Converting Galaxian to Pacman PCB Mod
July 2, 1997
This document covers the following hacks:
for a 36k ZIP file of all the ROM images needed for these
These images are thanks to Dave Grohowski.
The hack is thanks to Dave and Patrick Peters.
Note the combination ROM files were created by concatenating the
original ROM files using the following MSDOS copy command with the "/b"
copy /b rom1+rom2+rom3+rom4+rom5 allroms
Galaxian to Pacman pcb Modification
This document describes how to take a Midway Galaxian PCB (printed
circuitry board) and convert it to run Pacman. After this mod, the
modified Galaxian pcb can be inserted directly into a Pacman cabinet and
This mod changes the pcb to use a single 27128 EPROM instead of five
2716 EPROMs that live on the satellite PCB. This should increase the
reliability of the PCB as there are fewer chips, and the satellite board
can be discarded.
This procedure also uses 2732 EPROMs at locations 1K and 1H (the
equivalent of row 5 on a Pacman board, which are the character ROMs).
Through-out this procedure, the pcb is always positioned with the edge
connect towards the ceiling. All modifications are done to the component
side of the pcb unless otherwise stated.
- wire wrap wire
- (1) 28 pin socket.
- (1) 27128 EPROM.
- (2) 2732 EPROMs.
- EPROM images. GALPAC7F.128 is the position 7F chip 27128
EPROM file for the modified version of Pacman (no it is not the
standard Midway Pacman ROM code). GALPAC7F.256 is the position 7F
chip 27256 EPROM file that includes both the modified Pacman and
original Galaxian ROM code. GALPAC1H.732 is the position 1H chip
2732 character EPROM file. GALPAC1K.732 is the position 1K chip
2732 character EPROM. These character ROMs files are quite a bit
different than the standard Pacman 5E and 5F ROM code. If someone can
figure out how these two EPROMs are addressed, maybe the standard Pacman
character ROMs could be re-organized and used instead of these funky
PCB Modification steps.
- On the solder side, cut the traces going to the top edge
connector parts side pins 6 and 7 (on the solder side, the pins
are counted right to left). Also cut traces going to both the
solder and component sides for the edge connector pin 18.
- Tie solder side pin 18 and component side pin 18 to
edge connector parts side pins 6 and 7. This converts the
Galaxian speaker pins to Pacman. Note all other pins are the same for
- Remove the original Galaxian satellite board from sockets 7F and 7L.
This board holds the five 24 pin 2716 EPROMs (or ROMs) in positions 7U,
7V, 7W, 7Y, 7Z.
- Bend out the following leads on a 28-pin DIP socket: 1, 2, 20, 22,
23, 26, 27, 28.
- Install the socket into the Galaxian main logic board at location 7F
(the right most socket, as facing the PCB with the edge connector
towards the ceiling, that held the satellite board), aligning the
inserted socket pin 14 with PCB socket pin 12. Pins 1, 2, 27, 28 will
hang over and not plug into the PCB socket.
- Connect pins 1, 27 and 28 together with wire-wrap wire, leaving
about 1" connected to the socket. Connect the attached wire hanging from
pins 1, 27, 28 to +5 volts on the logic PCB. This is best connected at
location 7J pin 24 (where there is no socket or chip).
- Connect the remaining pins on the new socket with wire-wrap wire as
- 1) Tie Pin 2 (A12) to chip 7D Pin 5.
- 2) Tie Pin 20 (CE) to Ground (best connected at location 7J pin
- 3) Tie Pin 22 (OE) to chip 8E pin 13.
- 4) Tie Pin 23 (A11) to chip 7D Pin 3.
- 5) Tie Pin 26 (A13) to chip 7D Pin 7.
If you want to use a 27256 EPROM instead (and have both Pacman and
Galaxian ROM code loaded), you can add these steps. This made
diagnostics much easier when developing this hack because I could
instantly switch back to the original Galaxian ROM code to diagnose a
- 6)* Tie Pin 27 (A14) to the center pin of a SPDT switch.
- 7)* Tie one outside pin of the SPDT switch to ground.
- 8)* Tie the other outside pin of the SPDT switch to +5 volts.
* additional steps for using a 27256 EPROM.
- Using a de-soldering tool, remove the TTL chip at location 9N (a
74LS259). Install a 16 pin socket in it's place. Straighten and clean
the pins on this chip (do not discard).
- Take the 74LS259 removed above, and bend pins 11 and 12 out so they
will not contact the socket. Insert the chip into the installed socket
with pins 11 and 12 sticking out and "hanging in the wind".
