the SCR.
  • Put the red lead of your meter on the outside "gate" leg (labeled "G") of the SCR. Your meter should read .4 to .6 volts.
  • Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.
  If your meter reads anything outside the values above, replace that MCR106-1.

Testing the large MCR106-1 lamp driver SCR.

2N5060 Lamp Driver SCR test:
• Put the black lead of your meter on the "cathode" leg (labeled "C") of the SCR.
• Put the red lead of your meter on the center "gate" leg (labeled "G") of the SCR. Your meter should read .4 to .6 volts.
• Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.
If your meter reads anything outside the values above, replace that 2N5060.

Testing the small 2N5060 lamp driver SCR.

Starting with Eight Ball Deluxe, Bally started designing games that had more solenoids than transistors to drive them on the solenoid driver board. To allow more coils to be used in the game, Bally came up with a "Solenoid Expander Board". This board is a solenoid multiplexer; it allows a single transistor on the solenoid driver board to drive two different devices, instead of just one.

The solenoid expander board's main component is a relay. This relay connects to four different coils. When the relay is pulled in, two of the four coils can be activated by the solenoid driver board's transistors. When the relay is at rest, the other two of the four coils can be activated by the solenoid driver board's transistors.

The real trick to the solenoid expander board is how its relay is pulled in. A relay is basically a solenoid with switches. To activate a solenoid you normally use a transistor on the solenoid driver board. But wait! We're trying to SAVE transistors on solenoid driver board because we're running out of them to drive all the coils on the game.

So instead of using a solenoid driver board transistor to activate the solenoid expander board's relay, a LAMP driver SCR (silicon controlled rectifier) is used on the lamp driver board! This allows the lamp driver board to control which two of the four coils can be controlled by the solenoid driver board's transistor.

The solenoid expander board and its accompanying 555 lamp.

Another way to look at it is this: think of two transistors on the solenoid driver board, say transistors 11 and 12. These normally control two coils (call them coils 11 and 12). But now transistors 11 and 12 control FOUR coils (coils 11a, 11b, 12a, 12b). When the lamp driver board's SCR activates and pulls in the solenoid expander board's relay, the solenoid driver transistors 11 and 12 control coils 11b and 12b. When the lamp driver board and solenoid expander board's relay are at rest, the solenoid driver transistors 11 and 12 control coils 11a and 12a. Note all four coils can not be activated at the same time.

It's also important to note that the solenoid expander board usually controls little used coils. Stuff like the outhole kicker or drop target reset coils. These coils are used far less than say slingshot or pop bumper coils. So if your outhole kicker solenoid is acting up, the expander board may be the cause.

The Solenoid Expander Board's Partner.
The other strange thing about the solenoid expander board is its partner; a lamp! The solenoid expander board is located under the playfield, and right next to it is a lamp. This lamp is VERY important, and it must have a good light bulb installed for the solenoid expander board to function properely.

The reason for the lamp is this; the solenoid expander board has a MOC3011 opto-isolator that actually turns the relay on. However this device doesn't draw enough current for the SCR on the lamp driver board to activate it. To solve this problem, an actual lamp is installed next to the solenoid expander board. This lamp is also connected to the lamp driver board's SCR. The combination of this lamp and the solenoid expander board's MOC3011 gives the lamp driver board's SCR enough current draw for it to work reliably.

Testing the Solenoid Expander Board.
The easiest way to test the solenoid expander board is to use the built in feature lamp diagnostics. After the game is turned on and in attract mode, press the red test button inside the coin door once. This will activate the feature lamp test. All the playfield lamps will turn on and off. The solenoid expander boards relay should also click on and off. If you lift the playfield you should see the solenoid expander board's relay pull in. You should also see the lamp next to the solenoid expander board turn on and off.

If you heard the relay buzz instead of click on and off, this means there is a problem. See the list of problems below to fix this.

Problems with the Soleniod Expander Board.
If the solenoid expander board buzzes in the above test, this indicates a problem. Also it is important to remember that every coil that connects to the solenoid expander board has TWO diodes; one "normal" diode across the coil lugs, and another diode in series with the power wire going to the coil! If this diode set up is mis-wired, a diode is reversed, missing or broken, you will have problems. Here are some other things to consider too:

• Header pins on the solenoid expander board may have cracked solder joints. Re-flow these header pin solder joints.
• The lamp under the playfield next to the solenoid expander board may be burned out. Replace with a new lamp. Without this lamp, there isn't enough load for the SCR on the lamp driver board to activate the solenoid expander board's relay.
• The lamp driver board's SCR that controls the solenoid expander board may have failed. See Locked-On or Not Working Feature Lights (lamp driver board) section for details on how to test the SCR.
• The 6.5 volts provided by the power supply's rectifier board BR1 bridge may be failing. The 6.5 volts DC provided by BR1 powers the feature lamps. If this voltage is low, the solenoid expander board's relay may not function correctly.
• The power supply's rectifier board R2 resistor (25 ohms 5 watts) may be broken or open. Check it with your DMM set to ohms.
• Connector pins on the power supply's rectifier board may be burned or tarnished. This will create resistance which will lower the 6.5 volts DC provided to the lamp driver board. If this voltage is low, the solenoid expander board's relay may not function correctly.
• Diode on the solenoid expander board's relay may be broken or missing.
• In-series diode going to the power lug of the coil may be broken, missing or reversed.
• Diode across the lugs of the coil may be broken, missing or reversed.
• Switch contacts on the solenoid expander board's relay may be pitted and may need to be filed (or the relay replaced).
• The solenoid expander board's MOC3011 opto-isolator may be bad. Replacements are available from Jameco (part #95020), or replace with NTE3047.

