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Bally & Stern General Game ROM Chip & Jumper Info
NOTICE: For some very important information, please read the Technical Article Notice and Disclaimer, found on our Technical Articles Index page before performing any of the work described below. The information given below assumes you have read the Notice and Disclaimer first.

The guide below is intended as a basic introduction to the process of changing ROM chips on the MPU board of your Bally or Stern pinball machine. It is designed to familliarize you with the terms of the parts and steps involved, and help you to get an idea of what may be required to replace or install new ROM chips on your board.

Information in this article applies to Bally MPU board models AS-2518-17, AS-2518-35, AS-2518-133, and Stern MPU boards MPU-100, and MPU-200. See the following section on Determining What MPU Board You Have to determine which board your game has in it.

This article does not go into great technical detail, and is not a guide for ROM chip replacement itself, but is intended to simply introduce you to what may be required in order to properly change ROM chips on your board.

HELP! If you're attempting a ROM chip replacement in your game, and find that the information in this article is "over your head", it may be best for you to leave the technical work to a qualified repair person. See our Game Service & Repair page for a list of repair sources.

  • For information on purchasing replacement ROM chips for your game, Click here.
  • More technically-oriented information can be found in other articles on our Technical Articles page.
  • Click here for details on modifications and jumper settings for Bally AS-2518-17 and Stern MPU-100 boards.
  • Click here for details and jumper settings for Bally AS-2518-35 and Bally AS-2518-133 boards.
This article contains the following sections:

Brief Overview of Changing ROM Chips:

When changing ROM chips on your Bally or Stern MPU board, you will need to complete the following steps:
  1. Determine what type of MPU board you have. Click here
  2. Determine what type of chips you are installing. Click here
  3. Determine whether or not your board is configured for the chips you are installing. Click here
  4. Make any necessary changes to your board, for the types of chips you are installing.
Each of these steps is described below.

Determining What MPU Board You Have:

Both Bally and Stern boards had their board ID number printed in the lower right corner of the MPU board, in white ink. Sometimes labels or stickers were put over the number, so you may need to remove a sticker or two to find the number.

For Bally boards, you should find "AS-2518-17", or "AS-2518-35".

On Stern boards, you should find "MPU-100" or "MPU-200".

The type of board your game has will determine what needs to be done to it in order to replace ROM chips.

These boards were used in Bally and Stern games, respectively, from 1977 through 1984/1985. ROM chip locations on these boards are labeled U1, U2, U3, U4, U5, and U6. Note that not all boards use chips in all of these locations- most games only use two or three chips, but it can vary from game to game.

Replacement ROM Chips:

When installing new ROM chips on your Bally or Stern MPU board, you will need to determine what kind of chips you are installing. Once you know what kind of chips you are installing, you can then determine if your board is properly configured for those types of chips. If it isn't, you can make some changes to the board so that it will work with the chips you are installing (described below).

Most replacement ROM chips for Bally and Stern MPU boards are "EPROM" type chips. An EPROM chip is a chip that can be erased and reprogrammed.

Many original (factory) ROM chips for Bally and Stern MPU boards are "PROM" type chips. A PROM chip is a chip that cannot be erased and reprogrammed.

Some boards even came from the factory with a combination of EPROM and PROM chips installed.

EPROM and PROM chips are not always interchangeable.

You will need to determine what types of chips you are installing on your board. All chips should have some numbers printed on them which will help identify what kind of chips they are. Look for the following numbers on your chips:
  • PROM Chips: 9316, 9316A, 9322
  • EPROM Chips: 2516, 2716, 2532, 2732
Once you have identified the types of chips you are installing, you can proceed to the next step, which is determining if your board is properly configured for the types of chips you are installing.

Configuring Your MPU Board for New ROM Chips:

Since several different types of ROM chips can be used on Bally and Stern MPU boards, the designers of these boards engineered a handy way of "configuring" or "setting up" the board for the types of chips being used.

These boards use "jumpers", which can be moved, or reconfigured, depending on the type of ROM chips being used. A jumper is basically just a piece of wire (often bare wire) which connects two points on the board. Changing a jumper basically means desoldering one end from one point, and connecting that end to another point.

On Bally and Stern boards, the jumper points are labeled with the prefix "E". For example, jumper #1 is labeled "E1", and jumper #20 is labeled E20.

Some jumpers also have "sub jumpers" that have an "A" prefix on them. For example, your board may have a jumper E16, and another jumper E16A.

Here is a picture of two jumper locations on a late-model pinball MPU board- W1 and W2. (Late model boards use "W" for their prefix instead of "E", and use what look like resistors instead of bare wire, for the jumpers):


Or, more clearly:


A jumper connection between either set of two points is considered "IN", or "set". A set of two points that doesn't have a connection between them, is considered "OUT", or "not set".

Jumpers will have to be set according to the type of ROM chips you are installing. This is where the process gets technical. To change jumper settings, you'll need a soldering iron, some solder, de-soldering wick (or "braid"), or a de-soldering tool, and possibly a small piece of wire to use as a jumper.

Use care when desoldering and soldering on these fragile circuit boards- too much heat from a soldering iron can lift solder pads and traces, and can damage the board. Excess solder can short the jumper to other connections nearby.

Important Note: If you're uncomfortable doing this kind of work, we strongly recommend leaving it to someone who is experienced. If you don't have experience working electronic circuit boards, it can be too easy to make a mistake, or damage something beyond repair. It's better to send the board out to have the work done, rather than risk damaging it yourself.

Jumpers must be configured properly for the type of ROM chips being installed. If the board is not configured properly, then it will not work!

More Info:

Early Bally/Stern MPU Boards - Configuration Details:

Bally AS-2518-17 and Stern MPU-100 boards will not only need jumper configuration, but will also need to have some physical modifications done to the board in order for it to use EPROM chips.

These early boards were designed strictly for PROM chips only, so in order to use the newer style EPROM chips, they must be physically modified, or "altered" in order to work properly with EPROM chips.

Bally games that used the early "-17" board were: Freedom, Evel Knievel, Night Rider, Eight Ball, Power Play, Mata Hari, Black Jack, and Strikes & Spares.

Stern games that used the early "MPU-100" board were: Pinball, Stingray, Stars, Memory Lane, Lectronamo, Wild Fyre, Ted Nugent, Dracula, Trident, Hot Hand, Magic, and Cosmic Princess.

Click here for information on jumper changes and the modifications required for Bally AS-2518-17 and Stern MPU-100 MPU boards.

Late Bally/Stern MPU Boards - Configuration Details:

Bally AS-2518-35, AS-2518-133, and Stern MPU-200 boards will require only jumper changes to configure them for the particular type of ROM chip you are installing. No board modifications are necessary.

Click here for information on jumper changes required for Bally AS-2518-35 MPU boards.


The above information should be enough to familliarize you with what is required for installing new ROM chips on your particular MPU board.

  • If you require more in-depth technical information, please see the other articles available on our Technical Articles page.
  • If you would like to find a qualified repair shop to configure your MPU board for you, see our Game Service & Repair page.
  • If you are searching for replacement ROM chips, see our ROM Chips page.

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