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Bally AS-2518-17 MPU Board Modification for EPROM Chips
(Also applies directly to Stern MPU-100 Boards)
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Many of the Technical Articles on our site contain information and directions involving electronics and circuit board repair. They are authored with the assumption that the reader has adequate experience and knowledge required to do the work being described.

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This article discusses modifications and jumper changes required in order to run 2716 or 2732 EPROM chips on your Bally AS-2518-17 or Stern MPU-100 MPU board.

IMPORTANT NOTES:
The Bally AS-2518-17 and Stern MPU-100 boards can be used to run ONLY the following games:
Bally:Freedom, Night Rider, Evel Knievel, Power Play, Mata Hari, Black Jack, Strikes and Spares, Eight Ball
Stern:Stingray, Pinball, Stars, Memory Lane, Lectronamo, Nugent, Dracula, Wild Fyre, Trident, Hot Hand, Magic
Later Bally AS-2518-35 and AS-2518-133 MPU boards will run any of the above games, as well as the later games, but if your game is not listed above (ie: you have a newer, or later model game), you will need to use the AS-2518-35 or AS-2518-133 MPU board- the AS-2518-17 board will not work properly with later games.

If you need a replacement MPU board, several new aftermarket replacement boards are available ranging from $200 to $350 in cost. E-mail us if you need further details.

Early Bally AS-2518-17 and Stern MPU-100 boards (1977- early 1979) were designed to work only with the original masked ROM chips that came on them from the factory, and not with replacement EPROM chips that we use now. ROM chips were cheaper to manufacture in quantity at the time, and replacements weren't a consideration then.

If you have an original board and are replacing the original 9316A PROM chips on it with EPROM chips, you will need to verify/change some jumper settings, and do some modifications to the circuitry on the board. The modifications aren't too complicated, as long as you are careful, patient, and comfortable working with soldering tools and circuit boards in general. If you are not, then trust the work to someone who is competent- you may thank yourself later.

Using 2716 EPROM Chips:

When using 2716 EPROM chips in locations U2 and U6, make the following jumper changes:
  1. Jumper E1-E2
  2. Jumper E6-E7
  3. Jumper E3-E4
All other jumpers should be left as-is (assuming they have been unmodified and are "factory original").

Then make the following modifications to the board:

Cleanest way:
Solder side of board:
  1. Cut trace leaving pin 4 of U18.
  2. Solder the part of this trace that is no longer connected to U18, to U18 pin 5. (Basically re-route the trace from pin 4 to pin 5).
  3. Cut the trace at Pin 21 on both U2 & U6.
  4. Run a jumper from Pin 21 over to Pin 24 on both.
Messier way:
Component side of board:
  1. Cut pin 4 away from U18
  2. Flip board over (all further mods are on solder side of board)
  3. Short pin 4 to pin 5 on U18 with a solder blob.
  4. Cut the trace at Pin 21 on both U2 & U6.
  5. Run a jumper from Pin 21 to Pin 24 on both.



Using 2732 EPROM Chips:

When using 2732 EPROM chips in locations U2 and U6, make the following jumper changes:
  1. Jumper E1-E2.
  2. Jumper E6-E7.
  3. Jumper E3-E4.
All other jumpers should be left as-is (assuming they have been unmodified and are "factory original").

Then make the following modifications to the board:
  1. Cut trace leaving U18 pin 4, on SOLDER side of board:


  2. Connect part of trace not connected to U18 pin 4, to U18 pin 5.

  3. Cut trace leaving U2 pin 21 on SOLDER side of board:


  4. Cut trace leaving U6 pin 21 on SOLDER side of board:


  5. Make a three way connection between U2 pin 21, U6 pin 21, and U9 pin 24.


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