Testing the Transistors and Coils Driven by the Solenoid Expander board.
If the solenoid expander board's relay is working properely, you can test the devices it controls using this test:

• Check the schematics to see which transistor number is controlled through the solenoid expander board.
• Turn the game on and let it boot.
• Press the red test switch once to put the game into diagnostic feature lamp test.
• Using an alligator clip test wire, attach one end to the ground strap in the backbox.
• Touch the other end of the alligator clip test wire to the metal tab on the solenoid driver board's transistor you identified in the first step above.
If you leave the transistor's metal tab grounded while the game is in the feature lamp diagnostic test, the two coils controlled by the above transistor should turn off and on with the feature lamps.

Left: the earlier style AS2518-43 Auxiliary Lamp Driver board.	Right: the later style AS2518-52 Auxiliary Lamp Driver board.

On Bally games with special backbox lighting (Space Invaders, Xenon, and many others), Bally used an auxiliary lamp driver board to run these lights. This saves the lamps on the lamp driver board for use on the playfield. This auxiliary board isn't much different than the lamp driver board itself. It used SCR (silicon controlled rectifiers) just like the lamp driver board. It uses only MCR106-1 devices (no 2N5060 SCR's).

If a lamp is locked on or not working that is controlled by the auxiliary lamp driver board, the procedure for testing and replacing its SCR on the auxiliary lamp driver board is the same as the lamp driver board. Please see lamp driver board section above for more details.

All electronic pinball machines use a technique to read switches called a "switch matrix". Problems with the switch matrix can be difficult to diagnose. The matrix consists of eight rows and eight columns. This makes a checkerboard type pattern with 64 individual switch (or squares). So instead of 64 wires going to 64 switches, there are only 8+8=16 wires going to all the switches.

Bally identifies the switches in the switch matrix starting with row zero, column zero as switch "1". The rest of the switches in column 0 are numbered 2 through 8. If you look at the schematic it can appear some switches are missing. But most of these "missing" switches are the cabinet switches, which are not shown on the schematics. This includes the ball roll tilt, the plumb bob tilt, and some other cabinet switches.

Stuck Switches.
If a switch is stuck, first remove all the balls from the playfield (to open the trough switches). Also if a switch gets closed as you lift a playfield up, put a piece of tape between the switch contacts to prevent closure. This especially happens on spinner targets.

Put the game into its switch test. On games with sound cards (Lost World and later), this means pressing the red self-test button inside the coin door FIVE times. For chime games prior to Lost World you only press the test button four times. Note the switch number shown in the display. This will be the last switch "bad switch" in the list. Use your game manual to find the actual playfield location of the switch. Clear this switch first, then the next "bad switch" will be shown on the display. Your job isn't over until there are no more switch numbers shown in the display.

Switch Capacitors - Stuck Switches and Chattering Pop Bumpers.
The most common stuck switch problem relates to the capacitor on playfield switches. Note all playfield switches have a capacitor, but most do. Often these capacitors short, leak, or just break off. With the game on and in switch test, cut one end of the capacitor and see if the number goes away on the display in switch test. If so, the capacitor will need to be replaced. If the number doesn't go away, then reconnect the capacitor, as this wasn't the problem (check the switch diode next, in the same manner).

Note Bally never sent out a service bulletin telling operators to "clip the caps". Many operators did this though to get their game working. Bally only suggested clipping the caps to trouble shoot a stuck switch problem.

Bally used really cheap switch capacitors that failed prematurely. This probably happened because of the high power industrial soldering irons used on the assembly line. The caps used for the switches were actually made for circuit boards. As a result the high powered soldering irons on the assembly line weakened the cap's internal insulation, causing it to leak (not function reliably). This could result in a stuck switch indication. The other problem was the capacitors' leads were weakened from the high powered soldering irons. This caused the caps to break off the playfield switches.

Chattering pop bumpers is another problem caused by bad switch capacitors. A failing switch cap across the pop bumper switch is very common (due to vibration of the bumper), and can cause the switch to "bounce". This will can make the pop bumper fire more than once. Cut the cap off the pop bumper, and see if that fixes the problem. But make sure to replace the capacitor. It is there to help the game detect quick switch closures, and effectively makes the pop bumpers play better (more sensitive).

The switch capacitors are .05 mfd, 16 volt (or greater), ceramic disc, non-polarized.

Non-Working Switches.
There can be a few reasons for a missing switch in the switch test diagnostics. If it is only one switch, it could simply be a broken wire or dirty switch contacts. If it's more than one, it could be a broken wire at the top of that switch string. Switches are "daisy chained" together. That is, a row or column wire runs to the first switch in the series, then continues along to the next. If the wire is broken, all the switches behind that break can be affected.

Connectors can also be a problem. All switches run to the MPU board's J2 connector (upper right hand corner). Connector pins can break, or the wire inside the connector can break.

Switch Diodes - Stuck and Flakey Switches.
Just as the switch capacitors can fail, so can the switch diodes. Though not as common a problem, these small diodes can quite often fail or work intermittently. Unlike the switch capacitor, every switch must have a diode. If the diode is missing or fails, the switch will not work correctly.

Switch diodes are 1N4148 (or 1N914), which are known as fast "switching" diodes. Also a 1N4001 or 1N4004 can be used in a pinch. And it does matter which way the band of the diode is installed!

With the game off, you can test a switch diode by unsoldering one lead of the diode, and use your DMM (set to diode setting), and test the diode. In one direction you should get .4 to .6 volts. Reverse the leads and you should get a null or zero reading.

You can also test a diode with the game on and in switch test mode. Do this by jumping the two switch wires together (before the diode). If the switch registers in the self-test, the diode is bad.

