Bally/Stern

Note: This page is a work in progress. Please help get it to a completed state by adding any useful information to it.

1 Introduction

Put system info here

Bally -35 Board Set

Stern M-200 Board Set

Bally Goldball special driver/voltage board

2 Games

A list of solid state games by system and manufacturer (including those that aren't necessarily pinball). Source: http://www.ipdb.org

2.1 Bally

Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Freedom	AS2517-17	AS2518-18	AS-2518-14	Chimes
Night Rider	AS2517-17	AS2518-18	AS-2518-14	Chimes
Black Jack	AS2517-17	AS2518-18	AS-2518-14	Chimes
Evel Kenievel	AS2517-17	AS2518-18	AS-2518-14	Chimes
Eight Ball	AS2517-17	AS2518-18	AS-2518-14	Chimes
Power Play	AS2517-17	AS2518-18	AS-2518-14	Chimes
Mata Hari	AS2517-17	AS2518-18	AS-2518-23	Chimes
Strikes & Spares	AS2517-17	AS2518-18	AS-2518-23	Chimes
Black Jack	AS2517-17	AS2518-18	AS-2518-23	Chimes
Lost World	AS2517-35	AS2518-18	AS-2518-23	AS2518-32
The Six Million Dollar Man	AS2517-35	AS2518-18	AS-2518-23	AS2518-32
Playboy	AS2517-35	AS2518-18	AS-2518-23	AS2518-32
Voltan	AS2517-35	AS2518-18	AS-2518-23	AS2518-32
SuperSonic	AS2517-35	AS2518-18	AS-2518-23	AS2518-32
Star Trek	AS2517-35	AS2518-18	AS-2518-23	AS2518-50
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Paragon	AS2517-35	AS2518-18	AS-2518-23	AS2518-50
Harlem Globetrotters	AS2517-35	AS2518-18	AS-2518-23	AS2518-50
Dolly Parton	AS2517-35	AS2518-18	AS-2518-23	AS2518-50
Kiss	AS2517-35	AS2518-49	AS-2518-23	AS2518-50	Auxiliary Lamp Driver AS-2518-43
Future Spa	AS2517-35	AS2518-49	AS-2518-23	AS2518-50	Auxiliary Lamp Driver AS-2518-43
Space Invaders	AS2517-35	AS2518-49	AS-2518-23	AS2518-51	Auxiliary Lamp Driver AS-2518-52
Nitro Groundshaker	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Silverball Mania	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Rolling Stones	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Mystic	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Hotdoggin	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Viking	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Skateball	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Frontier	AS2517-35	AS2518-18	AS-2518-23	AS2518-51
Xenon	AS2517-35	AS2518-54	AS-2518-23	AS-2518-56	Auxiliary Lamp Driver AS-2518-52, Volcalizer module AS-2518-58
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Flash Gordon	AS2517-35	AS2518-54	AS-2518-23	AS2518-61
Eight Ball Deluxe	AS2517-35	AS2518-54	AS-2518-23	AS2518-61
Fireball II	AS2517-35	AS2518-54	AS-2518-23	AS2518-61
Embryon	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Fathom	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Medusa	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Centaur	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61	Reverb AS2518-81
Elektra	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Spectrum	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Speakeasy	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-51
Rapid Fire	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Granny and the Gators	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot AS-2518-121
Mr. & Mrs. Pacman	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Baby Pac-Man	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot AS-2518-121
Eight Ball Deluxe Limited Edition	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
BMX	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-51
Centaur II	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61	Reverb AS2518-81
Goldball	AS-2517-35	AS-2518-54	AS-2518-147 (combo lamp and solenoid driver)	AS-2518-51
X's & O's	AS-2517-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Kings of Steel	AS-2517-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Black Pyramid	AS-2517-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Eight Ball Deluxe Classic	AS-2517-35	AS-2518-54	AS-2518-23	AS-2518-61
Fireball Classic	AS-2517-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Cybernaut	AS-2517-35	AS-2518-54	AS-2518-23	M-051-00114-B045

2.2 Stern

Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Pinball	M-100			Chimes
Stingray	M-100			Chimes
Stars	M-100			Chimes
Memory Lane	M-100			Chimes
Lectronamo	M-100			SB-100
WildFyre	M-100			SB-100
Nugent	M-100			SB-100
Dracula	M-100			SB-100
Trident	M-100			SB-100
Hot Hand	M-100			SB-100
Magic	M-100			SB-100
Cosmic Princess	M-100			SB-100
Meteor	M-200			SB-300
Galaxy	M-200			SB-300
Ali	M-200			SB-300
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Big Game	M-200			SB-300
Seawitch	M-200			SB-300
Cheetah	M-200			SB-300
Quicksilver	M-200			SB-300
Stargazer	M-200			SB-300
Nineball	M-200			SB-300
Iron Maiden	M-200			SB-300
Viper	M-200			SB-300
Dragonfist	M-200			SB-300
Cue	M-200			SB-300
Flight 2000	M-200			SB-300	Voice module VS-100
Free Fall	M-200			SB-300	Voice module VS-100
Lightning	M-200			SB-300	Voice module VS-100
Split Second	M-200			SB-300	Voice module VS-100
Catacomb	M-200			SB-300	Voice module VS-100
Orbitor One	M-200			SB-300	Voice module VS-100

3 Technical Info

3.1 Attract Mode Test Points

3.1.1 MPU Test Point Values

Model	TP1	TP2	TP3	TP4	TP5
AS-2518-17	+5 +/-.25VDC	+11.9 +/- 1.40VDC	+21.5 +/- 2.7VDC	GND	+5 +/-.25VDC
AS-2518-35	+5 +/-.25VDC	+11.9 +/- 1.40VDC	+21.5 +/- 2.7VDC	GND	+5 +/-.25VDC
AS-2518-133	+5 +/-.25VDC	+11.9 +/- 1.40VDC		GND	+5 +/-.25VDC

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.1.2 Power Supply Test Point Values

Model	TP1	TP2	TP3	TP4	TP5
AS-2518-18	+5.4 +/-.8VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC	7.3 +/-.9VAC	+43 +/-5.4VDC
AS-2518-49	+5.4 +/-.8VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC	7.3 +/-.9VAC	+43 +/-5.4VDC
AS-2518-54
AS-2518-132

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.1.3 Lamp Driver Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5
AS-2518-14	Lamp Driver	+5 +/-.25VDC	GND
AS-2518-23	Lamp Driver	+5 +/-.25VDC	GND
AS-2518-43	Aux Lamp Driver	+5 +/-.25VDC	GND
AS-2518-52	Aux Lamp Driver	+5 +/-.25VDC	GND

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.1.4 Solenoid Driver Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5
AS-2518-16	Solenoid Driver	+5 +/-.25VDC	+190 +/-5VDC	+5 +/-.25VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC
AS-2518-22	Solenoid Driver	+5 +/-.25VDC	+190 +/-5VDC	+5 +/-.25VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC
AS-2518-107	Combo Lamp/Solenoid Driver

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.1.5 Sound Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5	TP6	TP7	TP8	TP9	TP10	TP11	TP12	TP13
AS-2518-32	Sound	+5 +/-.25VDC	GND	+12.5 +/-1.3VDC	+43 +/-5.4VDC	SOL RET	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-50	Sound
AS-2518-51	Sound	+11.9 +/- 2.5VDC	+5 +/-.25VDC		0VDC (No Sound), 2.5+/-.2VDC (Sound)	+2.5 +/-.2VDC	0VAC (No Sound), .35 +/-.1VAC (Sound)	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-56	Sound	+11.9 +/- 2.5VDC	+5 +/-.25VDC	GND	0VDC (No Sound), 2.5VDC (Sound)	+2.5 +/-.2VDC	0VAC (No Sound), .35 +/-.1VAC (Sound)	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-57	Vocalizer	GND	+5 +/-.25VDC	Analog Output	Digital Input	Speech Clock	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-61	Sound	GND	+5 +/-.25VDC	+11.5VDC	-5VDC	Speech Volume Control Voltage	Sound Volume Control Voltage	AY3-8912 Output	E	TMS5200 Output	VMA	TMS5200 Clock	Reset
AS-2518-81	Reverb	GND			Audio In							+11.9VDC	+12VDC	+4VDC to +8VDC
M-051-00114-B045	Sound

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.1.6 Display Module Test Point Values

Model	Board Type	TP1	TP2	TP3
AS-2518-15	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-21	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-58	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-121	Vidiot

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.2 Fuse Values

Model	Board Type	F1	F2	F3	F4	F5	F6
AS-2518-18	Power Supply	10A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	3A, 32V 3AG SB
AS-2518-22	Solenoid Driver	1/4A, 250V 8AG	N/A	N/A	N/A	N/A	N/A
AS-2518-49	Power Supply	20A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	N/A
AS-2518-54	Power Supply	20A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	N/A
AS-2518-107	Combo Lamp/Solenoid Driver
AS-2518-132	Power Supply

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

Unless noted otherwise, all fuses are fast blow

3.3 Jumper Info

2x2732:

Bally -35 4-13a, 7-8, 10-11, 12-Ground, 16a-29, 31-32, 33-35

Stern MPU-200 1-2, 4-5, 13-15, 16-18, 24-25, 32-33, 34-35

3.4 Bally/Stern MPU Board LED Locked On/Never Lights

If the LED never lights, either the +12v (TP2, J4 pin 12) is missing or the LED is bad. By default, the LED is ON until the software tells U11 to turn it OFF.

If the LED lights solid, there's some more digging to do. First off, if the board has any corrosion damage at all, it needs to be cleaned and neutralized before attempting any repairs; while shot-gunning components might fix the board, it won't be 100% reliable if the corrosion isn't addressed.

Next, put your DMM or a logic probe on pin 40 of the 6800 cpu chip (U9). Power on the board - you should see the voltage remain low/at zero and then approx 1/10 of a second later, rise to about +5 vdc (high). This is the reset signal, sent from the components in the lower left corner of the board throughout the board to U9, U10, and U11. What the reset section (called the 'valid power detector') does is not allow the mpu to boot until the +12 volts are stable over the value of ZR1 (a zener diode, usually either 8.2 or 9.1 volts). This delay ensures that the +5 voltage is stable enough to run the mpu board reliably (the +5 volts is derived from the +12 volts on the solenoid driver/power regulator board).

