Baby Pac-Man
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1 Introduction
Baby Pacman (Also: Baby Pacman) was produced in 1982 by Bally. Baby Pacman is one of the few hybrid video/pinball games that were ever produced, and only one of two hybrid games produced by Bally.
2 Technical Info
2.1 System Overview
2.1.1 Prototype
There were 4 or 5 half-height prototype games made. One of them is in Todd Tuckey's personal collection (owner of TNT Amusements). Baby Pacman gets its name from these prototypes since they were originally intented to be a "baby-sized" arcade game, when compared to full-sized arcade games.
2.1.2 Production Game
(TODO: photos of the game)
2.2 Boards
2.2.1 MPU
This game uses a Bally AS-2518-133 MPU. This is nearly identical to the AS-2518-35 board, with a few minor differences. A -35 board can be converted to a -133 board and vice-versa by swapping a few through-hole components. See the notes on this conversion process on the main Bally/Stern page.
This game uses two ROMs. A 2732 eprom at U6 and a 2532 eprom at U2. The MPU board can be re-jumpered to accept two 2732 eproms.
The diagnostic LED flash sequence is slightly different on the -133 board than the -35 board. The -133 board's diagnostic LED displays 6 flashes, while the -35 board displays 7 flashes. (TODO: Include reason for this difference) Otherwise, troubleshooting procedures are identical to that of the -35 board.
2.2.2 Driver/Lamp
This game uses a Bally AS-2518-107 combo board to drive both the feature lamps and the solenoids. This board is also found in Bally's second hybrid game, Granny and the Gators.
Each SCR in the lower left area of the board (marked as Q1 through Q28) is responsible for driving two lamps. If one of the SCR's fails, usually a pair of lamps won't respond and will either be stuck either on or off.
If the MPU is not working or not communicating with the vidiot board, the driver board will still turn blink the feature lamps on and off haphazardly, but they will not be sequenced. When the MPU is working properly, the lamps will turn on and off according to a specific sequence.
2.2.3 Vidiot
This game uses a Bally AS-2518-121 Video board to display output on the monitor, output sound, and receive input from the control board's joystick and buttons. Because this board is reasonably complex and unique, it can be a central point of failure in this game. A modified version of this board named the "Vidiot Deluxe" board was used in Bally's second hybrid game, Granny and the Gators. The two boards are different enough to not be cross-compatible.
Four 2764 eproms are used for the video section of the vidiot board at U9-U12. The sound section of the board uses one 2764 eprom at U29.
The vidiot board can be tested for sound and video without needing the MPU.
2.2.4 Rectifier
This game uses a standard Bally AS-2518-132 rectifier board.
Since this game does not use any score displays (like normally found on a pinball machine), the +230VDC (190VDC unregulated) found at TP2 is not used. This means that it is not necessary to install a fuse at F2.
The -132 board is very similar to an AS-2518-54 rectifier board, but with a few modifications/improvements. The -132 board uses 6 amp diodes at CR5 through CR8, while the -54 board uses 3 amp diodes. The 6 amp diodes provide better heat dissipation. The -132 board uses two circuits for the general illumination, and thus also uses two separate fuses (found at F5 and F6). This allows for more lamps by spreading the load between two circuits. The early revision of -54 board only uses one circuit and one fuse, however, AS-2518-54 revision B includes two circuits and two fuses for the general illumination.
The Fuse values differ between the -132 and -54 boards.
2.3 Monitor
This game uses a 13" video game monitor mounted vertically.
(TODO: include more details about the monitor and possible replacement options)
2.4 Speakers
This game uses two oval 3"x6" (TODO: Verify measurements) 4 Watt 4 ohm speakers in mono, which are mounted above the coin door on the inside of the cabinet. If necessary, a single 4 Watt 8 ohm speaker can be used (Note: Do *not* use two 8 ohm speakers!)
2.5 Playfield
Baby Pacman has two distinct types of playfields. An earlier version of the playfield uses a matrix of lamp sockets for the feature lamps. A later version of the playfield uses a circuit board with twist-on sockets. The version with the lamp sockets was considered to be difficult to work on and prone to shorting out bulbs in the sockets or SCRs on the driver board.
The two different playfields appear to use different connectors, so it may not match up with the connector found in the cabinet. A pigtail adapter might be needed to adapt the playflield connector to the cabinet connector if one type of playfield is being swapped in for another.
2.6 Fluorescent Lamp
This game uses a fluorescent lamp behind the marquee, which is connected directly to the transformer.