What are the Diodes for?
The diode on each switch isolates that switch from the other switches in the switch matrix's column. The diodes "steer" the signal in one direction only. A shorted, broken, leaky or missing diode can havoc in the switch matrix. A broken diode would cause a switch to never be "seen" by the MPU (a broken wire will cause this too!). A shorted diode will violate a switch's uniqueness, and allow the switch strobe signal to show up at the wrong times, and for the wrong switches! Leaky diodes can act some of the time like a shorted diode, and other times be OK. This is the hardest diode problem to locate, but luckily doesn't happen too often.

Using diodes allows the switch matrix to use only 16 wires for 64 switches. The matrix is made up of 8 rows and 8 columns, allowing for a total of 64 switches. But a problem exists in Bally's design; they don't use diodes on every switch!

The reason Bally did this was they felt diodes were not needed on the coin mech switches. Since a coin mech switch would only be activated by itself (and never during game play with the playfield switches), they were un-needed. Also some early Bally electronics game playfield switches are also missing diodes. These were omitted because it was thought the ball could only activate one switch at a time.

Missing Diodes: the Problem.
If any of the switches without diodes get stuck closed (for whatever reason), this sends a constant signal to the MPU which totally confuses it. This can cause all kinds of other random game play problems. Bally finally reconized this problem, and put diodes on ALL switches by the mid-1980's. If your game is missing any switch diodes, I recommend you install a 1N4148 or 1N914 diode on the switch. Orient the band on the diode as it is installed in the other switches.

Switch Matrix Problems caused by the Coin Door Credit Button.
The start (credit) button is insulated from the grounded coin door with a piece of gray "fish paper". This paper stops the start switch from being permanently grounded. Often this paper gets worn, ripped or torn. This will cause the start button's entire switch strobe (row) to be grounded. This can make your Bally/Stern game do some weird stuff!

If your game has been broken into and the coin door pried open, the start button's fish paper can be easily damaged and causing a switch matrix problem.

For example, one strange problem seen from the start button being permanently grounded was the player one display always showed the same information as the credit/ball display. If the start button gets grounded, other strange game behavior can happen too like a confused game that just won't play right.

If you think the start button may be causing a problem, turn the game off and unplug the coin door's connector plug. Then turn the game back on and see if that clears the problem.

Switches as Interpretted by the MPU.
When a switch is closed, a row and column is crossed. This information goes to the MPU through the wiring harness to the MPU connector J2. Then the U10 PIA chip interprets this signal and directs it to the U9 CPU. Now scoring or other game conditions occur.

The information can get sent to the MPU properely, but a corroded MPU board can mis-direct the information. If acid damage gets underneath connector J2, this can cause havoc. Also connector J3, which at pins 2 and 3 are the shared strobe signals from J2, can be shorted together from corrosion damage and cause more havoc.

MPU Board DIP Switch Problems.
There is another area where the switch matrix can go crazy. This is at the MPU board's 32 mini DIP switches. These switches too have diodes, but if one diode goes bad, the DIP switches can be mis-interpretted, and this can cause havoc in the switch matrix.

If you suspect the MPU board's DIP switches as a problem, just turn them all OFF. This essentially removes them from the switch matrix. Then the DIP switch's diodes can be individually tested using your DMM (set to the diode setting). With the game off, you should get a reading of .4 to .6 for each diode, and when the DMM leads are reversed, a zero or null reading.

Multi-Ball Games and what is Required to Start a Game.
Some Bally multi-ball games require ALL the pinballs to be in the right place before a game will start. If a pinball is stuck or missing, often the game will not start. Sometimes a wire coming off the trough switch can also cause this problem. In either case the game appears to be broken, when the fix is really just unsticking a ball or re-attaching a trough switch wire. Here are the games that are effected by this:

The above switches can be checked in diagnostic switch test. On games with sound cards (Lost World and later), this means pressing the red self-test button inside the coin door FIVE times. For chime games prior to Lost World you only press the test button four times. If the above switches are mis-read by the MPU, this can cause a game to not start, more than one ball being served to the shooter lane, no multi-ball, or some other strange behavior.

The high voltage section of the Solenoid driver board supplies high voltage to the gas score display tubes to light them.

Adjust the High Voltage down to +170 Volts DC.
Bally and Stern games from 1977 to 1985 have an adjustable high voltage potentiometer ("pot") on the Solenoid driver board. This pot is located in the upper left corner of the board, beneath capacitor C26, and to the left of capacitor C23. This pot allows you to adjust the voltage going to the score displays for optimum voltage. Bally recommends this voltage be adjusted to +190 volts DC. But for increased display life, it's best if you adjust the voltage to +170 volts, or as low as +155 volts. Brightness generally won't be effected since there is a minimum voltage required for the gas inside the score displays to glow. Set your high voltage to whatever value it takes to adequately light all of your score displays, then turn it up just a few volts higher. Keeping this voltage as low as possible will greatly extend the life of these gas display tubes, and the display drive circuits.

The high voltage adjustment pot on the Solenoid driver board.

How do I measure the High Voltage?
The high voltage can be measured on the solenoid driver board. Put your DMM on DC volts, and put one lead on the solenoid driver board's TP-2 test point. Put the other lead on ground. This will measure the output high voltage from the solenoid driver board.

Exception to the +170 volt High Voltage Rule.
When installing brand NEW score displays, it may require the full +190 volts DC to light the displays for the first few hours. After the new displays become "seasoned", you can back the voltage down to +170 volts or lower.

High Voltage Warning.
WARNING! The high voltage circuit contains a large capacitor at C26 which can retain high voltage at dangerous levels. This capacitor will bleed off this high voltage to a relatively safe level after the game has been off for a few minutes. Note this voltage can also be dangerous to the integrated circuits on the solenoid driver board. If you short this cap accidently to the logic circuit, it can ruin those components.