- On the solder side of the pcb at chip location 9N, tie pins
11 and 12 together, and then tie them both to ground. In this step you
are grounding the pcb pins, not the chip pins. (the above 3 steps
that modify location 9N turn the monitor so the game doesn't play upside
down in a cocktail cabinet).
- On the solder side of the pcb at chip locations 1K and 1H, cut the
thick trace connecting to pin 21 (top row, 4th pin from the right). The
tie 1K and 1H pins 21 together, and then to chip 2F pin 1 (which is the
bottom left pin on the solder side). Even though Galaxians is already
set up to use 2732 or 2716 EPROMs at locations 1K and 1H, this step is
necessary to address the character ROM space correctly.
- (this step not necessary; I don't know what it does but it was used
on a hack Dave examined). On the parts side at chip location 8E pin 14,
lift or cut this pin from the pcb. Then connect the disconnected pin of
the chip to ground.
- The game requires two coins to get a single credit.
- In a cocktail game player 2 does not flip.
Things to think about and work on
- The up joystick (Galaxian Fire button) does not work. Left,
right and down work, but UP does not work.
- How could the chip mods be reversed so we could switch easily back
and forth between Pacman and Galaxians? I am currently using a 27256
EPROM with both Pacman and Galaxian ROM code to test and modify the
above hack. But the other board mods would have to be turned off too to
make using a 27256 with both games feasible.
- To do the above, we would have to use a 2764 at position 1H and
switch between the two character ROM code sets. Position 1K could stay
with the 2732 Pacman character ROM. As a middle step, Galaxians would
have to work with a single 2732 character ROM at position 1H.
Converting Galaxian to run both Galaxian and Pacman.
I am testing hack1 using
a 27256 EPROM and switching back and forth between the Pacman and Galaxian
ROM code. It works, but as described above, there are several things that
need to be worked out. I'll keep you posted.
Galaxian PCB Pinout and using Galaxian in a Pacman Cabinet.
Power supply: Galaxian gets its input voltages from a 7 volt/12 volt AC
transformer. Once this power is on the pcb, it is converted to 5 volts DC
and 12 volts DC (essentially the power supply is built-in to the logic
BUT you can hook up a standard switching power supply, which supplies 5
volts DC at 7amps (or greater), and 12 volts DC to the Galaxian 7 volt AC
and 12 volt AC input lines. This causes no problems. My only suggestion is
that you turn the 5 volt adjuster all the way up on the switching
power supply. This will make the output voltage from the switcher close to
6 volts. The Galaxian logic board will draw this voltage down to 5 volts.
Galaxian vs. Pacman
You CAN play Galaxian in your
Pacman/Ms.Pacman cabinet! The only difference in PCB pinout is the
speaker. Even the joystick works correctly; left is left, right is right,
and UP is FIRE. The power supply section is the same (both use a AC
transformer to supply +7 volts AC and +12 volts AC).
I modified my Galaxian PCB so the speaker is (component side) pins F
and H (like on Pacman) instead of pins V and 18. This way I can just flip
my Galaxian board into my Pacman cabinet when I want to play.
Note: If you hacked your Pacman wiring and used a Regulated power
supply to supply pin 18 with +5 volts DC, do not install your
Galaxian board! If you are using a regulated power supply, wire it
conventionally to the +7 volt DC pins. It will work fine in this manner!
wire | wire
Pin Componet side color | Pin Solder Side color
--- ------------- ----- | --- ----------- -----
A GND (center tap 7v) | 1 GND (center tap 7v)
B GND (center tap 7v) | 2 GND (center tap 7v)
C +7 volt AC | 3 +7 volt AC
D +7 volt AC | 4 +7 volt AC
E Key (7.5 vdc out) | 5 Coin Meter in
F (Pacman speaker) | 6 reset
H (Pacman speaker) | 7 Coin Meter out
J Coin mech switch | 8
K Test switch | 9 Credit switch
L Select one player | 10 Select two player
M P1 move left | 11 P1 move right
N P1 Fire | 12 P2 Fire
P P2 move left | 13 P2 move right
R to GND for cocktail | 14
S GND for RGB | 15 GND for controls
T RGB Red | 16 RGB Green
U RGB Blue | 17 RGB Neg Sync
V Galaxian Speaker | 18 Galaxian Speaker
W +12 Volt AC | 19 +12 volt AC
X +12 Volt AC | 20 +12 volt AC
Y GND (center tap 12v) | 21 GND (center tap 12v)
Z GND (center tap 12v) | 22 GND (center tap 12v)