MPU Battery Replacement Options

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1 Introduction

RAM chips are typically used to store game settings and bookkeeping data. However, RAM is volatile and can only store data if power is applied to the chip. If power is lost, so is the data. So, the solution to this was to include a battery on the MPU to retain the data in RAM when the game was turned off.

Unfortunately, many of these batteries leak and damage or destroy circuit boards in the process. So, it is imperative that the battery is removed from the MPU in order to prevent this damage in the future.

In order to retain the data for game settings and bookkeeping, there are a few different options to replace the original battery and prevent future problems from leakage.

This guide assumes that the old battery has already been removed from the MPU and any damaged caused by a leaking battery has been cleaned up and repaired.

1.1 Remote Battery Pack

The remote battery solution is when a battery pack is installed in a game, but lead wires are attached to the positive and negative solder points on the MPU.

Battery pack installed on a Gottlieb Genesis. User failed to install a blocking diode. Pic courtesy of Ray Brackins at Wide Area Repair

On older game systems that originally had a rechargeable battery installed, a diode must also be installed to prevent the MPU from attempting to charge the non-rechargeable batteries (referred to as a "blocking diode"), otherwise the batteries may expand, leak, and/or explode.

The safest place to mount a remote battery pack is below any circuit boards and as far away from them as possible, so as to avoid escaping gas and drippings from leaks. It has been reported that circuit boards have been affected by the gas from leaking batteries as far as 6 inches away.

Additionally, it can be a good idea to put the battery pack inside a zip lock bag to help limit damage from a leaking battery.

1.2 Lithium Battery

Classic Williams games had a build-in battery holder that could fit AA batteries. Unfortunately, it was common to see standard alkaline batteries used in these holders, which always leaked.

Lithium batteries are produced in the AA battery footprint, so can be installed in the battery holders used on classic Williams MPUs. Lithium batteries are less prone to leaking, but it is still a good idea to mount them off the MPU in a remote battery pack.

Installing batteries directly onto the MPU leaves the game open to the possibility of an owner replacing a dead AA lithium battery with a AA alkaline battery if they don't have a lithium battery on-hand because it's the easy and lazy thing to do. As a result, battery leakage becomes a serious risk again.

1.3 Memory Capacitor

Memory capacitors are special capacitors that hold a charge for an extended period of time and take the place of a battery. The downside is that the game has to be turned on at least once for several hours every 14-30 days in order to build up to a full charge.

Note that on some game systems, a resistor with a higher resistance and/or wattage must be installed in order to handle the inrush of current, especially since a depleted memory capacitor can briefly act as a dead short.

Note that on games systems with a real-time clock, a memory capacitor will only last a few days, since energy is being drained by both the clock and the RAM.

Additionally, lower quality capacitors are prone to leaking, though not as spectacularly as alkaline or NiCad batteries, so it is important to stick with a reputable brand.

At this point, memory capacitors have fallen from favor because of only holding a short-term charge, as well as the introduction and economical prices of lithium batteries, lithium coin cell batteries, and NVRAM.

1.4 Coin Cell / Button Battery

Lithium coin cell batteries (also known as button batteries) are much less prone to leakage than the batteries originally used on MPUs. They typically have about a 10-year life span when used on an MPU. Gottlieb System 3 MPUs were the first to utilize coin cell batteries.

On older game systems that originally had a rechargeable battery installed, a diode must also be installed to prevent the MPU from attempting to charge the non-rechargeable lithium battery (referred to as a "blocking diode"), otherwise the battery may expand, leak, and/or explode.

Note that through normal usage, the risk of a lithium battery leaking is pretty small, but they still can--and do--leak after enough time. Poor storage conditions are also sometimes a contributing factor.

Gottlieb System 3 MPU with a leaking coin cell battery

1.5 NVRAM

NVRAM (non-volitile RAM) is being used to replace volatile RAM installed on the MPU. Volatile RAM can only store data if power is applied to the chip. If power is lost, so is the data. NVRAM can retain data without needing any power. It is essentially "frozen" in the chip.

Various game systems use different types of RAM, so adapters are needed to adapt the footprint and pinout of the 6264 NVRAM pinout to the RAM footprint/socket that the game system is using.

NVRAM adapters typically list which RAM footprints/sockets and/or game systems they are intended to support.

1.5.1 Products

Most NVRAM developers sell directly on their websites, but some are also available from various pinball suppliers.