The 6800 cpu chip will not 'unlock' and start program execution until it sees a transition from a low (0 volts) to high (~5 volts) signal. This is the purpose of the power on reset delay. The reset delay and signal must be present at all 3 U9, U10, and U11's reset inputs (pin 40 on U9, and pin 34 on U10/U11). If the signal starts out immediately at a high level, the mpu will not start to boot until the transition takes place. If you have a locked on mpu you can take a screwdriver or your meter probe and short pins 39 and 40 together for a brief moment on U9; if the game starts to boot after doing this, it's a safe assumption that the reset circuit is to blame. (Shorting the pins together simulates what the reset circuit does).

If you need to rebuild the reset circuit, full kits are available from specialty suppliers such as Great Plains Electronics or Big Daddy Enterprises to replace all the components in the corrosion zone. Bare bones to replace are Q1 (2n3904 or 2n4401) and Q5 (2n4403 or 2n3906) but it is a good idea to go ahead and replace all the parts that come in the kit; do so one at a time to ensure that you do not mix any up. Note there are a some components that are polarized in their installation - VR1, CR5, Q1, and Q5. Look carefully at the board to see if there are traces on the top and bottom of a component; it is recommended to solder these from the top and bottom of the board to ensure that a good connection is maintained.

The following is the list of parts for the reset section that should be replaced. Parts listed with more than one type are equivalent and can be substituted freely. It is also possible that the inductors L1 and L2 need to be replaced as well, however this is very rare. If there is heavy corrosion on them they should be replaced.

Transistors:

Q1 2N3904/2N4401 (lower left area)

Q2 2N3904/2N4401 (near LED)

Q5 2N3906/2N4403 (lower left area)

Diodes:

VR1 zener 1N9598/1N4738A

CR44 1N4004 rectifier diode

CR5, CR7 1N4148 switching diode

CR8 LED

Capacitors:

C1, C2 820pF ceramic capacitor

C3 0.01uF ceramic capacitor

C5 4.7uF tantalum capacitor

C13, C80 0.01uF ceramic capacitor

Resistors: (1/4 w unless noted)

R1, R3, R24, R28 8.2k

R2 120k

R11 82 ohm/2 watt

R12 270 ohm

R16 2k

R16 2.2k (stern mpu-200 only)

R17 150k

R29 470 ohm

R107 3.3k

R112 1k

R134 4.7k

R140 20k

If your reset circuit is operating as designed yet the LED is still locked on, next step is to pull all the chips from the board except for U9, U11, and U6 (leave all chips U1-U6 installed on Stern MPU boards. Only U6 is required on Bally boards to perform the initial LED turn off). It helps to have a known working U6 from a bally game to use as a test chip for this purpose. Be aware that you need to know/have the board jumpered for the correct type of chip you're inserting.

See if the board boots with just the chips above installed - if it does, add these chips back in this order to see which might be bad: U10 PIA, U1-U5 program chips, U7 6810 ram, U8 5101 ram. Often a bad ram/rom can cause the entire system to lock up. Bad chip sockets can be a factor as well; the early Bally -17 boards have a closed type brown socket that's especially prone to failure.

Double check the jumpers to ensure they match the rom chips you have available, and change the rom chips to known working ones for testing. A final thing to check if the machine won't boot is the clock circuit; it is fairly robust and it is far more common that the reset circuit itself or chip sockets are the issue. To check the clock circuit you need a logic probe or oscilloscope. A multimeter might show the average voltage on a clock circuit, or it might just show meaningless constantly changing numbers. The clock signal is pin 3 on the cpu chip, and the shifted clock signal goes to pins 36 and 37. The frequency is about 500 kilohertz for Bally -17, -35 and Stern MPU-100 boards, and approximately 850 kilohertz for the Stern MPU-200 board.

If the clock signal is missing, pull U9 first to make sure the CPU chip isn't damaged and test it again.

It can be frustrating to track down a locked on LED problem, but breaking the problem up and testing each section individually helps. Just remember that if the LED turns on and then off, most of the battle is won. The board has booted far enough that the software was able to start and turn off the LED. Proceed onto the LED flash testing to determine what needs to be fixed beyond that.

---

3.5 Bally/Stern MPU Board LED Flash Sequence

Bally and stern boards on startup have an LED that flashes to tell you the results of tests of various parts of their system. This section explains what is being tested and how, according to information from the Bally "FO-561-2 Theory of Operation rev. 5-1982" manual, and the Stern manual "Theory of Operation, Stern's Microprocessor Controlled Solid-State Games".

When power is first applied to the mpu board, the led by default is ON. The very first set of valid instructions in every bally/stern game is to turn the led off. This is more of a flicker than a flash, so is not counted as a flash in the 7 flash sequence.

3.5.1 Quick summary

Flicker: MPU reset good, program booted.
1st Flash: ROM Checksums OK
2nd Flash: U7 6810 ram OK
3rd Flash: U8 5101 ram OK (U8 & U13 on mpu-200)
4th Flash: U10 PIA OK (see details for caveats)
5th Flash: U11 PIA OK (see details for caveats)
6th Flash: U12 555 Display interrupt timer OK
7th Flash: Zero crossing interrupt detector OK (solenoid voltage present)

3.5.2 First flash:

After the program is running (led flicker tells you the cpu chip was able to start a valid program stored in the eproms) the program performs a checksum of all program chips u1-u6. Most Bally games' programming is split between an operating system chip U6 and a game rom chip U2; Stern's games were a little looser - the operating system and game code are freely interspersed.

Bally checksums are calculated by summing each byte, discarding any carries. Most games check their code in $0400 blocks, so it would be possible to determine down to the chip which chip failed this checksum. (A 2716/9316 chip has hex $0800 space available in it - 2732 sized images are $1000 in size. The smallest chip used was a 474 PROM which has $0200 bytes available) However, to do so would require a way to read the X register from the 6800 cpu chip at the time of checksum failure, so if you do not get the first flash, it is best to replace the U6 chip first, then move onto the other chips U5, U2, and U1 (if present).

Stern checksums are calculated similarly, but not in chunks - the entire program space is summed and must equal $00 for the first flash to occur.

Regardless of the manufacturer being Bally or Stern, after the checksum is passed, the first flash occurs.

3.5.3 Second flash:

Next, the program tests the 6810 RAM chip at U7, by writing the data $00 to each memory location contained in the ram ($00-$7F). It then reads back each location to ensure that $00 is returned. It increments the data to $01 and repeats this test; this continues until the data read back is $FF (256), the maximum value any one byte can store in the RAM. It then increments the memory location being tested, and repeats the $00-$FF data storage test. If any of the tested locations returns an unexpected result, the program stops, alerting you to a problem with U7 (since you got the first rom checksum flash, but not the 2nd U7 OK flash)

3.5.4 Third flash:

Now, the program tests the 5101 Non-volatile RAM chip at U8 (U8 AND U13 on Stern mpu-200 boards). The 5101 stores bookkeeping data, game parameters, high scores, replay levels, etc. The program tests this ram ($200-$2FF) by reading the original nibble/byte (see sidebar) and saving it in a temporary location, then storing a test pattern in the location similar to the U7 test. After the byte successfully passes the test, the original data is returned to the location, and the program loops onto the next byte.

LEARN MORE: How does a 128 byte 5101 RAM occupy 256 memory locations?

If you look at a pinout of the 5101 memory, you will notice it is a 128 byte device. Yet, it is addressed by the mpu via 256 memory locations ($200-$2FF). This is because the 5101 is actually a 256 nibble device - a nibble is a half-byte (4 bits). So data stored to a 5101 in a pinball machine actually only stores half of the data byte being sent to it. Which half depends on the board design - Bally and Stern use the upper nibble for storage, and Williams used the lower nibble. Stern mpu-200 boards have an additional 5101 at U13 - this stores the lower nibble in conjunction with U8 storing the upper nibble of a byte saved to $200-$2FF, allowing mpu-200 games to store more data and avoid doing some fancy processing in getting the data in and out of the non-volatile ram area.

For example, here's some pseudo-machine code for what happens: LOAD #$24 (the data you want to store is 24); STORE $231 (you want to store the data 24 at memory location $231); READ $231 (you want to read back the data you just stored). The data returned is not #$24 as expected, but rather #$2F. The lower nibble was never stored, as the 5101 memory does not store data as bytes but rather as nibbles. To store #$24 properly would require splitting the byte into its nibbles '2' and '4', storing the 2 in one memory location, doing some shifting to the 4, and storing it in another memory location.

Showing the byte as binary might be helpful to visualize what's involved. The hex #$24 in binary is %00100100 - split into nibbles is %0010 (the 2) and %0100 (the 4). The upper nibble is the one the 5101 is able to store directly, but the position in the byte of the lower nibble prevents it from being stored. A shift operation is performed 4 times on the byte to reposition the lower nibble as the upper nibble, enabling it to be stored to the 5101. (Each shift moves the binary pattern to the left one bit - here's the full sequence: Start=%00100100, shift left=%0100100x, shift left=%100100xx, shift left=%00100xxx, shift left=%0100xxxx, giving you the #$4 in the high nibble) All byte data has to be split this way to be saved, and recombined on reading from the single 5101 ram boards (bally -17 and -35, stern mpu-100). You can see why Stern added the second 5101 ram to their boards, to make programming much easier!

3.5.5 Fourth and Fifth flashes:

Next, the program tests each of the 2 6820/6821 PIA's (peripheral interface adapters) at U10 and U11, starting with U10. The PIAs are set to a known state, then data is stored and read back from them to verify their registers are functioning properly. It is important to note that it is not possible for the PIA to be 100% tested with this test as external data would have to be fed in to do so, but the test will at least test the internal registers. (So it would be possible for a PIA to pass the self-test, but still not work properly with external inputs)

Assuming the PIAs pass, the fourth (U10) and fifth (U11) LED flashes occur. (The LED itself is connected to the U11 PIA - so if the LED is locked on, U11 might be bad. It's worth letting a locked on LED board 'sit' for a minute or so to see if the game boots all the way up without flashing each test step. This is an example of how a PIA can pass self test but still be bad, as the LED control pin has no feedback as to if the LED is in fact flashing)

3.5.6 Sixth flash:

The sixth flash waits for an external input on U11 pin 40 from the display interrupt generator circuit - this occurs 320 times a second. If you're missing the sixth flash, there may be a problem with either the U12 circuit, OR the input pin on the PIA. A logic probe, oscilloscope, or a multimeter on pin 40 can help you determine which. A logic probe will pulse if the display circuit is operating, the scope will show you the signal's waveform, and the multimeter should settle on a voltage somewhat between 0-5 volts. With no sixth flash but good results from the measurement, it's a safe bet that U11 is bad and needs to be replaced.

