Replacement MPU Board for Bally (1977-1985): Which One to Choose?
Your Bally (1977-1985) pinball machine won't start, or the battery has leaked on the MPU board? This is the classic failure of this generation. The lasting solution: replace the original MPU board (AS-2518-17/35/133, Stern MPU-100/200) with a modern, battery-free board. This guide explains how to choose.
What Is a Replacement MPU Board?
The MPU (Micro Processor Unit) is the brain of the pinball machine. On Bally "-35" machines, it uses a battery that eventually leaks and corrodes the board. A modern replacement MPU board serves the same purpose without a battery, in a Plug & Play format, permanently eliminating the risk of corrosion.
Key Selection Criteria
- Compatibility: does it properly replace the AS-2518-17/35/133 and Stern MPU-100/200 boards?
- Gameplay fidelity: does it run the original ROMs, or does it use reprogrammed games?
- Battery-free: no more corrosion.
- Freeplay.
- Repairability & support: can it be easily serviced, with accessible support?
Our Recommendation: the BallyFA
The BallyFA replaces the original MPU board in Bally (1977-1985) pinball machines, including Bell Games models. It runs the original ROMs directly in its FPGA (gameplay faithful to the original era), operates without a battery (no more corrosion), and installs as Plug & Play.
What if something goes wrong? The fusible components (the ones most likely to fail) are mounted in sockets: replacement requires no soldering, just a few seconds. We also provide repair tutorials and free technical support. No disposable boards here.
Configuration: Dip Switch Settings
The BallyFA is configured simply via two blocks of dip switches — a real asset for installation and troubleshooting.
S1 — Game Selection
The S1 block selects the game the BallyFA will run, based on the ROMs stored on the SD card (see the complete game list in the manual).
S2 — Options (default: all OFF)
- S2-Dip1 — Zero Cross Emulator: Bally MPU boards require a “Zero Cross” signal (from the 12V power supply) to operate, which is checked at startup. When set to ON, the BallyFA emulates this signal — useful for bench testing with a simple 5V power supply (timing differs with the emulated zero cross).
- S2-Dip2 — NVRAM to EEPROM Backup: the BallyFA saves NVRAM contents (high scores, extended settings) to an EEPROM, with each game having its own zone. On the bench, briefly switching Dip2 to ON forces a save. During normal play, saving is automatic (test button, end-of-game relay, credit button).
- S2-Dip3 — Not used (reserved, not yet implemented).
- S2-Dip4 — Anti-flicker (LEDs): when set to ON, the BallyFA adjusts the Zero Cross timing for flicker-free LEDs, without needing to add a parallel resistor on each LED (a known issue on Bally machines).
- S2-Dip5 — Coin validator: when set to ON, enables the coin validator. Do not enable if no coin validator is connected.
- S2-Dip6 — NVRAM Initialization: when set to ON, the BallyFA initializes (resets) the NVRAM for the selected game at startup — useful for fully resetting the RAM.
What About Other Solutions?
The Alltek Ultimate MPU is the leading American market reference: an excellent board that replaces Bally (1977-1985) MPU boards, featuring 90+ games on a chip (selected by dip switches), Freeplay, self-test, and an auto-resettable fuse. Its logic is based on reprogrammed PROMs. The BallyFA takes a different approach: it runs original ROMs on an FPGA (hardware-level fidelity), and focuses on repairability (socketed components) plus technical support. The right choice depends on your priorities.
Comparison
| Criteria | BallyFA | Alltek Ultimate MPU |
|---|---|---|
| Replaces | Bally (1977-1985) MPU | Bally (1977-1985) MPU |
| Battery-free | Yes | Yes |
| Game logic | Original ROMs interpreted (FPGA) | Reprogrammed PROMs (90+ games, dip switches) |
| Freeplay | Yes | Yes |
| Configuration | Dip switches: game selection, Zero Cross emulator, LED anti-flicker, coin validator, NVRAM backup/initialization | Dip switches: game selection, Freeplay |
| Repairability & support | Socketed fusible components + tutorials + support | Self-test + auto-resettable fuse |
FAQ: Bally (1977-1985) Replacement MPU Board
What boards does the BallyFA replace?
The original MPU board in Bally (1977-1985) pinball machines, including Bell Games models.
Is there a battery to replace?
No. The BallyFA operates without a battery: no risk of corrosion whatsoever.
Does it run original ROMs?
Yes, it interprets the original ROMs in its FPGA, for gameplay faithful to the original.
Can it be configured (game, LEDs, coin validator...)?
Yes, via dip switches: game selection (S1) and S2 options (Zero Cross emulator for bench testing, LED anti-flicker, coin validator, NVRAM backup/initialization).
Is it repairable?
Yes. Its fusible components are mounted in sockets (no-solder replacement), with repair tutorials and free technical support included.
Not sure about your model? Contact us — support is included.