• AnyPin Adapter (Pinball Life)
• Pinitech Adapters
• Pinball Electronics Adapters (barakandl)
• Pinball Electronics

2 Game Systems

2.1 Allied Leisure

2.1.1 Generation 1

Game data is not saved. A battery solution is not necessary.

2.2 Alvin G

• Remote Battery

2.3 Atari

2.3.1 Generation 1

Game data is not saved. A battery solution is not necessary.

2.3.2 Generation 2

• Remote battery
• Coin cell battery
• Memory capacitor

Note: Generation 2 games generally suffer no ill effects when running without a battery, other than that high scores and bookkeeping data would not be retained.

2.4 Bally

2.4.1 -17/-35/-133 MPU

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

Note: running some classic Bally games without a battery or battery replacement will cause the game to play default sounds, and not the correct sounds for the game. This affects games like Xenon, Eight Ball Deluxe, Flash Gordon, Skateball, Centaur, Cybernaut, and Fathom.

2.4.2 6803 MPU

• Remote Battery
• NVRAM

2.5 Capcom

• NVRAM

2.6 Data East

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

2.7 GamePlan

• Remote Battery
• NVRAM (not fully tested)

2.8 Gottlieb

2.8.1 System 1

• Remote Battery
• Coin Cell Battery
• NVRAM

Note: Running without a battery attached can sometimes introduce garbage data for the high scores and bookeeping data at power up.

2.8.2 System 80/80A/80B

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

2.8.3 System 3

• Remote Battery
• Coin Cell Battery
• NVRAM

NVRAM installed with jumpers pictured on a Gottlieb System 3 MPU

Some experimentation leading to the development of an NVRAM solution can be found here.

Note: Operating the game with no battery or a failing battery will display the message "low battery or bad U3 or U6". To bypass this error message, press the reset button (SW1) on the MPU.

2.10 Jersey Jack Pinball

• A coin cell battery is installed on the motherboard.

2.11 Sega

• Remote Battery
• Coin Cell Battery
• Memory capacitor
• NVRAM

2.13 Stern

2.13.1 MPU-100/MPU-200

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

Note: The MPU-200 uses two RAM chips and has two RAM sockets. Two separate 5101 adapters can be used, or an adapter that specifically accommodates this board can be used.

2.13.2 Whitestar

• Remote Battery
• Coin Cell Battery
• Memory capacitor
• NVRAM

2.13.3 SAM

• Remote Battery
• Coin Cell Battery
• NVRAM

2.13.4 SPIKE

• A coin cell battery is mounted vertically on the PCB in the backbox.

2.14 Williams

2.14.1 System 3-7

• Remote Battery
• Memory Capacitor. Alternate guide.
• Coin Cell Battery
• NVRAM

2.14.2 System 9

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

2.14.3 System 11/11A/11B/11C

• Remote Battery
• Memory Capacitor
• Coin Cell Battery
• NVRAM

2.14.4 WPC

• Remote Battery
• Remote Battery on WPC-95
• Coin Cell Battery
• NVRAM

Note: Games that utilize a real-time clock will need a battery instead of NVRAM to keep proper time. Otherwise, the date/time will not advance while the game is powered off.

2.14.4.1 Games Affected By a Real-Time Clock

WPC (Fliptronics II)

• Creature from the Black Lagoon (different music plays based on the date)
• Twilight Zone (clock on the playfield shows correct time)

WPC-S

• Dirty Harry (midnight madness)
• Johnny Mnemonic (midnight madness)
• WHO dunnit (midnight madness)
• Theatre of Magic ("hermaphrodite position" - midnight madness does not depend on real time clock since it is a game mode)

WPC-95

• Congo (midnight madness)
• Junk Yard (midnight madness)
• NBA Fastbreak (midnight madness)
• Medieval Madness (midnight madness, but special mode needs to be enabled to activate it)

Note that on games systems with a real-time clock, a memory capacitor will keep the clock going, but since energy will be drained by both the RAM and the clock, a fully charged memory capacitor is reported to be able to keep the clock active for about 2-4 days, while the RAM will lose its settings after about 10 days. Additionally, on WPC systems, a minimum of 3v is required to keep the real-time clock alive, while the RAM can sometimes be kept alive until the memory capacitor has drained to as low as 2v with 6264 RAM and 1v with 5101 RAM.

2.14.5 Pin2000

• Coin Cell Battery

2.15 Zaccaria

2.15.2 Generation 1

• Battery or Memory Capacitor
• NVRAM

2.15.3 Generation 2

• Battery or Memory Capacitor
• NVRAM