Midway 8080 System Boards
by Mowerman

The Midway 8080 system board was the basis of many of Midway's black & white video games from 1975 till 1980. This board is easy to distinguish because of it's shape, The mother board has a daughter board plugged into it at a 90 degree angle with 2 aluminum braces holding the boards together. (Midway's Omega Race is very similar in appearance but is not part of this system.) The daughter board is used for audio production & amplification and input/output interfacing to the cabinet. The mother board has a 8080 cpu, 16 2708 dynamic Ram chips and 8 sockets for Roms (24 or 28 pin sized). The single edge connector on the mother board is for power input and video output and is double sided ( component side is electrically the same as solder side). There is a strapping section on the motherboard to allow for different configurations of ROM chips by different manufactures.

 The motherboards are nearly functionally identical but come in several basic variations. PC 80-90000-A000 & PC 80-90000-L000 are the last of the series commonly found on Space Invaders and Space Encounters. Revision L000 has 28 pin EPROM socket setup but is used in the 24 pin configuration. The A000 and L000 revision boards also have a 7432 chip near the daughter board connector not found on the earlier boards. Earlier boards I know of are 80-900E, F or H. The layout is slightly different, crystal is in different location & appears that the ROM jumpers may be different. The motherboards are switch able from game to game but the daughter board (Audio, I/O port) is unique to each game, some even have a different board for cocktail vs upright of the same game. Most of the daughter boards can be identified by the circuit board etching with the game name. Some are not as obvious, who would recognize M4 as a game and not a code?

 Sophisticated for it's day it could produce 224 horizontal lines by 256 blocks.

Additional Reading....

• Electronics April 15, 1976
• Standardized Test Procedure for Midway's Processor Boards (MM-1700-1 July, 1976)
• RePlay Magazine September 1976 (Overview & repair tips)
• Repair Tips for Midway 8080 games
• Space Invaders Sound repair tips
  

To activate test, set dips as indicated and hit coin door tilt to start test.

The number under 2716 is the quantity of 2716 EPROM's (or 9316 proms) that should be used on the board.

*1 - Space Invaders did not include a RAM test for Midway 8080 boards since it was licensed from Taito and part of the agreement was no alterations to the code (i.e., test mode).  The Ram Tester P.C. 80-903 can be used to test the RAMs  (from service bulletin 10/10/78).

Note: the original 2716s used on these games were TMS2716's (Texas Instruments) which use 3 voltages and are not compatible with other 2716's.

Space Invaders Cocktails

Game logic boards A084-90700-739 B & C are used in uprights only.

Game logic boards A084-90700-739 D & E can be used in uprights & table models. All jacks are keyed and will plug in properly.

- From Bulletin 3/5/79

Shuffleboard / Space Invaders
[PC 0800-09000 H & K Mother boards]

H is strapped for 2716's Only.
K can be altered for 2716's or 9316's.

-from Bulletin 10/9/78

Space Invaders

Due to a supply problem the 25S10 shifter IC's have been replaced with 74151 Data selector multiplexers.

PC A084-90700-B000 Have (4) 25S10's.
PC A084-90700-C000 Have (8) 74151's.

-from Bulletin 12/11/78

Clowns

Games #101 thru #1439 ROM Letter C/D/E/F/G/H
Games #1439 ROM Letter C2/D2/E2/F2/G2/H2.

Old method of play, new method of play.

-from Bulletin 2/78

Mother Board PC 0080-00-900G

New motherboard has been altered due to the need of additional 16K Prom capability and cannot be used in earlier processor games.  The Extra Innings motherboard is marked 2X & PC 0080-00-900G.

Note: 16K Roms in B, E, F, G, and H. No Roms in C or D.

Games that are not a part of the Midway 8080 system:
Sea Wolf II
Extra Bases
Space Zap
Submarine

Paul Swan
Al Kossow
Tom Wisnionski
Mike Balfour
Chris Hardy
Dick Milikan
The MAME project.

Kev, Mowerman