The following documents what is necessary to convert a Gravitar (GRAV),
Space Duel (SD) or Black Widow (BW) to play Major Havoc (MH).
Last Modified: Feb 22 1994
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Get at a minimum the pinouts for the respective games. I'd strongly suggest
you also get a copy of the game wiring diagram (part of the schematics).
Cross check the pinouts below with the wiring diagrams, before powering on.
1. The game board
Atari released Major Havoc in three varieties.
As a dedicated cabinet, similar to that used for I Robot (maybe even the same)
As a conversion for Tempest.
As a conversion for Space Duel, Black Widow and Gravitar.
All three boards should be the same, using a small daughter board containing
4 IC's and labelled "Quad Pokey". If your board is not like this, DO NOT
The two conversions came with a adaptor board. If you have access to the
official Atari SD/BW/GRAV to MH adaptor, you have no need to read this.
If not, you'll have to make your own, so read on.
2. Atari adaptor boards.
The official Atari adaptor board moved X deflection adjustment off the main pcb
and onto the adaptor board (if anyone knows why, please let me know). The
following document will not attempt to do this, X adjustment will remain on the
****** IMPORTANT ******
To allow the X adjustment to take place on the adaptor pcb, Atari cut P19 M/N
from ground, and jumped M/N to the legs of two ICs in the vector generation
If these two jumpers are present on your board, you MUST REMOVE THEM
(desolder both ends, and pull the wire off the board) BEFORE CONTINUING.
If your board, does not have the jumpers, it was probably used in a
dedicated MH cabinet.
If you remove the jumpers, this board will no longer work with an official
Atari adaptor, unless you reconnect the jumpers.
There are probably 1001 ways to make an adaptor, I used the method described
in Rick/Steve's Gravitar2Tempest conversion document, namely:
GAME-HARNESS (P20): PCB:E/C1:wiring:E/C2 :MH-BOARD
GAME-HARNESS (P19): PCB:E/C3:wiring:E/C4 :MH-BOARD
'E/C' are the edge connectors. You will need 4 total (two 24pin [E/C 3,4] and
two 44pin [E/C 1,2]).
'pcb' is a male-to-male .156" spacing board. They are obtainable as '.156"
finger boards' from Louise's Harness Shop (1 800 365 1941) for $2 each.
'wiring' is the crossover wiring used to adapt the signals.
For more details, see the Gravitar2Tempest document.
3. Adapted lines
The two games require much the same signals, just not on the same pins of
the edge connectors. Therefore you need to adapt the signals, this corresponds
to 'wiring' above.
Using different coloured wires, and strong wire at the edges (20 gauge) is a
Remember that the harness numbers below are what is displayed on the harness
edge connectors. The numbers on EC 1,3 will be reversed and should not be
used as a reference.
Line MH Harness
---- -- -------
+5V RTN 1/A 1/A (wire both lines)
+SENSE 21 21
-SENSE 22 22
+5V REG 2/B 2/B (wire both lines)
+22V DC X 3
-22V DC W 4
10.3 UNREG E E
SW GND (UTIL) N N
SW GND (COIN) 12 N
SW GND (CNTL) Z 12
+5V Y Y
TEST F T
COIN L 7 16
COIN R 6 U
COIN AUX K S
CTRL L S H
CTRL R T 6
AUDIO 1 8 12
AUDIO 2 9 11
AUDIO 1 GND 11 M
AUDIO 2 GND M M
RED 4 7
GREEN 6 8
BLUE 8 9
RED GND D H
GREEN GND F J
BLUE GND J K
X OUT 9 A
Y OUT L B
X GND K 1
Y GND 10 2
FIRE L *1 *2
SHIELD P *1 *2
DIR 16 *1
CLR U *1
LIGHT R *3
*1: Wire to the controls of your choice.
I used a Gravitar panel, installed an encoder wheel in place of the <shields>
button, and connected it to wires from <shields> and <thrust> as follows:
Encoder Ground -> <shields> Ground
Encoder +5V -> Jumped from Start2 +5V
Encoder CLR -> <shields>(P19-3)
Encoder DIR -> <thrust>(P19-6)
I connected Fire and Shield to Rotate Left and Right as follows:
Fire(P20-L) -> Rot R(P19-5)
Shield(P20-P) -> Rot L(P19-E)
For Space Duel, pick equivalents.
For Black Widow, you will need to drill at least one extra hole, and
obtain some leaf switches.
*2: Fire and Shield are used to start a game.
Optionally make additional parallel connections to Start1/2
FIRE(P20-L) -> Start1(P20-M)
SHIELD(P20-L) -> Start2(P20-11)
FIRE(P20-L) -> Start(P19-6)
SHIELD(P20-L) -> Select(P20-11)
*3: Start1/Start2 LED's may be wired in parallel to the encoder light.
Be sure to wire a 150 ohm resistor in series on each line.
LIGHT(P20-R) -> (-150ohm->P20-7, -150ohm->P20-J)