Rebuilding the High Voltage Section.
If your high voltage section of your Solenoid driver board is not working, you may need to rebuild it. This is pretty easy to do, and fairly inexpensive. But you should install ALL the parts mentioned below. The design of this circuit was very simple to keep costs low. There is no protection against multiple part failures. Often the parts in this section fail in pairs. So just replacing one will burn out the new part in a short order. So replace all the parts in this circuit to ensure reliability.

High Voltage Rebuild Parts Needed.


• 2N3584 transistor at Q21 (250 volts, 2 amp, TO-66 NPN).
• (2) 2N3440 transistors at Q22, Q23 (250 volts, 1 amp, TO-39 NPN).
• 1N5275A zener diode at VR1 (140 volts, 1 watt).
• 1N4004 diode at CR21 (400PIV, 1 amp).
• 3/16 amp fast blow fuse at F1.
• 22k ohm 1/2 watt resistor at R51.
• 1.2k ohm 1/4 watt resistor at R55.
• 82k ohm 1/2 watt resistor at R56.
• 8.2k ohm 1/4 watt resistor at R54.
• 390 ohm 1/4 watt resistor at R52.
• 100k ohm 1 watt resistor at R35.
• (2) .01 mfd 400 vdc metal polyester capacitors at C27, C28.
• 25k ohm potentiometer PC mount at RT1
You can probably get away with not replacing all the resistors. But make sure you check them all with your DMM. If more than 5% out of spec, replace. It is very common for a resistor to go open in this circuit. Remember to install the new resistors and transistors slightly above the circuit board to allow a good air flow. Re-use any transistor spacers from the old transistors; they help prevent solder shorts. Definately replace all the transistors and diodes and capacitors specified above, regardless if they test good.

Replacement for the 2N3584 Transistor.
Often the high voltage 2N3584 transistor just can't be found. If your high voltage section is showing really high voltage (like 230+ volts), often the 2N3584 and the 2N3440's have failed. The 2N3440's are easy to get. So what can be used to replace the hard to get 2N3584?

There is a replacement transistor, the BUX84. This transistor has a TO-220 style case (instead of a TO-66 case). You may need to enlarge the heat sink's base/emitter holes to make sure there is plenty of clearance for the new BUX84's base and emitter leads. You can also cut off the BUX84's collector (center) lead. You can do this because the BUX84's metal tab, which bolts to the circuit board, will provide the transistor's collector connection. Remember to also insulate the heat sink from the transistor's (collector) metal tab. Use a nylon washer between the transistor's metal tab and the heat sink. Also use a small piece of heat shrink tubing to go over the bolt that holds the transistor to the heat sink.

Testing Your Work.
After the new parts are installed, set the high voltage adjustment pot to the minimum value (turn all the way to the left, counter-clockwise). If the solenoid driver board is the later design, do NOT install the the solenoid driver high voltage fuse!

Now turn the game on and measure the high voltage at TP2 on the solenoid driver board. Now adjust the voltage to +170 volts (or lower, if you can).

Now turn the game off and wait a minute or two for the voltage to bleed off. Re-install the solenoid driver board's 3/16 amp fuse at F1.

Finally, turn the game back on and press the red test button switch inside the coin door twice to run the display test. Let this test run for a few minutes, and make sure all the displays work properely. Check the high voltage again at the solenoid driver board's TP2 to verify everything is Ok.

The "Short" High Voltage Fuse.
The fuse used on the AS2518-22 solenoid driver board for the high voltage section is a smaller 8AG fast blo 3/16 amp style fuse. These are sometimes difficult to find in the smaller 8AG style. If you can't find this fuse, you can solder in a normal 1 1/4" fuse length fuse holder, and use the easier to get 3AG (1.25") fuse.

Replacing the small .75" 8AG fuse with a larger 1.25" fuse. If you can't find a 3/16 amp .75" 8AG fuse, you can solder in a normal size fuse holder in it's place (or bend the existing fuse clip, as described below). The larger 1.25" long fuses are much easier to find.

Another alternative is to bend the fuse clip slightly to accomodate the longer 3AG (1.25") fuse. This can be done by pinching the right angled ends of the stock fuse holder straight. These right angled ends stop a longer fuse from fitting in the smaller fuse holder. When the ends are bent back, the longer 3AG (1.25") fuse fits in the stock holder quite well.

Note the earlier AS2518-16 solenoid driver board does not have this fuse. Also the earlier solenoid driver board AS2518-16 (without the fuse) is directly interchangable with the later AS2518-22 solenoid driver board (with the fuse).

The score displays on these older Bally games can be very tempermental. Here are some tips to help keep them running.

Display Missing One Digit.
If one digit is missing on a 6 digit score display, this can often be caused by a failed resistor. An open resistor at R1, R3, R5, R7, R9 or R11 (on 6 digit displays) are often the problem. If one is found bad (using your DMM set to ohms), replace them all!. They are all 100k ohm resistors. Replace with 1/2 watt versions, instead of the factory installed 1/4 watt size. When installing the new resistor, make sure to leave them slightly above the circuit board for better air flow. Also clean off all the black soot that is attracted to the displays with a 2 inch paint brush.

A 6 digit Bally display and circuit board.

Dim Score Displays.
Sometimes the score displays can seem dim. This is often caused by resistors on the score display circuit board. There are many resistors on this board. Test them with your DMM to make sure they are have correct values. Also make sure the header pins and connector pins on the score display board are clean and bright. If they are not, this adds resistance which dims the displays. To correct this, the pins must be replaced. Also sometimes the header pins can have cracked solder joints on the score display circuit board too. Resolder these to correct this problem.

Bally and Stern Display Units - Interchangable?
Six digit Bally and Stern display units are indeed interchangable. But the seven digit displays are not! But you can modify a Bally or Stern 7 digit display to work in either game.

