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!
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