Replacing batteries with a gold cap

Williams games since 1979 have had a nuisance: the three AA batteries must be replaced once in a year or two. Old batteries may leak and destroy the circuit board. By using alkaline batteries, you may reduce risk of leaking, but what if next time you replace the batteries it would be the last time? Just replace the batteries with a gold cap!

Gold cap installed on WPC CPU board

The gold capacitor is easy to install onto WPC CPU board. The negative terminal of cap connects to a thru hole near D1 diodes cathode end. Positive terminal is connected via a 180 ohm (value is not critical) resistor to cathode of D1. The resistor limits capacitor charging current when it is empty. The capacitor is secured in place with some hot melt glue or silicone rubber.

Gold cap installed on System 6 CPU board

Capacitors negative terminal again goes to ground, the positive terminal is connected via resistor to cathode of D18.

The capacitor keeps bookkeeping and game settings intact for at least two weeks. It is charged by keeping the game turned on for a few minutes. Goodbye battery replacing, so long for the leaky nicads! The capacitors can be found in all good component stores. In older games, a 0.47 F capacitor is sufficient, but in WPC games the current demand is bigger because of WPC ASIC, so I recommend a 2.2 F capacitor there.

Note there are two kinds of backup capacitors, one type is for large currents and has greater leakage current and is thus not very good for long term backup. The other is for low current use and has very small leakage, and that type is good in pinball games. For example, Tokin's capacitors of type FS and FA are for large currents, and FY is the long life small current type.

There are differences in current consumption between games. CMOS RAM in stanby may require only 1 microamp, but some chips may take 10 uA. It varies from game to game how long the capacitor actually holds the memory, or memory and clock in newer games. After installing the cap, you should keep the game on for a few hours to let the capacitor fully charge for the first time. An unused capacitor takes longer to charge, because the isolating layers inside the cap are not yet fully formed.

Leaky battery from a Bally board has been replaced with a gold cap.

Changing to gold cap is also an ecological thing to do. There will be no more troublesome battery waste from your game. You can also replace the nicad battery in Gottlieb or bally games with a gold cap. The capacitor is connected directly in place of the old battery. Take care to dispose of the old battery properly!