To do this, jump together pins 11 and 12 of the Bally or Stern 7 digit display with a short piece of wire. This will allow either 7 digit display to work in either game. There is one problem with this, because the Stern display circuit board is deeper than a Bally board. To make this work, you must remount the tray-like mounting bracket on the other side of the backbox door. If you are using a Bally 7 digit display in a Stern game, be careful of shorting the circuit board to the metal bracket since the board will not reach the rubber support buttons at the rear of the bracket.

Finally, the Stern 7 digit display units do not have the circuitry to drive the commas in the display tube. So if installed in a Bally game, the Stern 7 digit display will never show any commas. If a Bally 7 digit display board is installed in a Stern game, the commas will show up! This happens because the commas are generated on the display board and is not part of the data sent by the MPU.

Flickering Displays.
Flickering displays can often be attributed to cracked solder joints or a broken lead on a component. Here are some things to check:

• Pin 36 on the display glass.
• R21, R22, R29.
• Q17.
• U1 pin 13.
Often reflowing the solder joints on these components will fix the flickering problem. Also reflow ALL the header pin solder joints. These crack easily from plugging and unplugging the cable.

The header pins on a score display circuit board. These often need resoldered to fix flickering displays.

MPU board problems causing Score Display Problems.
If data from the MPU board is not properely sent to the score displays, this can cause a display not to work. Often the culprit is chip U20 on the MPU board. Move the score displays to a different player to isolate and make sure the problem does not lie within the score glass itself.

Test Counting Sequence Out of Numeric Order.
If during the score display internal test, the counting sequence is strange (i.e. 0,1,0,1,4,5,4,5,8,9 instead of 0,1,2,3,4,5,6 etc), there could be a problem with one of the address lines not being read correctly. If the problem moves when you swap displays, this means the MPU board is not the problem. Often the resistors R49 to R53 (20k) can be the problem (should be within 5% of 20k ohms), but also check for cracked solder joints at the header pins (a VERY common problem). The interesting thing is a bad display can affect the other displays. You may have to issolate the displays to find the bad one by plugging them into the game (with the game off) one at a time, and then running diagnostics.

Replacing a Score Diplay Tube.
Score display tubes don't last forever. With time and usage, the displays often "outgas". There is no way to fix this short of replacing the glass display tube. Here's how to do it:

• Cut the pins on the old score display tube. Do NOT try and save the old glass! The circuit board is what you are trying to save, not the (bad) glass.
• Remove the old tube's pins from the circuit board. Do this by heating each cut pin, and pulling it out with needle nose pliers. Then use a solder sucker to remove the old solder from the circuit board holes.
• Install the bottom mounting bracket if it was removed for cleaning!
• Feed the new display tube pin into the circuit board starting at one end of the board. This is easiest if all pins are straight first.
• When all the pins have been inserted, carefully bend the tube pins to produce a strain relief bend in all of the pins. This takes a bit of practice so that all the pins don't slip out of the holes in the circuit board! This is very important because as the display tube heats up, the tube can fail where the pins enter the glass if there isn't good strain relief.
• Check display tube alignment before soldering. The bottom plastic display bracket must be installed to check this. If you screw this up, the score digits may not be fully visible through the backglass score windows! Compare your new display to an existing display to make sure things are correct.
• After aligned, gently clamp the tube in place with 2 wooden clothes pins.
• Tack solder the display pins at each end of the circuit board. Re-check alignment.
• Solder all the display tube pins to the circuit board. Make sure the pads are soldered good on both sides of the circuit board. Inspect for any shorts between two pins.
• Clip off the excess display pin leads.
• Inspect again for shorts.
• Put two marble sized dabs of silicon adhesive on the circuit board on both ends of the display glass. Do NOT fully glue the glass to the circuit board!
• Put a big dab of silicon on the display tube's "nipple". This will protect it from breaking and ruining the glass.
• Let the silcon dry overnight and re-install the display.

The sound board discussed here is the Bally "Squawk and Talk" (S&T) board, as used in most of their talking games.

Bad Speaker?
This happens more often than you think. A bad speaker, or a speaker with one broken lead can drive you crazy thinking the sound problem is a lot more complicated. Check the speaker first before proceeding.

Distorted Sound and Humming.
Dried out capacitors on the S&T board is the major cause. The biggest offenders are the final filtering capacitors at C16 and C22. These are 4.7 mfd 25 volt caps, but they should be replaced with 6.8 mfd 16 volts (or higher volts). Here's are the caps to replace:

• C16, C22 (4.7 mfd, but replace with 6.8 mfd 16 volt)
• C19, C24, C25, C28, C31, C34, C42 (1.0 mfd 25 volt)
• C15 (10 mfd 16 volt)
• C36, C43 (2.2 mfd 25 volt)
• C25, C34 (1 mfd 25 volt)
Make sure you install all the above electrolytic caps in the right "direction". They are polarized, and there should be a "+" on the circuit board to help installation.

As a last resort, replace C14 (4700 mfd 25 volts). There generally is no need to replace the big caps at C27 (100 mfd 16 volt), C29 (470 mfd 16 volt), and C34 (4700 mfd 25 volt). Though these are tempting to replace, they are rarely the problem.

If replacing the above caps doesn't solve your sound problem, it can also be caused by a bad U7 PIA chip. This controls execution of speech via the TMS5200 speech chip. You can swap U7 and U11 (same chip) to see if this makes any difference. If it does, that means U7 is probably bad.

Also check the TMS5200 chip at U8 for oxidation on the chip legs, or a poor connection in the socket. This too can cause faulty speech. Sand off any oxidation on the chip legs and reinstall.