(TODO: Include what type and size of lamp)
2.7 Bezel
There are two versions of the Baby Pacman bezel.
One version has no instructions or scoring information on the bezel. As an after-thought, Bally produced stickers which could be added to the bezel that included "escape to pin" instructions along the bottom edge of the bezel and scoring information in the lower right. These stickers had rounded corners and white backgrounds.
The second version of the bezel has instructions and scoring information included within the artwork. This is the more common version by far.
3 Problems and Fixes
3.1 Connectors
The IDC connectors in this machine are a weak link. They were a cost-cutting measure when these machines were originally built, and as a result, often fail and need to be re-pinned because either the wire pops out of the pin in the connector, or the connector pin gets too loose and can't make contact with the header pins. This can be a source of many problems. It can sometimes appear as a consistent discontinuity issue, an intermittent issue as the machine moves/vibrates, or as heat causes things to expand and possibly loose contact. It is a good idea to replace any problematic IDC connectors with molex KK-series connectors. Some individuals recommend only replacing the connectors with problems to save some time, while others recommend just replacing them all at once in order to avoid potential future issues with the IDC connectors.
The connectors can be purchased from Great Plains Electronics and Big Daddy Enterprises. The 0.100" 25-pin and 28-pin connectors have been discontinued, so they may be difficult to obtain. If necessary, two smaller connectors can be used side-by-side in place of the larger 25 or 28-pin connectors.
When re-pinning the connectors, note that there are a few pins that have two wires connected to a single pin on the MPU board's J2 connector and the Vidiot board's J8 connector. The wiring for all the connector pins can be found on page 38 in the manual on the diagram labeled "Wiring Diagram Video-Pin Cabinet".
Baby Pacman uses both 0.100" header pins and 0.156" header pins. Here is a list of all the connectors found on the circuit boards:
| Board | Connector | Pins | Pin Size |
|---|---|---|---|
| MPU | J1 | 28 | 0.100" |
| MPU | J2 | 15 | 0.100" |
| MPU | J3 | 16 | 0.100" |
| MPU | J4 | 19 | 0.100" |
| Driver | J1 | 15 | 0.100" |
| Driver | J2 | 12 | 0.100" |
| Driver | J3 | 15 | 0.100" |
| Driver | J4 | 10 | 0.156" |
| Driver | J5 | 6 | 0.156" |
| Driver | J6 | 12 | 0.156" |
| Driver | J7 | 6 | 0.156" |
| Driver | J8 | 25 | 0.100" |
| Driver | J9 | 10 | 0.100" |
| Driver | J10 | 6 | 0.156" |
| Driver | J11 | 6 | 0.156" |
| Vidiot | J1 | 28 | 0.100" |
| Vidiot | J2 | 20 | 0.100" |
| Vidiot | J3 | 12 | 0.156" |
| Vidiot | J4 | 12 | 0.156" |
| Vidiot | J5 | 2 | 0.156" |
| CRT Board | ? | 6 | 0.156" |
| CRT Board | ? | 2 | 0.156" |
3.2 Vidiot Board
3.2.1 Video
3.2.1.1 Color Bars
If the monitor displays color bars, that usually means (most of) the vidiot board is operational.
3.2.1.2 Communications Test Problems
If everything is working correctly, the communications test found in the diagnostics menu will display two columns of identical numbers.
3.2.1.2.1 Missing Number Columns
If one or both columns are missing, one or more of your connectors is not plugged in, or the connectors/pins might be dirty. Check J1 on the vidiot board. Check J1 and J2 on the MPU.
3.2.1.2.2 Missmatching Number Columns
If numbers between the receive (RCV) and transmit (XMIT RCV) columns are mismatching, that usually indicates a connectivity issues with wires, pins, or connectors.
To perform connectivity tests, the following chart may be helpful. Each column in the communications test should match the numbers under the "signal" column in the chart. If not, find the corresponding row and column on the chart, and perform continuity tests between the resistor of one side and the resistor of the other. Testing on the resistor leads ensures that pin connectivity is tested.
If connector and header pin issues are ruled out, there may be broken traces along the line as indicated by the incorrect column numbers. It may be helpful to hold the circuit board up to a light. Additionally, chip sockets may need to be removed in order to see if there was any damage done to the board before the socket was installed.
If broken traces are ruled out, the legs of a socketed chip might be tarnished. Use a pink rubber eraser to gently clean them off.
Next, replace any suspected sockets.
After that, replace any suspected chips.