Note that the sixth flash does NOT check for the proper frequency of operation of the display generation circuitry. As long as there is a pulsing signal (technically, ONE state change), the test is marked good and the program allowed to continue.

3.5.7 Seventh flash:

The last flash waits for an external input on U10 pin 18 from the zero crossing detector circuit - this occurs 120 times a second (as the AC waveform passes or "crosses" 0 volts). Diagnosis of issues with the 7th flash are similar to the 6th flash; you can measure the input to pin 18 to determine if the signal is present or not. Signal present but no flash could mean a bad U10 PIA. Signal missing usually points to missing solenoid voltage (the source of the zero crossing signal is derived from this voltage delivered from the rectifier board) or if present, an issue with the zero crossing detection circuit itself.

Note again that the seventh flash does NOT check for the proper frequency from the zero crossing detector, it simply checks for a pulsing signal, and it only checks for ONE transition.

After the 7th flash, the program does some background setup, reads dip switches, enables the displays, attract modes, switch scanning etc. in a 'game over' mode, waiting for player input. The LED will sometimes be dimly glowing or even pulse as this happens, which is not a cause for alarm - you can rebuild the LED circuit around Q2 if this worries you, but it is harmless.

3.6 The Single Largest Culprit in MPU death

---

By far the largest reason the MPU board stops working is because of alkaline corrosion from the on-board rechargeable batteries. The original battery used on the board is a 3.6 volt nickel cadmium rechargeable battery; over time, this type of battery leaks corrosion into the traces surrounding it, affecting the 5101 memory, the reset circuit, the 6810 memory, the LED area, and all the traces around it. One of the worst boards had corrosion stretching throughout the entire ground plane of the board.

If you have a battery on the board, it is recommended to remove it immediately. There are several different ways to replace the battery; in order of preference: 5101 ram eliminator, memory capacitor, nothing, lithium battery, remote mounted AA battery pack, exact replacement. Let's look at each of the options in turn and weigh their pros and cons.

5101 Ram Eliminator

A 5101 ram eliminator doesn't eliminate the ram per se; it replaces it with a more modern ram that is either flash ram or has an internal battery built into it.

Advantages: eliminating a static sensitive obsolete part, eliminating any type of battery that could leak, high reliability, very long retention time (10-99 years)

Disadvantages: relatively high cost, need to remove the 5101 (if not socketed) and replace or add a socket, stressing relatively frail mpu board traces, flash ram type can wear out (although unlikely)

Memory Capacitor

A small capacitor (5.5 volt 1.5 farad works well) is added to the board in place of the original battery. The charging circuit for the rechargeable battery works just fine in maintaining enough of a voltage to enable the capacitor to act in place of the battery.

Advantages: relatively low cost, easy installation, no risk of battery leakage, high reliability

Disadvantages: large initial charge time, some 5101s draw too much current, must turn machine on every couple of months to top off capacitor

Nothing

Removing the battery and cleaning the board up, you do have the option to replace the battery with nothing. If you don't care about audits, settings, or high scores, this is a valid option. Some software might not like having random garbage in its memory range, though. If you have a stern mpu-200 based game, do not leave the battery out as the random garbage will cause problems with stern's software.

Advantages: No risk of leakage, ever

Disadvantages: No high scores save, no audits, garbage in ram can cause issues with some software

Lithium Battery

Replacing the original nickel cadmium battery with a lithium battery is possible; however it is imperative that you add a blocking diode to prevent the battery from being charged.

Advantages: Very long life (10 years on average), cheap, can be mounted far from boards so any leakage would not leak onto boards

Disadvantages: Must use blocking diode, can leak (unlikely), any leakage difficult to clean up

Remote Mounted AA Battery Pack

A popular and inexpensive option is to replace the original battery with a small AA pack, with a blocking diode. Like the lithium replacement option, it is essential to have a blocking diode (usually incorporated into the pack) so the mpu doesn't try and charge the AA batteries. If you get lithium AA batteries you can get very long life. This type of battery pack needs to be checked periodically to ensure no leakage is occurring.

Advantages: Low cost, can be moved far from boards so if batteries so leak they do not leak directly onto boards

Disadvantages: Periodic maintenance (replacing/checking), can leak

Exact Replacement

You can replace the NiCad with a NiCad. Not recommended as all of the original pitfalls of the original battery are still present, but it will work. Many people use cordless phone batteries to do this; just make sure the voltage and amp hour rating are similar to the original battery. (3.6 volt 150 milliamp hours)

Advantages: Low cost, can also be mounted far from boards so any leakage does not leak directly onto boards

Disadvantages: Can leak, needs periodic maintenance (checking for corrosion)

Note that all of the replacement options that include batteries are subject to the same conditions causing leakage as the original battery was. It is strongly recommended that if you decide to use a solution that uses a battery as its power source to remotely mount the battery so that any future leakage does not drip onto the boards. The bottom of the head is a good choice as is the sidewall in cases where there are no boards mounted there. Corrosion can and does travel through the wiring used to relocate the batteries however, so periodic inspection of the batteries and board are necessary to ensure that no further corrosion is occurring.

3.7 Installation of Various Battery Eliminators

---

AA Battery pack

Memory Capacitor

Remove original battery, neutralize and clean any corrosion left behind/inspect parts in area, replace as needed. Drill a small hole to the left of the original batteries' negative terminal. Install the capacitor with the negative lead in the leftmost hole of the negative terminal, soldering it into place. Solder a lead to the positive terminal of the capacitor and bend the leg over to help hold it in place. Solder the other end of the lead to either the positive hole from the original battery, or to the bottom lead of R12. Double check your work in reference to the negative lead of the capacitor. Turn the machine on an let the capacitor charge for between 8-12 hours. Once the cap is charged, turning the machine on for about an hour a month will keep it topped up.

Original style battery, cordless phone battery

Remove original battery, neutralize and clean any corrosion left behind/inspect parts in area, replace as needed. Solder new battery in, or better yet, attach fly leads to battery and remote mount. Turn machine on for large initial charge to battery.

3.8 Bally Solenoid Driver for Dummies

First off, take a look at the picture below:

This is a typical Bally coil from a Mata Hari machine. Notice 3 things: The two big fat yellow wires going to one lug, the small skinny wire going to the other lug, and the diode connected to the two lugs.

One lug on every coil is visited by these fat wires, in what's called a daisy-chain. This is the wire that supplies each coil with positive 43 volts DC (+43VDC). So each coil is connected to the +43VDC bus. Most have two fat wires, but some may have one. Flipper coils have these wires too, but they are connected a little differently, and are discussed elsewhere. For now, just assume we're talking about regular solenoids here.

Next, you'll notice each coil has a small skinny wire on the other lug. This wire goes to the control circuits on the solenoid/regulator board. In order to energize the coil, there must be a path to ground for the +43VDC. Normally, there is not so the coil is relaxed. When the small skinny wire gets connected to ground, the path is complete and current will flow. This current flow turns the coil into an electro-magnet and then pulls the plunger into the coil. When the wire is disconnected from ground, current flow stops, the electro-magnet is turned off, and the plunger returns to it's normal position, with help from either a spring, or gravity.

Finally, the diode. When the current is quickly turned off on an energized coil, the magnetic field around the coil collapses quickly and causes the coil to generate a huge voltage spike. The job of this diode is to prevent the majority of this spike from reaching the solenoid driver circuity. If the diode is bad, or installed backwards, you'll pop the driver transistor the first time the coil is energized, then released. It's like the ignition in older cars - when the points open, the 12 volts is removed from the car's coil quickly, which causes another coil to generate a huge voltage spike, to the spark plug. The computer program that runs the machine also tries to limit this spike by turning off the coil near the zero crossing of the line AC. This helps because the DC that drives the coils is rectified, but not filtered, so it's not smooth DC, but "humpy", like in this picture:

By energizing the coils just after the zero crossing, the in-rush of current caused by a coil is limited, and by turning them off just after the zero crossing, the voltage spike caused by the collapsing field is also kept to a minimum.

So, in the simplest form, the solenoid driver circuits in your Bally look like this:

Look at it as a bunch of coils all connected to the +43VDC bus, and the other lugs going to switches which are also connected to ground. Then, if you were to close a switch, that would connect the circuit from +43VDC to ground, and the coil would energize as long as the switch is closed.

Now see how the circuit is complete due to the switch being closed, and the coil is energized. Then you open the switch and the coil turns off and you're back to the first picture. If the diode were not there, when you opened the switch, there's be a big arc across the switch contacts at the moment they opened up.

Finally, take this one step further and replace the manual switches with transistors. Transistors are normally used as amplifiers, but you can also use them as switches too. There are 3 leads on a transistor, the base, the emitter, and the collector. For NPN transistors like the ones on your Bally solenoid driver, you can used the emitter and collector like a switch. With no current supplied to the base, there is no current flow between the collector and emitter, so the transistor switch is open, or OFF. If you supply a current to the base, current will then flow between the collector and emitter, so now the switch is closed, or ON.

Without getting into too much detail - what happens is a current is applied to the base which is high enough to 'saturate' the transistor. This means the collector-to-emitter current will be amplified as high as it can, and the transistor will then conduct a large amount of current from COLLECTOR to EMITTER, in relation to the current flow from the BASE to the EMITTER. This is how it acts like a switch. The base goes high to turn it on, and low to turn it off. Since the collector is connected to the wire that goes to the coil (the small single wire), and the emitter is connected to ground, turning the transistor as the effect of connecting the collector to ground. This completes the circuit to the coil and it fires.

You may have heard that you can test a coil by grounding the tab on the coil's driver transistor. For the TIP-102 transistors used in the Bally solenoid driver, the metal tab is connected to the collector. Knowing this, and what you've just learned, you can now see that grounding the tab is the same as grounding the collector, which will complete the circuit to ground and fire the coil. Note that this test only tests the wiring from the solenoid driver to the coil. It DOES NOT test the transistor, or any circuitry before the transistor.