Another thing to try is swaping the PIA chips on the MPU board at U10 and U11. Also a bad potentiometer on the S&T board can cause bad speech problems.

Don't forget to check for cracked solder joints on the back of connector J1 on the Squawk and Talk board. This too can cause speech problems.

Checking Your Work.
There is a test button on the S&T board. Note this button is NOT "debounced", and when pressed it makes multiple closures (the switch was not debounced as a cost savings). This can cause the CPU on the S&T board to lock up. Sometimes the S&T board will "stutter" and then lock up. To clear this, turn the game off, and then back on and wait for the game to re-boot. There is no way to avoid the test button bouncing other than luck. The S&T board's self test button should produce several speech phrases, followed by a long single "sound". Then the board will re-boot itself.

The S&T has a series of LED power-on flashes much like the MPU does. Here's a description of the flashes.

First Flicker.
Fakers Guide: No flicker means a bad U5, flakey U15, leaky C1, open R1, leaky CR1, or bad U17.
Techno Guide: On power up, U1 requires +5 volts to be applied before the reset line is allowed to go high. If this condition is met, the LED does a quick "flicker". At power-on, C1 slowly charges via R1. The voltage across C1 is monitored by U15. When it reaches 1.7 volts DC, U15 take the reset line high. Diode CR1 across R1 provides a quick discharge path for C1 in the event the +5 momentarily disappears.

First Flash.
Fakers Guide: No first flash means a bad U6, U15 or U17.
Techno Guide: The U1 chip tests the U6 RAM. It attempts to write then read back all 256 patterns in each of the 128 scratch pad RAM memory locations. If U1 completes the 256 x 128 = 32,768 tests, the LED is flashed.

Second Flash.
Fakers Guide: No second flash means PIA U7 is bad.
Techno Guide: The U1 chip now tests the first PIA U7. Each of the two PIA chips U7 and U11 are interchangable. The test is the same for both. If it determines the two PIAs are good, the U1 chip performs some test. This includes testing each of the two full byte port initialization registers, testing the two full byte I/O registers, and testing the CA2 and CB2 ports. If all checks out, the LED is flashed.

Third Flash.
Fakers Guide: No third flash means PIA U11 is bad.
Techno Guide: The same test above is performed on PIA U11.

Fourth Flash.
Fakers Guide: No fourth flash means sound generator U12 is bad.
Techno Guide: The U1 chip performs a test on the sound generator chip U12. The U12 chip is controlled by PIA U11. If the sound chip passes the LED is flashed the fourth time. A bad PIA at U11 can also cause no fourth flash! Or a bad connection between the three chips U1 (microproocessor), U7 (PIA), and U12 (sound generator).

Fifth Flash*.
Fakers Guide: No fifth flash means speech chip U8 is bad. (NOTE: Some games, namely Fathom, will not have a fifth flash! See the explaination below.)
Techno Guide: The speech generator U8 chip requires an initialization sequence at power-on. Since the chip is a "slow" device, there is an acknowledgement signal from the speech chip to the U7 PIA. Every time a write to the speech chip is done, the speech chip acknowledges. The U7 PIA attempts to send 9 bytes of initialization data to the speech chip, one at a time, waiting for acknowledgement. If it is sucessful, the speech chip is considered functional and the LED is flashed the fifth time. A bad PIA at U7 can also cause no fifth flash! Or a bad connection between the three chips U1 (microproocessor), U7 (PIA), and U8 (speech chip).

*No Fifth S&T Flash on Fathom (and some other games).
Fathom does not use the AY-8912 PSG (Programable Sound Generator) chip at U12 (and has the EE jumpers installed on the S&T board indicating it is not used). Because of this, only *four* flashes of the S&T LED will be seen (after the initial power-on flicker). This is normal and correct. Disassembly of the self-test ROM code for Fathom reveals there are only four calls to the LED flash routine instead of five.

Normal Operation.
The S&T accepts address signals from the MPU to select one of the sound or speech signals stored in memory. It then plays the request by controlling the sound generator chip U12, or the D/A converter U10 for sounds, or the speech generator chip U8 for speech. The S&T is notified of a sound/speech request by an interrupt from the MPU.

Power Needs.
The S&T requires several voltages for operation. A +12 vdc at 3 amps (unregulated) is required for the LED, VR1, and audio amplifier U18. Also +5 vdc is required for the remaining components, and comes from 6.3 vdc through VR2. Also -5 vdc is needed for the speech generator chip, and also comes from the 6.3 vdc input voltage.

Audio Control.
The S&T generates speech via the U8 chip. Commands and speech data are passed to this chip through U7 PIA. The speech chip uses the information it receives to control an electronic vocal tract that produces a speech signal across R14. This signal contains unwanted high frequencies that are removed in a low pass filter through U13, C19, C20, C21, R11, R15, R16, R27 and R81. The filtered speech signal is mixed with an optional off-card audio signal and is given to the speech voltage controlled amplifier (VCA). The output of the speech VCA is fed into the U18 power amplifier (8 watts).

The Squawk and Talk in Technical DETAIL!
Clive Jones wrote and excellent technical document on exactly how the Squawk and Talk works. If you wish to read this document, go to squawk.htm.

No Sound and Loud Buzz from Speakers.
This isn't always a complicated problem. Sometimes no sound and/or loud buzzing from the speakers can be as simple as a bad ground to the sound board. Check the Molex connectors, and make sure the ground wires are making good contact to the sound board.