3.2.1.2.3 0F Displayed in Columns
If "0F" is displayed down a receive or transmit column, that may indicate a short on one of the boards. Do connectivity tests between neighboring pins on each board to see if any of them are making contact. Keep in mind that there are a few pins that have multiple wires connected to them.
3.2.2 Sound
(TODO: Add common sound issues)
3.3 Driver Board
3.3.1 Solenoids
If the solenoids never fire, check the fuses found on the underside of the playfield.
(TODO: symptoms of a bad capacitor)
3.3.2 Lamps
On the driver board, a bank of SCR's labeled with Q## are responsible for driving the feature lamps on the playfield. Each SCR drives two lamps. The driver board schematic shows which feature lamps correspond to each SCR, however, referring this diagram should save some time.
3.3.2.1 Individual Feature Lamp Dim, Flickering, or Stuck On
There are a few symptoms which indicate a failed/disconnected/missing diode on a feature lamp. One common symptom is being "stuck" on, but at about half the brightness of other lamps. Another symptom is dim flickering, even while the lamp is off. Lastly, when the lamp is active, the lamp may be at about half the brightness of the other lamps.
The lamp socket diode can be replaced with an IN4004.
De-soldering is straight-forward, however, it might be a good idea to stuck a piece of paper or cardboard below the lamp receiving repairs so that solder doesn't drip down onto other components.
The banded side of the diode must connect to the small lug, while the un-banded side must connect to the large lug with the hole in it. Be mindful of which lug is which, as each lamp socket might be oriented in different directions from their neighboring lamp sockets.
The best way to attach a new diode is to ensure a mechanical connection first by wrapping each end of the diode around each corresponding lamp lug. A fine pair of needle-nose pliers may be needed to help accomplish this. Then, solder and trim the excess leads as appropriate.
3.3.2.2 Feature Lamps Stuck On (In Pairs)
Feature lamps that are stuck in the "always on" state typically are "stuck" on in pairs, since each SCR on the driver board drives two lamps. So, when an SCR fails, it typically affects two lamps. If a pair of lamps are stuck on, use the diagram above to find out which SCR on the board the lamps correspond to, and replace that SCR. The SCRs were originally 2N5060, but can be replaced with 2N5064, which are rated for a higher voltage.
(TODO: How to test SCRs with a multimeter)
3.4 Monitor
(TODO: How to adjust montor) (TODO: When to re-cap--symptoms)
3.5 Gameplay Issues
3.5.1 Game Displays "SLAM" on Monitor
On the coin door, a slam switch is mounted onto the lock. The slam switch on the coin door is normally open. If the slam switch is closed, the monitor displays the word "SLAM" in the center of the screen and the feature lamps on the playfield all go out. The general illumination will remain on.
3.5.2 Game Does Not Eject Ball on Button Press in Pinball Mode
The right flipper button is responsible for ejecting the ball during pinball mode. If the leaf switch is not working correctly or if the player does not press the button, the ball ejects automatically after a few seconds. If the player presses the right flipper button and nothing happens, that may indicate that there is something wired incorrectly or that the diode is missing on the right flipper switch. The right flipper is different from the left flipper since it is responsible for responding to the player to eject the ball in pinball mode.
3.5.3 Game Randomly Exits Pinball Mode
There is a known issue where the game will appear to exit pinball mode at random (before the ball drains or lands in a saucer) and re-enters video game mode. That may indicate that the diode is reversed on the right flipper switch contacts. The right flipper is different from the left flipper since it is responsible for responding to the player to eject the ball in pinball mode.
Also see the Pinside discussion thread on this issue.
4 Paperwork
Manuals, schematics, coin cards...
5 Modifications
5.1 Pigtail Playfield Adapter
When swapping playfields--especially a lamp socket playfield and lamp board playfield--The playfield connector might not match up with the connector in the cabinet. A pigtail adapter will allow the different playfields to be used without having to modify the original cabling or connectors.
Materials Needed:
- (1) Connector Plug, 15-Pin, 0.084"
- (1) Connector Receptacle, 24-Pin, 0.062"
- (12) Crimp Contact, Socket, 0.062"
- (12) Crimp Contact, Socket, 0.084"
(TODO: Wiring instructions)
5.2 Bezel Lighting
5.3 Lower Playfield Plastics Lighting
6 Service Bulletins
6.1 EOS Switch Wiring Error
6.2 Vidiot & Monitor Adjustments
7 Rubber Rings
Rubber Ring Sizes goes here
8 Photos
Teardown photos go here
9 Repair Logs
Did you do a repair? Log it here as a possible solution for others.