So, you can now replace the transistor and "control signal" in the simplified drawing above, with the actual circuit and more details found in the following section.

--Stevekulpa 21:06, 22 April 2011 (BST)

3.9 Bally Solenoid Driver

Bally AS-2518-16 Solenoid Driver/Regulator

Bally AS-2518-22 Solenoid Driver/Regulator

Stern SDU-100 Solenoid Driver/Regulator

Another style of the Stern SDU-100 Solenoid Driver/Regulator

First off, everything mentioned on this page is in reference to the Bally AS-2518-22 model solenoid driver board, found in most Bally pins from 1977 through 1985. Since it is very similar to the AS-2518-16 board and is identical as far as the operation of the solenoid driver circuits, you can assume it is applicable for these boards as well.

Second, if all this is Greek to you and you have no idea how Decoder ICs work, or what a Transistor is, take a look at the Bally Solenoid Driver for Dummies article above first to learn the basics of how this stuff works.

Thirdly, this model of solenoid driver board actually has three functions: The first obviously is to drive the solenoid and relay coils of your pin, the second is a 5-volt regulator which provides a nice and steady 5 VDC to the other boards for their various logic circuits, and third is the high voltage regulator (190 VDC) for the display driver boards. I won't be discussing the voltage regulator stuff here, just the solenoid driver parts.

Finally, Don't forget that the Solenoid Driver board contains the high voltage circuitry for the displays. There is 190 volts DC here and if you're not careful, you'll get knocked on your ass. A shock from 190 volts DC will hurt. If you don't know what you're doing, then keep away from it and have a professional fix it instead. In addition to high voltages, there are static sensitive parts on this board, so if you're going to work on it, be sure to properly ground yourself before touching the board, and always work in a static-free workspace.

3.9.1 Overview

We'll be discussing things from two circuit boards: The MPU board (AS-2517-17 or -35) and the Solenoid Driver board (AS-2518-22 or -16). The solenoid driver gets signals from the MPU board. These signals tell the solenoid driver which solenoid to fire. Up to 15 momentary and 4 continuous solenoids can be controlled by the solenoid driver. The flipper solenoids are enabled or disabled from the solenoid driver too, but are not controlled like the other solenoids.

3.9.2 How the Solenoid Driver Works

The solenoid driver is responsible for energizing the solenoid coils of your pinball machine. Four signals from the U11 PIA integrated circuit on the MPU board travel out from the J4 to the J4 connector on the Solenoid Driver board. These four signals tell the Solenoid Driver which solenoid to fire. This is accomplished by using a decoder chip that takes the binary pattern of the four signals (16 different patterns) and decodes (or demultiplexes) them into one of sixteen different outputs. The four signals are applied to the decoder then the decoder is strobed. Normally, all sixteen of the decoder output lines are held high (+5 vdc). When strobed, the decoder lowers one of it's sixteen output lines, depending on the pattern of the four input signals. You can learn more about the 74LS154 decoder chip from here.

Take a look at the schematic below, which shows one typical output line and the associated circuitry to drive a single solenoid coil:

With no input supplied (strobe is high), the output lines of the decoder are high (+5 vdc). This puts a voltage at the base of Q1 (this transistor is one of 7 in the CA3081 chip). This turns Q1 "on" and the voltage supplied to it's collector via resistor R1 passes through the transistor to ground. At this point, little or no voltage is present at the base of Q2, and Q2 is "off". With Q2 off, the 40 vdc at the coil has no place to go, and the coil remains deenergized.

When the MPU board supplies the proper input signals (A-B-C-D) to the decoder, and the decoder is strobed (signal drops to low), the proper output signal will go low, which turns Q1 "off" (notice one of the two strobe lines goes to ground, so it's always low). This allows the +5 vdc at Q1's collector to flow through the diode instead of Q1 on it's way to ground via resistor R3. This also puts a voltage at the base of Q2 and turns this transistor "on". When Q2 turns on, the 40 vdc at the solenoid now has a path to ground through Q1 and current flows through the coil, thereby energizing it. Then the strobe to the decoder is released, the decoder output goes high again, Q1 turns on, Q2 turns off, and everything is back to normal.

Diode D1, resistor R3 and capacitor C1 work to slow the speed at which Q2 and the solenoid are able to turn off. This is important to prevent the "inductive kick" voltage that builds up when you try to turn off a solenoid quickly. A solenoid coil can build up hundreds of volts if it is switched off too quickly. For example, the spark in the spark plug of a car is generated from this inductive kick when the ignition coil is turned off quickly. In this case, D1 allows Q2 and the solenoid to turn ON quickly (which is OK) because the current that used to be flowing through Q1 can now flow forward through D1 and turn on Q2 quickly. However, when the decoder output goes back to high and Q1 turns back on, D1 prevents the charge from the base of Q2 from being sucked down Q1. The charge on C1 must drain off (slowly) through R3 and the base of Q2. This takes awhile and slows the turn-off of Q2 and the solenoid COIL, thus reducing the kick. Also, as the solenoid turns off and the voltage on the collector of Q2 starts to rise, this voltage is "fed back" by C1 to the base of Q2 and tends to keep Q2 on a little longer, slowing the turn-off of the solenoid even more. The OTHER diode (D2, across the solenoid) works to absorb the solenoid's turn-off kick by conducting when the voltage on the collector of Q2 is greater than about 40 volts.

--Stevekulpa 21:07, 22 April 2011 (BST)

3.9.3 Testing and Replacing Transistors

To test a transistor set you DMM to diode test mode. With the game turned off place the black lead on the metal tab of the transistor. Probe the two outer legs of the transistor with your red lead and the DMM should read between .4v and .6v (some DMM will show 4xx - 6xx). The center leg should be a dead short to the metal tab. If either outer leg reads anything but .4v to .6v then that transistor needs to be replaced. Use TIP-102 as the replacement transistor.

If a transistor needs to be replaced it is usually a good idea to check / replace the 1n4004 diode and 330 ohm resistor associated with that transistor as these will often burn / short. Also check the diode on the associated coil, it is likely to be shorted as well.

--barakandl 15:15, 1 May 2011 (EST)

3.9.4 Solenoid Driver Upgrades

There are some upgrades that you can do to reduce stress on connectors.

There are two 5v test points on the SDB and these can be tied together. On the solder side of the driver board jump TP1 and TP3 together. Be careful you get the right test point. This reduces stress on connectors.

Next the C23 cap needs a common ground with the rest of the SDB. Jump the negative side of C23 to a convenient ground trace. Most boards there is a ground trace going right by the C23 negative lead, other boards might require a longer jumper.

C26 needs a similar upgrade that C23 got. Tie the negative side of C26 to the ground trace going along the outside of the board. This connects both C23's and C26's negative side to a common ground on the SDB reducing stress on connectors.

See this picture for a visual description of the upgrades.

--barakandl 20:30, 26 April 2011 (EST)

3.9.5 How to Rebuild the Bally/Stern Solenoid Driver Board

The Solenoid Driver board is critical to the operation of the electronics of the game. The Solenoid Driver Board (SDB) comes in several types for Bally and Stern, and are completely interchangeable for any game of the 6800 MPU type. The SDB supplies the game with the voltages for the MPU, coils and high voltage for the displays. Recommendations are given below for replacing components to ensure proper operation and reliability. In all cases, do the ground modifications as shown in another part of this Wiki.

Minimum Recommendation for a Working board

At a minimum, replace both large capacitors on a working or non-working board, especially if they look original. Original caps are often metallic blue or metallic silver, and are at least 30 years old and due to fail, owing to the electrolytic chemicals in the capacitor drying up. The capacitor at C 23 has a factory value of 11,000 uf and 20 volts, but these values are not easily found these days. A electrolytic capacitor of between 11,000uf and 16,000 uf and 25 volts or greater can be safely substituted. A screw terminal capacitor makes for a easy installation, but a snap cap with leads can be used as well. Recent prices for screw terminal caps have increased greatly so this may be a factor in your decision.

The high voltage capacitor at C26 has an original spec of 160 uf and 350 volts and is a axial electrolytic capacitor. Once again, this part is difficult to encounter with these exact specs, but a axial or radial cap from 150uf to 180 uf and at least 350 volts can substitute. 400 v or 450v caps can be had in a radial format and size that will fit. With a radial cap you will have to make leads that bend back to the negative (-) solder pad.

Preferred recommendation for a working board

Besides the above, replace ALL the .100 and .156 molex header pins and the connector terminals in the nylon housings with Molex TRIFURCON Phosphor Bronze tin plated crimp terminals (Molex Part# 08-52-0113 for 18-20 ga. Wire, and 08-52-0125 for 22-26 ga.) for the .156 connectors, and Molex .100 tin plated Phosphor Bronze crimp terminals, (Molex Part#08-52-0123). Do NOT skimp on this step and just do one or the other. The receptacles if not burnt, can be re-used. If replacing the receptacles, the locking or non- locking ramp type are fine. Often, the connector at J5 does not cover the last few pins. I don’t like this personally, although no harm can be done IF the key is in place.

Check every resistor that is usually covered by the plastic shield between the two big heat sinks for correct value and no sign of burn. Replace any that are suspect. Use the diode function on your multimeter to check the zener diode at VR1 and the 1N4004 diode. The zener diode can be difficult to source. See below for recommendation.

Gold Standard for Working or NON-WORKING board

It doesn’t make too much sense trying to trace down the exact problem and replacing only the bad components on a NON-WORKING board. Better to replace every possible bad component and start fresh. To ensure long life and proper operation of a working board, in ADDITION TO THE ABOVE, it is recommended that the components below are replaced regardless. Below is a list of components that effect the HV and +5 volt logic circuits on the SDB. Replace them all ! * The Stern Revision J board is rather different, & a component list for that board follows. It can be identified by the extensive silk screening of each component and its function as seen in the 4th photo above, and by the HUGE 2 Watt and (2) large 1 Watt resistors. It is most often found on late date Stern games like Flight 2000 or Viper, etc.