These are a number of strange problems and solutions that people have mentioned to me.
• "On my Eight Ball Deluxe (EBD), the score displays would flicker during attract mode, and a bit during game play. Also occasionally the flipper would cut out, or the flipper enable relay would chatter. I did all the suggested power supply and solenoid board modifications in this document too."
  The problem turned out to be a bad ground path. The later Bally games used a foil covered cardboard as the grounding method for all the backbox boards. In this case, the foil was not consistently making a good ground to the MPU board. Also the green masking on the back of the MPU board was preventing the board from touching the mounting bracket, so the ground mod in this document did not help. To fix this, wires were run from one mounting bracket on each board to a true ground. Also the green solder mask was scraped from the circuit boards around the mounting bracket. Also make sure the "earth-ground-cable" going to the backbox is connected.
• "On my Elecktra, the player one display does not work."
  The backbox "earth-ground-cable" was mistakenly not connected. Attaching this cable fixed the problem.
• "On my Centaur I recently changed the battery because the game wouldn't remember previous credits. After installing the battery, I went to the self-test button to turn the background sound back on. When I pressed the self-test button, it cycled through the game tests. But the next time I pressed the button to go to the bookkeeping functions, the displays went blank and the game locked up. The game boots just fine and gets seven LED flashes too."
  What has happened is the memory in the 5101 RAM has become corrupt. Replacing the 5101 will fix this problem. Alternatively, you can try grounding all the pins together on the existing 5101. Sometimes that works too.
• "My Bally game works fine except for the flippers. They do nothing. All fuses are Ok, as are the flipper EOS switches."
  This is a very common problem. There is a relay on the solenoid driver board that turns on the flippers during a game. The power to this relay is through brown jumper wires between two header pins, adjacent to the relay. If one of the wires break, comes loose, or their solder points go cold, the flippers will no longer work. On the back side of the solenoid driver board, look for the two brown wires and resolder them to the connector header pins.
• "How do I reset the replay values and high scores?"
  This can be done by pressing the red button on the MPU board when the game is powered on. Note this is the button on the MPU board, not the red (self-test) button inside the coin door!
• "I changed the battery or 5101 RAM on my MPU board, and now the game's sound doesn't work; I only get "chime" sounds, where before I got electronic sound."
  On some 1982 to 1985 Bally games, there are several different types of "sound themes" available. These are kept in memory and not set by a DIP switch. If you change the battery on your MPU board, the game will default to the chime sound. See your game's manual for details on how to change to another sound theme.
• "My Centaur powers on but does not finish 'booting'."
  Centaur is a multi-ball game that requires all balls to be in the ball trough and the ball trough switches working before it will finish its power-on.
• "All playfield solenoids don't work."
  First thing to check is the under the playfield fuse might be blown. Next check fuse F4 on the power supply regulator board. Also check it's fuse clip is in good condition with good tension, and is not brown. Now check TP5 (test point 5) on the power supply regulator board. You should get about 43 vdc. If no voltage at TP5, assume the bridge BR3 on this board is bad and replace it.
  After getting +43 vdc at TP5, then check connector J1, pin 6 on the power supply regulator board. This brown wire goes directly to the playfield flipper coils. If you have +43 volts at the connector, but not at the brown wire on the flipper coils, you have a problem in the wiring.
  Also note, +43 volts on some games is also used on the early A8 sound board (Lost World to Dolly Parton). A problem on this sound board (or a bad connector there) can cause problems.
  If your game is not getting the 7th MPU LED flash, that means +43 volts is missing. If you have checked all the above, verify you have +43 vdc on the MPU board on the left (connector) side of R113. Now check the right side of R113. If no voltage there, then replace R113 (2k, 1/4 watt) and retest. If still no voltage, you probably have battery acid damage in this area on the MPU board.
• "A playfield target feature lamp won't turn off."
  A bad SCR on lamp driver board, or bad capacitor on the switch that activates the lamp.
• "Only even numbered score displays show numbers."
  A bad 5101 on the MPU board can cause this.
• "No game credits shown in the credit display."
  There is a DIP switch setting to turn this back on!
• "Player one display always displays the same information that's in the credit/ball display."
  Maybe a problem with the start button! The start button has a piece of "fish paper" (insulating paper) behind the last leaf. This stops the switch leaf from touching the metal support behind the switch. The fish paper had torn, and allowed the switch blade to touch the metal (grounded) support. This has the effect of grounding a row or column of the switch matrix. This will cause all kinds of strange problems! A new piece of fish paper, and the player one display worked fine.
• "My Bally game boots with 7 LED flashes, but I just can't start a new game, even though I have credits."
  Again, if the grey insulating fish paper on the coin door's start button is worn, ripped, or damaged, this will ground that entire switch matrix strobe (row). This can cause all kinds of strange game behavior.
• "All four of the 7-digit score displays on a 1980 Xenon have the same problem; the first digit and the comma right after it are all dimly lit and visible whenever the displays are on."
  Try disconnecting the score display modules one by one and see if the problem goes away. If so it's related to one of the score display units. If this doesn't correct the problem, most like the problem is the MPU board. Check the MPU board's J1 connector for a poor connection. Also U20 or it's associated components like U11 PIA could be faulty. Try swapping U10 and U11 and see the problem changes. Also check the +190 volts at the display board and make sure it is indeed from 155 to 190 volts.
• "Game starts but won't serve the ball to the shooter lane."
  Make sure there are enough balls in the ball trough, and that all the ball trough switches are working. If that is not the problem, chances are this game uses a "solenoid expander board". This board multiplexes a solenoid driver board transistor so it drives TWO coils instead of one. If the solenoid expander board develops a problem, certain coils may not work. See the section titled Solenoid Expander Board section above for more details.
