Identifying Pinouts on Unidentified Arcade Boards
Written by Rick Schieve



More and more people seem to be catching on to the fact that it is
not all that difficult to get a monitor (with isolation
transformer), a DC power supply, a few controls, and a game logic
board to make an old game work without it's cabinet.  This is a
little tough with vector graphics games like Asteroids but often
very straight forward with raster games.  Let me know if you are
unsure of the difference between vector and raster graphics games
and I'll send you some details.  I also have a past posting in
raster monitor basics I can send.

Video games are often converted to play different video games and
the original logic board set is removed by the machine's operator.
Often you can find the logic board set for a game you really want
(like from Bruce Atkinson's sale or one I may have eventually) but
coming up with documentation is often difficult.  The pinout archive
that Jonathan Deitch puts together may help but you may find
yourself with a logic board and no wiring (often called pinout)
info.  You can often figure it out for yourself on many board sets,
but not all.  The following works for many.

Game logic board inputs include power and control panel inputs.
Outputs include RGB and sync to the monitor plus speaker
connections.

Power inputs to the average game board include +5 for the TTL logic,
usually +12 for sound, and sometimes -5 for certain chips.  Some
boards (like most Pacmans) have AC inputs and do the AC to DC on the
logic board itself but I'm ruling them out for now.

Most board sets will operate with just the +5.  To determine where
to connect the +5 and ground, just find a TTL chip.  14 pin chips
will have +5 on pin 14 and ground on pin 7.  16 pin chips will have
+5 on pin 16 and ground on pin 8.   Either trace some paths or use
an ohmmeter.  Identify all the +5 and ground connections and get a
power supply capable of 6 amps or so at +5 and connect it to the
board.

BTW, make yourself some kind of diagram to fill in to identify the
connections as you go.

The board should hopefully be cycling now.  I use an oscilloscope to
see what is happening now but suspect you could get by with a
voltmeter if you had to.  Anyway, start scoping out the pins you
haven't identified as +5 or ground.  They will fall into several
categories.

First, the control panel switches usually just ground the input of a
TTL gate.  When not grounded by a control panel switch the inputs
are held high by something like a 10K resistor between the input and
the +5 volt supply.  So all pins that weren't directly connected to
the +5 volts to the logic board that are now at +5 are probably
inputs so mark your diagram.

The only active connections at this point will be for the monitor.
Most boards generate a negative composite sync operating at TTL
levels so if you find a connection that looks like TTL signals it
should be the sync.  If there are two your game board uses multiple
syncs and if you don't know how to deal with that I'll send you my
past monitor posting.  Again, most boards will just have one so mark
your diagram with the sync connection.

Assuming this is a color game there will be 3 other active pins that
look about the same.  No relatively clean TTL, but lots of activity
in the 0 to 5 volt range.  These should be the RGB connections to
the monitor.

Power the board down and connect the RGB and sync leads to your game
monitor and turn it on.  You may have the colors wrong but you
should get a picture and you can rearrange the RGB leads until it
looks right.

Occasionally, the game may not come up and you might have to
determine if you need -5 volts somewhere.  This is more difficult as
you really need some device books to see if some of the chips
require -5.  Often just unusual memory components or devices that
keep the high score table working will need the -5.

To identify the inputs, take a clip lead and start grounding the
leads you had identified as inputs.  Eventually you will find the
credit input and once the game has credits you can find the start.
Once you can start a game you can try the other inputs and see what
it takes to move or shoot.  Eventually, you can identify them all
unless the game requires a track ball or a joystick that uses pots.

Last is sound.  Most boards drive a speaker directly while some
need a separate amp.  If there is a pot on the board, there is
usually an audio amp on the board that needs +12 volt to run.  Look
at the as yet unidentified traces at the connector on the board.
The ones with wider traces or that head over towards the pot or a
heat synced chip by the pot will the +12 input.  Often there will be
an electrolytic capacitor across the +12 volts to ground so another
clue is to look for a big cap with a rating of at least 12VDC.

When you think you have the +12 input attach a +12 volt supply good
for an amp or so and power everything up and start a game.  Now look
for some activity on leads that were not active before.  Chances are
you can attach a speaker between the pin you find and ground and
sounds will come out :-)

You should pretty well have everything identified now.  Again, there
are lots of exceptions for differences like multiple syncs, special
voltage requirements, separate audio amps, or special input devices,
but in my experience about 80% of the logic boards I've fooled with
can be made to work as I've described.

Any other suggestions would be appreciated, but no flames please as
I burn easily ;-)

                               Rick Schieve