Component replacement list for Bally AS2518-16 or -22 and Stern SDU100 SDBs, except * revision J

Resistors

• R51 22k ohm 1/2Watt
• R52 390 ohm 1/4 Watt
• R54 8.2k ohm 1/4 Watt
• R55 1.2k ohm 1/4 Watt
• R56 82k ohm 1/2 Watt
• R35 100k ohm 1 Watt

Diodes

• CR21 1N4004 400PIV 1 amp or better (1N4007, etc.)
• VR1 Zener diode 1N5275A 140 volts, 1 Watt. Can Sub NTE 5099A

Transistors

• Q21 2N3584 250volts, 2 amp, TO-66 NPN
• Q22&23 2N3440 250 volts 1 amp TO-39 NPN
• Q20 LM323k (original 78H05KC or LAS1405)

Capacitors

• C27&28 .01 uf 400 vdc metal polyester capacitor

• RT1 25k ohm potentiometer (2 types) a 15mm black one, Piher Part# PT15LH06-253A2020 or a 6mm blue one BournsPart#3306P-1-253

Stern SDU100 revision J

• R35 100k ohm 1 Watt
• R51 33k ohm 2 Watt
• R52 390 ohm 1/4 W
• R53 2.4k ohm 1/4 W
• R54 8.2k ohm 1/4 W
• R55 1.2k ohm 1/4 W
• R56 82k ohm 1/2 Watt
• R73 3.3 ohm 1/4 W
• R74 470 ohm 1/4 W
• R75 100k ohm 1 Watt
• CR22 1N4004 or better
• Q24 2N3904 Transistor

Other diodes, transistors and capacitors as above for AS2518-18 --Pinballbob 20:12, 15 May 2011 (BST)

3.10 Bally 6-Digit Displays

This section will help you understand and repair your Bally 6-digit displays. The information is focused on the AS-2518-21 display. Since the AS-2518-15 display is interchangeable with the "-21" display, everything mentioned here will apply to both displays. 7-digit displays behave the same too, so this information will be helpful for those too. The only real difference is an additional digit enable signal, and some more electronics on the board to drive the 7th digit.

If you could care less how they work, but are looking for information on how to repair them, then look for the Repairing Bally Displays article below. We'll also show you some ideas on how to keep your displays working properly.

A healthy Bally 6-Digit Display

Examples off a Bally AS-2518-21 6-digit display, and a Bally AS-258-15 6-digit display:

You can see that the two displays are a little different in the way the components are laid out. Regardless of the differences in appearance, they both perform the same function and are interchangeable with each other The original display (at least the one mentioned in my Power Play Owner's Manual) is the "-21". The two shown here were upgraded with 1/2 watt 100K ohm resistors. A modification that you should do on all your displays too.

Here are some Stern displays that will work in place of the two above:

3.10.1 How the displays work

The way the display circuitry works is really quite interesting. Although the human eye can not detect it, at any given moment, each display is only showing one digit at a time. The program that runs on the machine's computer is changing the digits so fast that you can not tell. If you were to film the displays and play the film back in slow motion, you'd see all the displays showing the same digit, and it cycles through all six, from left to right. It just cycles so fast that your brain thinks the whole display is lit all the time.

As you can see, each display has six digits, and if you look closely, you can see that each digit consists of seven segments. This is important stuff to know in order to understand how these displays work, and most important, how to fix them cheaply!

If you study the display's schematic, you can see that there are 4 main "parts" of a display assembly: The glass display itself, and the display driver consisting of the input decoder, six digit driver circuits, and seven segment driver circuits. There is one digit driver circuit for each of the six digits, and one segment driver circuit for each segment of a digit. How the actual glass display does what it does in order to light various digits and segments is beyond the scope of this tutorial, so we'll ignore that. The decoder takes a number from 0 - 9 as input and determines which segments need to be energized in order to represent this number. The digit drivers are responsible for applying the proper voltages to the proper pins of the display to tell it which digit to light. The segment drivers are responsible for applying the proper voltage to the proper pins of the display to tell it which segments of the digit to light. It is the MPU's job to supply the proper signals to the display driver to make it do all this stuff.

The decoder is a small integrated circuit (MC14543LE) called a "BCD To Seven Segment Decoder". This decoder happens to be a "latching" decoder, which means it latches on to it's inputs and keeps them, even if they are no longer applied, until the decoder is told to release them (blanked). The decoder also has an input called a strobe. When strobed, the decoder will read it's four inputs and latch on to them. A strobe signal is usually a quick off/on/off pulse. There is also an input for the blanking signal.

BCD stands for Binary Coded Decimal and is a fancy term for storing a number from 0 - 9 in a half byte of storage (four bits). Using BDC encoding, each byte of memory can store two digits. Anyway, the input of the decoder is a BCD number from 0 - 9, and the output of the decoder is seven signals. These seven signals are either on or off, and relate to the seven segments of a digit. Each of the seven output signals go to a MPS-A42 transistor, which is part of a circuit called a segment driver. This transistor acts like a switch to turn the segments on or off. The outputs of the seven segment drivers go to the seven segment pins of the display glass. So this is how the computer tells the display driver which segments to light. The MPU has a four-signal data path that goes to all five displays (or seven for Six Million Dollar Man). These four signals provide the 4-bit input into the decoder, and remember, all four signals go to ALL of the displays. Below is a diagram of how the segments are labeled, and a truth table showing the 15 possible inputs and outputs to the decoder. For those of you that don't know about binary arithmetic, you can get 15 possible combinations of on/off with 4 digits. (e.g., "0000", "0001", "0010", ..., "0111", "1111"). This is also how you count in binary, or base-2. Remember that the display driver is only interested in 10 of the 15 possible combinations, the ones that represent the numbers 0 - 9, or "0000" - "1001". Any other input combinations will result in unpredictable outputs from the decoder, so we label these as "don't cares", since we know they will never happen under normal circumstances.

The digit driver circuit consists of an MPS-A42 transistor and a 2N5401 transistor connected in a circuit that acts as a switch. Normally with no input signal applied, the switch is off, keeping the high voltage supplied by the HV Regulator away from the display. There are 6 digit signals provided by the MPU, one for each digit. The MPU will enable one signal at a time, telling the display driver which digit to operate. This signal will then turn on the "switch" for the digit, allowing the high voltage a connection to the proper pins of the glass display to energize the desired digit. These signals from the MPU are simply 6 wires and the MPU will activate one of them at a time. Like the segment signals, the six digit signals go to all of the displays in a daisy chain fashion.

OK, before I explain how the computer makes all this work, let's sum up: A display driver has four inputs from the MPU. The first is a collection of six signals used to tell the display driver which digit to energize (six digits in the display, six digit signals). Only one of these signals are on at a time. The second input is a collection of four signals that tell the display driver which number to display, in the form of segments. These four signals provide a binary pattern that is interpreted as a binary number from 0 to 9. The third input is a strobe signal, which tells the decoder to read it's inputs, and the fourth signal is a blanking signal, which tells the decoder to turn off all it's outputs. Also, but not mentioned above, are various voltages from the power supply and high-voltage regulator. Each display driver is supplied with +5VDC from the 5-volt regulator on the solenoid driver board. This is used to drive the logic circuits of the decoder. There is also +190VDC* applied to the display driver from the high-voltage regulator on the solenoid board. Finally there is a connection to ground, which brings all the voltages to the proper reference point.

• For brand new displays, this voltage should be at +190VDC in order to "burn in" the display. Once a display has become used, this voltage may be backed down to +170VDC, which will work just fine and will help prolong the life of the display.

3.10.2 How The Computer Controls The Display

OK, so now you know how the display works. The next thing to understand is how the computer in your pinball machine operates the displays. For this article, we'll refering to the AS-2518-17 Bally MPU Module, but all this also holds true for the "-35" MPU module as well. And again, I'm only refering to the Bally AS-2518-21 and AS-2518-15 Display Drivers. I've not studied the Stern style display driver, but I'd guess they behave about the same.

As mentioned above, there are four sets of signal lines that go from the MPU module to the display driver modules. The first set is the BCD data set which carry the display segment BCD data to all the displays on 4 wires. They leave the MPU module (A4) at connector J1, pins 25-28 and visit every display driver module at connector J1 and pins 16-19 (D4 - D0). The next set of signals is the digit enable signals. These 6 wires carry signals to all the display driver modules with information telling it which digit to light. The third set of signals are 5 latch strobe signals. There is one separate signal for each display driver, and it is the signal that tells the driver's decoder to read the decoder inputs, and output the proper segment signals. The final signal is a single single that goes to all the display drivers called Display Blanking. The signal tells the display driver's decoder to turn off all segment outputs, thereby blanking out the display, or turning all segments off. Below is a diagram of all the connections between the MPU module and the display driver modules that have to do what we're talking about.

Once the machine has been turned on and has booted up, the processor on the MPU module is continuously running a program that is stored in the module's ROM chip(s). This program is responsible for controlling the game by reading all the switches, lighting all the lamps, activating all the solenoids, and controlling the displays. The program keeps a lot of information in RAM and uses this information to keep track of scores, switches, etc. An interrupt is a term for a section of computer program that interrupts the "main" program in order to execute a smaller program, sometimes referred to as a "service routine". We won't get into just how this actually happens, just be aware that the main program of a computer may be interrupted at any given time. And to make things even more complicated, interrupts themselves can be interrupted by higher priority interrupt service routines. There may be several different interrupts that occur in a pinball's computer program, but the one we want to study is the one that controls the displays. Keep in mind what was mentioned above, that at any given instant, only one digit is lit on any display. This is called multiplexing.

320 times a second, or once every 3-1/4 milliseconds (thousands of a second), the CPU is interrupted to service the displays. In memory, the CPU keeps track of all the information it needs to operate all the displays. This information includes a counter used to indicate which display digit is active, the BCD data for all the displays, etc. Here's what the display service routine actually does:

Determine which digit was updated last time - The MPU looks at the digit counter and adds 1 to this value. If the new value is 7, it is changes to 1, then the new value is stored back into memory. Let's assume the new value is 4, so we're going to update the 4th digit.

Blank out all the displays - The CPU raises the signal on the Blanking Line which causes all displays to go blank (the blanking signal tells all the decoders to turn off their segment outputs).

Fetch the BCD data from memory - The BCD data for the first display, 4th digit is fetched from memory.

Send the BCD data to the display driver - This BCD data is placed on the BCD data bus and display #1 is strobed. This will cause the display's decoder to latch onto the input signals (store them for future use).