• "The wrong coil activates."
  Make sure you have the correct game ROM software installed in the MPU board. Aside from that, chances are this game uses a "solenoid expander board". This board multiplexes a solenoid driver board transistor so it drives TWO coils instead of one. If the solenoid expander board develops a problem, the wrong coils can be activated instead of the correct coil. See the section titled Solenoid Expander Board section above for more details.
• "Coil will not work, yet transistor check out good, and there's power at the coil."
  Bad or flakey connector on the solenoid driver board.
• "Can't get the last flash from the MPU (Star Trek)."
  Solenoid fuse on the rectifier board was good, but a bad diode on the sound board lowered the solenoid voltage enough to prevent the MPU from flashing the last time.
• "Solenoids fire "out of order" in the diagnostic test mode."
  Bad PIA on the MPU board. Try swapping U10 and U11 and see if the problem changes. If so, U10 or U11 are bad.
• "Game boots up and everything is "slow" (power up tune is half speed, and there's a delay from when the ball hits a bumper until it scores)."
  Check all passive components that connect to U12, the 555 timer chip. For example, capacitor C16 can go bad and slow the 555 timer frequency, and increase the service interrupt period. This will "slow" the game down.
• "I am working on a Mr/Mrs Pacman, and I notice the GI (general illumination) lamps flash on and off at certain times during attract mode, but does not come on during game play."
  To make the GI lamps flash on and off, Bally used a Triac bolted to the power supply board in the cabinet. The triac is cycled by the GI lamp flasher board mounted under the playfield. This flasher board is similar to a solenoid expander board. The output of a lamp SCR driver is used to drive a MOC3011 opto coupler that drives the Triac. As with the solenoid expander board, a dummy 555 lamp is connected to the SCR output on the flasher board to insure there is enough current draw to drive the MOC3011. Most likely this 555 bulb is burned out, and causing your problem. Also check the flasher board for bad (cracked or cold) solder connections. Check all the cable connections to the triac too. Lastly you can replace the MOC3011 chip.
• "My Xenon won't run with the sound card and vocalizer plugged in. If I unplug the vocalizer from the sound card, and the sound card plugged in, the game works fine (but no sound)."
  Probably a problem with bad capacitors or a bad voice ROM on the volcalizer board. Also check the 3 vertically mounted diodes in the lower right corner of the vocalizer board. When these go bad the diodes run hot and the game has hum and noise. If you replace the diodes, also replace the voltage regulator to the left of them.
• "My Mati Hari displays are strobing wildly. I swapped in a known good driver board, but no change. These displays do not strobe in another game. Game works and plays perfectly otherwise. What is wrong?"
  Connector J1 in the upper left corner of the MPU board could be the problem. Make sure there are no cracked solder joints on the MPU board's J1 connector header pins. This problem could also be related to the rate the displays are being updated. It could be a bad capacitor in the MPU's circuitry for the U12 (555) chip, perhaps the "big green" capacitor.
• "My Bally Space Invaders continues to blow the 20A Fuse for the GI on the Rectifier Board and I'm stumped. It doesn't blow the fuse iimmediately it usually does it shortly after game play begins. Are there any components on the Rectifier Board that may be making it short out? If so what?"
  This is never an easy problem. Break the GI lamp circuits down into sections and isolate the problem that way. Maybe start by disconnecting GI to the backbox, to the cabinet, and/or to the playfield. Eventually you should be able to isolate which part of GI is at fault. Once you've localized it, start disconnecting different portions of the GI circuits on the components in question (playfield, cabinet, backbox). Keep in mind there are two GI lines- red/white, and green/orange. Each one usually runs a couple of lines of bulbs on playfield/backbox. Just start disconnecting a wire from individual lines until problem goes away, then you've got it narrowed down even further. The problem could be shorted wires or sockets, to wires swapped (red to white and vice-versa), even a #44 bulb that had a filament wire sticking out of the bottom of it that was just long enough to short out against the side of the bulb socket when it was installed (this is why I personally like to replace light bulbs with the power on, so you can immediately see a problem bulb). There really aren't any components on the rectifier board that control the GI circuit, unless it's a short on the back side of the board or something. All that really is in the GI circuit on the rectifier board is the 20A fuse. GI power comes off the transformer and goes through fuse. Then it goes to the various pins on J1, J2, and J3, and the test point. Just look for wires rubbing, solder splash on traces/pins on back of board, etc. Of course, if this was the case, then the fuse would still blow even when J1 and J3 were disconnected from the rectifier board. If this isn't happening, then keep looking elsewhere in the game- backbox, playfield, cabinet (coin door), etc.
• "When I turn on my Stern game with a M-200 MPU board, the game will energize coils, blink the lamps, and the displays will count 1,2,3,etc real fast. What is the problem?"
  If all 32 DIP switches on the Stern M-200 MPU board are in the OFF position, the Stern MPU is designed to go into diagnostic test mode at boot-up. So either all your DIP switches are off, or PIA U10 is bad and telling the CPU that all the switches are open (off).
• "My Stern Sea Witch with a M-200 MPU has a problem where it will not boot on occassion. Also the bookkeeping and high score reset button has no effect. There is no MPU board corrosion, and the reset section of the MPU has been totally replaced."
  This person solved their problem by replacing the U9 6800 CPU chip. Apparently the NMI (non-maskable interupt) circuit inside the CPU chip was damaged, maybe by static from a poorly grounded coin door. This CPU problem did not show itself immediately, and let the MPU board function for the most part. The non-functioning reset switch was the give-away here, since this switch connects to the NMI circuit on the CPU chip.
• "My Baby Pacman's playfield GI {General Illumination} lights do not come on when the pinball mode starts, why?"
  The playfield GI lamps are controlled by a Triac, so the lamps can be switched on and off (as the game moves from video to pinball and back to video modes). There is a small driver board which holds the Triac. This board is connected to a switched lamp SCR on the lamp driver board. If all the switched lamps do not work (fuse?), or the SCR on the lamp driver board has failed, the playfield GI lamps will never turn on.