'Do it again - The previous two steps are repeated for the second, third, fourth, and fifth display.

Enable the digit - The MPU then enables the 4th digit and disables the other 5 digits by raising and lowering signals on the Digit Enable lines.

Finally, turn the digit on - The MPU lowers the signal on the Blanking Line, which causes the all of the decoders to output their proper segment signals and the 4th digit on each display is displayed.

All done! - The interrupt service routine then exits and control returns to the main program

As you can see, the display interrupt service routine only handled 1 digit for all displays. Every time it is invoked, it will process the "next" digit, resetting the counter back to 1 when necessary. The process of updating 1 digit for all displays takes about 500 microseconds, or 1/2 of a millisecond, to complete. Pretty cool, heh?

So, lets do some math. It takes 1/2 millisecond to update one digit, and since there are 6 digits, it takes 3 milliseconds to display all six digits. Since the interrupt runs 320 times a second, and it takes 6 interrupts to update the entire display, dividing 320 by 6 means that the displays are completely updated just over 54 times every second. That's fast enough to fool your eyes and brain into thinking the display is completely lit all the time. Also, since the interrupt routine takes about 1/2 millisecond to run, and it runs 320 times every second, that means about 160 milliseconds of every second of time is spent updating the displays, which is about 16 percent of the time.

--Stevekulpa 22:34, 24 April 2011 (BST)

3.11 How To Hook Up a Bally AS-2518-18 Rectifier Board

Often folks buy a new or used rectifier board and then when they get it, they realize that they have to hook it back up to the old wiring harness. If this is you, and you forgot to take notes or pictures before you removed your old board, then here you go. The photo below shows an original AS-2518-18 rectifier board connected to a factory wiring harness. As far as I know, the wire colors are the same for ALL AS-2518-18 applications.

Key:

E1 - Red 18 AWG - Transformer Lug 5 - Primary AC Hot

E2 - Yellow 18 AWG - Transformer Lug 1 - Primary Neutral

E3 - Red 20 AWG - Transformer Lug 2 - Solenoid Bus Hot

E4 - White/Red 20 AWG - Transformer Lug 6 - Solenoid Bus Neutral

E5 - Green 20 AWG - Transformer Lug 8 - Display High Voltage Hot

E6 - White/Green 20 AWG - Transformer Lug 10 - Display High Voltage Neutral

E7 - Blue 18 AWG (2 wires) - Transformer Lug 17 - GI Bus Hot

E8 - Black 18 AWG (2 wires) - Transformer Lug 18 - GI Bus Neutral

E9 - Orange 18 AWG - Transformer Lug 13 - Controlled Lamp Bus Hot

E10 - Green 18 AWG - Transformer Lug 14 - Controlled Lamp Bus Neutral

E11 - White 20 AWG - Transformer Lug 15 - 12V Input for 5-Volt Regulator Hot

E12 - White/Black 20 AWG - Transformer Lug 16 - 12V Input for 5-Volt Regulator Neutral

AWG = American Wire Gauge (18 = fat, 20 = skinny)

"E" solder pads are labeled on the top side of the circuit board

--Stevekulpa 21:08, 22 April 2011 (BST)

3.12 How To Hook Up a Stern TA-100 Rectifier Board

As Steve mentioned above when you replace or remove and reattach your rectifier board you need to know how to hook it back up. I have done this with a lot of Stern pins and made myself a chart for quick and easy reference when re-attaching the rectifier to the transformer. I figured it may be useful to others as well.

3.13 Bally Auxiliary Lamp Driver Boards

Bally AS-2518-52 Aux. Lamp Driver Board

Bally AS-2518-43 Aux. Lamp Driver Board (Midway A084-91614-A000 pictured - same as AS-2518-43)

3.14 Bally Sound Boards

Bally AS-2518-32 Sound Board

Bally AS-2518-50 Sound Board

Bally AS-2518-51 Sound Board

Bally Cheap Squeak Sound Board A080-91603-XXXX Midway P/N M-051-00114-XXXX

Cheap Squeak is used in the following games:
Black Pyramid - Cybernaut - Fireball Classic
King Of Steel - Spy Hunter - X's & O's
----------------------------------------------
EPROM Configuration	Jumpers Connected
U3&U4 using 2532s	J6, J9, J12
U3&U4 using 2732s	J7, J10, J11
U3 ONLY using 2764 (may not work in all games)	J2, J4, J7, J11

Bally AS-2518-61 Squawk & Talk Sound Board

Bally AS-2518-61a Squawk & Talk Sound Board

File:AS-2518-81-2.jpg

Bally AS-2518-81 Say It Again Sound Board

3.14.1 Bally Sound Board Pinouts

Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J1-1	Sol. Address A	Sol. Address A	Sol. Address A	Sol. Address A	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 0	Sound Select 0
J1-2	Sol. Address B	Sol. Address B	Sol. Address B	Sol. Address B	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 1	Sound Select 1
J1-3	Sol. Address C	Sol. Address C	Sol. Address C	Sol. Address C	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 2	Sound Select 2
J1-4	Sol. Address D	Sol. Address D	Sol. Address D	Sol. Address D	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 3	Sound Select 3
J1-5	+5VDC	+5VDC	+5VDC	+5VDC	N/U	N/U	N/U	N/U	N/U	N/U
J1-6	Ground	Ground	Ground	Ground	Ground	Ground	Ground	Logic Ground	Logic Ground	Logic Ground
J1-7	N/U	N/U	N/U	N/U	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	N/U	N/U	N/U
J1-8	Sol. Bank Select	Sol. Bank Select	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt
J1-9	+43V	+43V	N/U	N/U	N/U	N/U	N/U	N/U	N/U	N/U
J1-10	N/U	N/U	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+14V Unregulated	+14V Unregulated
J1-11	Key	Key	Key	Key	Key	Key	Key	Key	Key	Key
J1-12	Sol. Address E	Sol. Address E	Sol. Address E	Sol. Address E	Sound Select	Sound Select	Sound Select	N/U	N/U	N/U
J1-13	N/U	N/U	N/U (Spare Address Line)	N/U (Spare Address Line)	N/U	N/U	N/U	Earth Ground	Earth Ground	Earth Ground
J1-14	Ground	Ground	Ground	N/U (Ground)	Ground	Ground	Ground	Logic Ground	Logic Ground	Logic Ground
J1-15	+43V Return (Sol. Ground)	+43V Return (Sol. Ground)	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+14V Unregulated Return	+14V Unregulated Return
J1-16	n/a	n/a	n/a	n/a	n/a	+12V Unregulated Return	+12V Unregulated Return	n/a	n/a	n/a
J1-17	n/a	n/a	n/a	n/a	n/a	+12V Unregulated	+12V Unregulated	n/a	n/a	n/a
J1-18	n/a	n/a	n/a	n/a	n/a	N/U	N/U	n/a	n/a	n/a
Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J2-1	Speaker +	Speaker +	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -	Speaker Return	Speaker Return
J2-2	Speaker -	Speaker -	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +
J2-3	n/a	n/a	n/a	n/a	Key	Key	Key	n/a	Key	n/a
J2-4	n/a	n/a	n/a	n/a	Remote Volume Return	Remote Volume Return	Remote Volume Return	n/a	N/U	n/a
J2-5	n/a	n/a	n/a	n/a	Speech Volume	Speech Volume	Speech Volume	n/a	N/U	n/a
J2-6	n/a	n/a	n/a	n/a	Sound Volume	Sound Volume	Sound Volume	n/a	N/U	n/a
J2-7	n/a	n/a	n/a	n/a	n/a	n/a	Reverb Audio In	n/a	n/a	n/a
J2-8	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	n/a	n/a	n/a
J2-9	n/a	n/a	n/a	n/a	n/a	n/a	Audio Out	n/a	n/a	n/a
J2-10	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	n/a	n/a	n/a
Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J3-1	n/a	n/a	n/a	n/a	n/a	n/a	Ground	n/a	n/a	n/a
J3-2	n/a	n/a	n/a	n/a	n/a	n/a	Data	n/a	n/a	n/a
J3-3	n/a	n/a	n/a	n/a	n/a	n/a	Clock	n/a	n/a	n/a
J3-4	n/a	n/a	n/a	n/a	n/a	n/a	+5VDC	n/a	n/a	n/a
J3-5	n/a	n/a	n/a	n/a	n/a	n/a	Key	n/a	n/a	n/a
J3-6	n/a	n/a	n/a	n/a	n/a	n/a	PB3	n/a	n/a	n/a
J3-7	n/a	n/a	n/a	n/a	n/a	n/a	PB2	n/a	n/a	n/a

3.15 Stern Sound Boards

Stern SB-100 Sound Board - 1st Version

Stern SB-100 Sound Board - 2nd version (less populated)

Stern SB-300 Sound Board

4 Problems and Solutions

4.3 Solenoid problems

Before proceeding to diagnose solenoid or problems, see this section: How coils are turned on

4.4 Lamp problems

Most lamp problems stem from the sockets themselves. The recommended best practice for problem sockets is to replace them. If you want to try and get them working reliably, here are some things you can try:

First off, clean the inside of the socket. There are nice dremel tool tips to help, but even a screw driver can scratch off some crud from inside a socket. Some time a light squeeze on the socket with pliers can make the bulb stay in nice and snug and be less likely to move and stop lighting.

The bare wire running under the playfield for controlled lamp power carries 5-6 vdc and is usually soldered onto the sockets mounting bracket. The mounting bracket then connects to the outside of the socket. After 30 years or so the connection from the mounting bracket to the lamp socket's outside can break. To remedy this there are two things you can try. You can solder the barrel of the lamp socket directly to the base of the socket (so it can no longer swivel). This can be kind of tricky without a higher power soldering iron - if you use paste flux it is easier. Radio Shack also sells a solder called "Crystal Clear" flux which works well. To do this well you need to either sand or file (the file works best and saves your fingers) the area to be soldered on the base and the barrel. The other option is to run a small jumper wire that connects the bare wire directly to the outside of the socket, thus eliminating the poorer connection between the mounting bracket and barrel.

Another less common issue is the connection between the lamp socket's solder lug (insulated wire to the driver board connects here), and the back tip of the socket (what moves out/in and is spring loaded to hold bulb in place). What you can do here is to move the insulated wire off of the lamp socket's solder lug and solder it directly to the back of the socket tip. This eliminates any potential connection issues with the solder lug/tab and the back pin.

Before soldering onto a socket, either the barrel or the spring terminal, it must be sanded or filed clean or the solder will not stick. Paste flux or the crystal clear flux solder recommended above will help. If you have a temperature controlled soldering station crank it up above what you would normally use for boardwork to about 800 degrees.

Another issue is the multiple lamp mounting boards/brackets like those used in Stern Big Game, Meteor, and others. The lamp sockets are riveted to these mounting boards and are not replaceable. These mounting boards suffer from a bad connection to the bare controlled lamp wire running under the playfield. You can either solder each lamp barrel to the base plate or run a daisy chain wire from barrel to barrel to help fix issues with the sockets.

Again, lamp sockets need to be sanded (200 grit works good) or filed before solder will stick. (see picture, below)

If your lamp is always stuck on then the SCR driving it is bad. Bally/Stern use two different SCR to control lamps. MCR106 is able to drive up to two lamps at the same time. The smaller 2n5060 will only drive one lamp. These SCRs do fail from over sinking of current, from old blackened bulbs (which draw more current) or from being shorted to something under the playfield carrying a high voltage (solenoids). If you accidentally short several lamps together, this would cause the SCR to fail also.

If you are in a bind it is possible to use the more robust MCR106 in place of a 2n5060 with one caveat. Two legs of the MCR106 SCR need to be reversed to be used as a replacement for a 2n5060. As you are looking at the board the top and middle leg of the MCR106 need to be reversed. (see picture, below)

• • note ** a 2n5060 CAN NOT be used instead of a MCR106

Still can't get your controlled lamp to light up and you're sure it's wired up right and getting power? A lamp that never lights might be a bad SCR that needs to be replaced or the connection that runs from the lamp board to the lamp. Use your DMM on continuity test to follow the path from the SCR to the lamp itself to find out if it is a connector issue.

On some lamp boards there are buffer and decoder chips. A bad buffer or decoder chip can prevent a lamp from lighting. If you have multiple lamps out and you have tested the wiring for each, look back to the chips to see if the lamps out have a chip in common. (Refer to the games' schematics) If so, and you have tested the SCR's as good, the chip is probably bad. The .100 headers on the lamp driver boards are subject to a lot of stress and should be resoldered to ensure there are no hairline cracks in the connectors.

All Controlled lamps not working:

Could be rectifier board connectors, bad lamp bridge rectifier, or fuse blown.

Dim controlled lamps:

The biggest cause of dim controlled lamps is a weak connection via the power chain's connectors. The original lamp driver bridge rectifier is slightly undersized on the rectifier board at 8 amps; either changing to #47 bulbs can alleviate some of the load placed on this bridge, or it can be upgraded to a larger capacity (25 amp-up). Changing the header pins on the rectifier board to a 10 amp capable pin plus changing the connector pins will help the power chain. Application of a dielectric to prevent oxidation can help prevent new pins from prematurely wearing out, but do not apply any chemical to old, tarnished pins.

The fuse clips on the rectifier board can get tarnished, too. Replacement with high current phosphor-bronze clips will help dimming issues. The less resistance in the power chain the better and brighter your lamps will be.

--barakandl 19:00, 12 May 2011 (EST)

4.6 Display problems

4.6.1 Display High Voltage Section

Bally High Voltage Section Repair

WARNING: This circuit uses high voltages. Don't continue, unless you are confident in your diagnostic abilities.

If all displays are blank, your high voltage (HV) section may not be working. On the Solenoid Driver Board (SDB), use a DMM to measure volts DC on test points TP2 and TP4, to determine if this section needs repair:

TP2 = 150 to 190VDC
TP4 = 230VDC +/- 25VDC

If TP2 is less than about 150VDC or over 200VDC, the HV section is malfunctioning. If TP4 is 0VDC, then power is not getting from the Power Supply board, and the problem is located either on the Power Supply, or in the wiring/connectors carrying power to the SDB, so you must correct this before working on the HV section.

Replacing the components in the HV Section
(TP2=0VDC or 230VDC AND TP4=230VDC)
If you prefer to replace only the failed components, follow page 50 of the Bally repair manual, F.O. 560, dtd 20 June 1977. http://gamearchive.askey.org/Pinball/Manufacturers/Bally/pdfs/ballyfo560.pdf

Since there are not that many components, it is may be less time consuming to replace all the components in the HV section. Most of these components are located between the two large heat sinks.

Check the parts section of the wiki to find suppliers, and get the following replacement parts (1/2 watt resistors can be substituted for 1/4 watt).

Part	Part No.	Location
Transistor	2N3584,250V,2A,NPN	Q21
Transistor	2N3440,250V,1A,NPN	Q22,Q23(heatsink)
Zener diode	1N5275A,140V,1W,5%	VR1
Diode	1N4004,400PIV,1A	CR21
Fuse	3/16A,8AG	F1(-22 only)
Resistor	22k Ohm,1/2W,5%	R51
Resistor	1.2k Ohm,1/4W,5%	R55
Resistor	82k Ohm,1/2W,5%	R56
Resistor	8.2k Ohm,1/4W,5%	R54
Resistor	390 Ohm,1/4W,5%	R52
Resistor	100k Ohm,1W,5%,metal film	R35
Capacitor	0.01 uF, 400V metal polyester	C27,C28
Capacitor	150 uF, 350V (if original, replace)	C26
Potentiometer	25k Ohm, PC-mount	RT1

Remove and replace components

• Clip the old components from the board (make sure you have new ones first).
• Use one of the desoldering methods to remove solder from the holes.
• Stuff board with new components.
• Check for correct orientation on transistors, diodes and the large capacitor if you replace it.
• Leave a little space under components for air flow.
• Bend leads on components so they won't fall out when board is inverted for soldering.
• Double check that all the correct parts are in the correct places and properly oriented.
• Solder the parts to the board
• Clip excess off leads

Ready to test

Prior to powering up and testing, remove all display connectors, or test with F1 removed from the SDB. I recommend connecting your DMM with a clip lead to TP2 prior to powering the game, so you don't have to probe the HV section. Power up the machine and verify TP2 voltage is 150VDC to 190VDC. If the correct voltage is read, power down the machine and reconnect all the displays and put F1 back in. Leave your DMM connected to TP2.

Power up the machine and adjust RT1 so TP2 reads about 150VDC to 160VDC. If some of the displays no longer light, then adjust the voltage up until they are all lit.

New displays may require to be burned in at 190VDC for an hour or two, but then the voltage can be reduced. The lower voltage will prolong the life of the gas plasma displays.

If TP2 is not correct after your repair, you will need to recheck your work. If you cannot find a problem with your repair, then I recommend you follow the troubleshooting steps on page 50 of the Bally repair manual, F.O. 560, dtd 20 June 1977. http://gamearchive.askey.org/Pinball/Manufacturers/Bally/pdfs/ballyfo560.pdf

After you have repaired your HV section and verified that it is providing the correct voltage, the next section will help you fix problems with the displays.

4.6.2 Repairing Bally/Stern Displays

This page will help you repair your Bally 6- and 7-digit displays. The information is focused on the AS-2518-21 display. Since the AS-2518-15 display is interchangeable with the "-21" display, everything mentioned here will apply to both displays. Bally 7-digit displays (AS-2518-58) work the same way, they just contain additional components to support the additional digit, and lighting of commas. Some Stern DA-100 6-digit displays are very similar to the Bally versions, and the information here will also work for them. The Stern 7-digit display is slightly different, as its circuit board is physically deeper than any of the other displays and is not directly interchangeable with a Bally 7 digit display. Additionally, there are some input pin differences; however, if you have the schematic you can use the information here on the display, some transistors might be labeled differently.

First off, let's make sure your malfunctioning display is even repairable. If the glass display itself is shot, there's not much that can be done except to replace it. Here's a couple of photos of things that can go wrong with the glass display.

Burn spots on the digit segments - You can't fix these but you can live with them

Broken glass nipple - This display glass is ruined

Then there's the circuit board. Most if not all of the components can be replaced without much effort, but if there is damage to the circuit board itself, it may be impossible, or unreliable to repair.

Burn marks on the driver board

Underneath - The traces are a mess

So we're assuming you have displays that do not fall into the categories above. If your problem is with the digits not being displayed properly, and it's NOT the MPU's fault, then it can be fixed, and fairly easily too!

FIRST THING - Before you go any further, there are two things you should do to ALL your displays, even if they seem to be working fine. First, reflow the solder on the joints for the header pins. On the bottom side of the circuit board, just heat each header pin solder joint with your soldering iron, then add a little fresh solder. Be careful not to create any solder bridges between adjoining pins, unless there is already one there. Next, replace the six 100K ohm 1/4 watt resistors with 1/2 watters. They are the ones with the color code brown-black-yellow, and are labeled R1, R3, R5, R7, R9 and R11. You'll find seven of them, but only the ones I just listed need to be replaced. For 7-digit displays there will be eight of them, so replace R56 too, along with the six I just mentioned. 1/4 watt is just too small for their circuits and often they are overheated which causes them to change their resistance. On the photo of the burnt circuit board up above, the area that was burnt was under 3 of these resistors.

SECOND THING - Connectors, connectors, connectors! There are lots of signals going from the MPU to each display driver, and if these signals are not making it due to bad wiring or connectors, then your displays will misbehave. Check all the display driver connectors for loose or broken wires, burnt pins, busted connectors, and replace or repair anything that looks bad. Remember that some of the signals are daisy-chained from display to display, and a bad connection at one display can effect the others "downstream". Then check the J2 connector on the MPU, since this is where all the signals come from. Next check the J3 connector on the solenoid driver board. There's a high voltage regulator used by the displays on this board, and J3 is where it gets the 230 VDC from the power supply (pins 6 & 3) and feeds the regulated 190 VDC to the displays (pin 8). Finally, check the J3 connector on the rectifier board, since this is where the high voltage comes from. Connectors are always a big pain!

Header pin solder joints - Notice the cracks around the last two pins on the right

Header pin solder joints after being re-soldered - No cracks

Can you find the six 100K ohm resistors (brown-black-yellow)

Here they've been replaced them with 1/2 watt resistors of the same value (100K ohms)

Now we'll look at come common problems and briefly describe the cause, but I assume you've already replaced or checked the 100K Ohm resistors and re-soldered the header pins:

All displays are blank

Most likely cause of all blank displays is a lack of high voltage. First off, check F2 on the rectifier board. It's a 3/4 Amp slow blow fuse and it's test point on the rectifier board is TP2. You should read 230 VDC at this test point. If it's OK, then check the fuse on the solenoid driver board. The high voltage regulator's output is fused and if this fuse is blown then there's probably a short somewhere on one of your displays or the wiring harness. The high voltage regulator fuse is a 3/16 Amp, but it's a bit smaller (8AG) than a standard fuse, and a hard one to find. If the fuse is not blown, then the next thing to do is verify that at least 170 VDC is making it from the regulator to the displays. Check TP2 on the solenoid driver board. It should read between 170 and 190 VDC. If it does, then the regulator is working. While you're there, if your display glasses are not new, use the small trimmer pot on near the fuse and adjust the high voltage to be 170 VDC. Older displays work just fine on 170 VDC and it's less stressful.

Next thing to check is to be sure that the 170 volts is making it to the displays. Check connector pin J3-8 on the solenoid driver board, that's where the 170 VDC leaves. Check for a good connector, and check the solder joint on the header pin. The high voltage hits all of the displays at connector J1-1 and is daisy-chained from display to display. Check these connectors and the header pins too.

Note - If there is any light at all on the display, then it is probably repairable. Some type of Bally display glasses will have some light on them, besides the digits. If there is light anywhere on the display, then the glass is most likely OK and your problems are elsewhere.

See how this display is glowing when it's first turned on? This indicates that the glass is good.

.

REMEMBER - 170 VDC WILL HURT!
TURN YOUR MACHINE OFF IF YOU'RE GOING TO MESS WITH IT BEYOND MEASURING VOLTAGES

If you have 170 VDC at all of the displays, and the decoder is still working, but the displays are still blank, then there is probably a problem on the MPU or the MPU connectors, such as a "stuck-on" blanking signal, etc.

A single display is blank

If you have one display that is blank, it could be the same problems as mentioned above (lack of 170VDC), something wrong on the circuit board, or something with the glass display itself. If you see any light glowing at all on the display, then the glass is most likely good and your problem is elsewhere.

The main cause of a single display being blank is a bad glass. If the glass is good, then your problem is most likely a bad 4543 decoder IC. The decoder on the display driver board is used to decode the digit data from the MPU into signals that light the proper displays. If the decoder is blown, then this could cause the display to be blank. A quick check with a logic probe will help you decide if the decoder is function properly.

Sometimes the solder joints on the display glass needs are cracked and need to be reflowed. Depending on which solder joints are bad, this could cause the display to be blank.

If you can verify there is 170VDc, and the decoder is working, then it may be just a bad display. If there is some light anywhere, then it's probably good. If not, it may or may not be good. A totally blank display is the hardest thing to fix. If everything looks good, but the display is completely blank, then you may just have to chalk it up as a bad display glass. Unfortunately they can not be repaired.

All displays are missing the same digit

If all the displays have the same digit out, then the problem is most likely caused by a bad connector at the MPU. The MPU daisy-chains the digit enable signal to all the displays, and if the same digit is out on all, then it's either an amazing thing that they all have a problem w/ the same digit, or the digit enable signal is not present. Check the connectors on the MPU and all of the displays. If all seem well, then one-by-one, disconnect each display and see if the problem goes away. If it does, then there's a short or a bad connector problem on the board you just removed. Be sure to turn the power off between swap-outs, and wait 10 seconds for the high voltage filter capacitor to discharge before you remove any connectors.

One display is missing the same segments on all the digits

Each display has it's own decoder chip, which takes four inputs from the MPU and outputs seven signals to light the seven segments of a digit. If you're having problems with one or more segments on all the digits, then it's either the segment driver transistor or the decoder itself. I'm sure there's a way to test the transistor but I just go ahead and install a new one. If that doesn't fix it, then replacing the decoder will. I've not had a segment problem that was not fixed by replacing both segment drivers and decoders (other than MPU problems). Be sure to orient the transistor and/or IC in the proper position. You'll notice a flat side on the transistor and a small notch on one end of the decoder IC. Be sure they line up just like the one you removed, and that the wires of the transistor go into the same holes that the old one came out of. Also, if you're replacing the IC, use a socket, so it'll be easier to replace it next time. Here's a handy chart that shows which segment driver transistor drives which segment, and another diagram of how the segments are labeled. Just find the segment that's giving you trouble on the chart, then look up it's corresponding driver transistor. Then find this transistor on the circuit board and replace it.

One digit is out on one of the displays

If you have a single digit out, then it's probably the the level shifter and digit driver transistors for that digit. Just to be sure, check the connector on the display at pins J1-4 through J1-9. These are the connectors that supply the digit-enable signals from the MPU. Your problem may be that the display driver is not getting the enable signal from the MPU. If it is, then just replace the two transistors and you should be back in business. Here's a handy chart that shows you which level shifter and digit driver are associated with each digit. You'll find the transistor labels printed on the circuit board, or look at the diagram below. Just look at this chart, find the digit that's blank, and then locate the two transistors listed for that digit. Find them on the circuit board and replace them.

One digit is very bright, and the rest are out

If you have one digit that's very bright and all the rest are out, simply replace the digit driver and level shifter transistors for that digit. Turns out sometimes a short transistor will draw so much current that there's not enough left to drive the remaining digits, and so they all go blank. Just use the chart above to determine which transistors to replace.

Display(s) flicker

This is almost always caused by broken solder joints on the header pins. If you already re-flowed the solder, double check them, then look for other broken solder joints and check all connectors for tight fits. Something is loose that's making them flicker.

Another cause of flickering or strobing digits is a faulty decoder IC. If your digits are flickering or "wavy", try replacing the decoder IC.

Conclusion

That covers the most popular problems. I hope it covers yours. If you don't have the manual for your pinball machine, click on any of the thumbnails below for a large picture of the component layout of the all three boards. The 100K Ohm resistors are the ones colored brown-black-yellow.

4.6.2.1 Display Examples

Here are the 3 types of Bally displays:

AS-2518-21 6-Digit Display

AS-2518-15 6-Digit Display

AS-2518-58 7-Digit Display

--Stevekulpa 00:13, 25 April 2011 (BST)

Here is the Stern DA-300 display. Note that the circuit board is deeper than any of the other display types.

4.9 Setting Free Play

If you read the manual that came with your game, you'll notice there are no factory provisions for setting the games on non-coin play. There are several options for homeowners to set their machines up so quarters or opening the coin door aren't required.

Free play via low replay scores

The easiest way to keep a quantity of credits on the machine is to set the first replay score to a very low value (10,000 on most machines). This way you can put several credits on the machine initially, and then each game played will probably win a credit. Press the self-test button inside the coin door until you see "01" in the ball-in-play display. Press the button on the mpu board itself (S33) to clear this value to zero, then use the credit button (on the coin door) to step the setting one click forward to 10,000. (Some games let you 'flick' a coin door switch to zero the value, S33 works for all games)

In most cases you will score 10,000 very quickly enabling the machine to self-replenish their credits.

Free play via adding a switch

If you like having the 'coin-up' sound most machines make, adding a free play switch to a game is relatively simple. Any type of normally open switch can be soldered to one of the coin switches and mounted in an unobtrusive way (through the coin door return is a popular example, or mounted to the coin return instead). While it is also possible to drill a hole in the cabinet or coin door to mount this type of switch, it is discouraged to do this as it is difficult or impossible to reverse cleanly.

This type of switch can be piggybacked onto the credit button switch itself, the initial full press will add a credit, and the pullback stroke will start a game.

Free play via ROM replacement

As of this writing, free play replacement ROMS are available for all Bally/Stern games. For many years only Bally freeplay roms of various flavors were available, and these romsets are incorporated into some of the aftermarket replacement MPU boards. In 2009 freeplay roms became available for all the stern mpu-100 and mpu-200 games as well, but as of yet (5/2011) are not incorporated into any aftermarket boards.

Some varieties of free play roms never let the credits go below one, some require a DIP switch setting, and some are free play only. Regardless of the type of free play rom used, they all work similarly. When the credits fall below a certain amount, the software code either increments a credit automatically, simply allows a game start with credits showing 00, or never let the credits decrement below 01.

For many people free play roms are the preferred method of handling free play as no hardware modifications are needed to incorporate free play, and you can still have replay levels set to challenging levels. It also allows the machines to be placed in clubs, businesses, shows, etc. without the owner having to worry about people not knowing how to add credits via some other method. Press the credit button and go.

5 Game Specific Problems and Fixes

5.1 Bally/Stern LED stays on after boot

7th flash produced but no led dimming afterward: The problem was one of the capacitors around the u12 (clock signal) was bad. I replaced c12,c16?, and c17. After that I got the 7th flash and the dimmed led afterward

---

5.2 Solenoid expander board

There is a 555 bulb near (or sometimes not so near) that lights when the solenoid expander is activated. This bulb is essential for proper operation of the expander as the main opto isolator chip on the expander board needs a load to work; if you're having entire sets of solenoids not working, check this bulb.

The header pins on this board like to crack, also, so standard operating procedure should be to replace or at minimum resolder the headers, and re-pin the connector with Trifucon connectors.

Also, it's very important that all solenoids on the expanded circuits have *TWO* diodes on them! If you or someone in the past replaced the coils with one that one had one, multiple solenoids will activate on any solenoid expanded solenoid, causing a memory drop to activate when it shouldn't, or a target bank reset when a saucer ejects.

---

5.3 Stern SB-300 sound board modification for VSU-100 usage

Games with a VSU-100 speech card require a modified SB-300 to utilize the speech. First, see if your SB-300 already has a trace for this connection by checking continuity between pin 5 of the rightmost connector at the bottom and the top of capacitor C14. If you read continuity, you do not need to do this mod. Add a jumper wire on the back of the SB-300 between pin 5 of the rightmost connector Media:sb300sig3.jpg and the top of capacitor C14 Media:sb300sig2.jpg. Here is an overall picture of the entire jumper for reference: Media:sb300sign1.jpg

---