Changing the CPU batteries without losing settings

Steps

• Remove the backglass to reach the CPU board, then turn the game on.
• Note which way the batteries face, then remove them.
• Clean any corrosion on the holder contacts with 220 grit sandpaper; if the holder is damaged, turn off and replace it.
• Write the date on the new batteries, fit them, then turn the game off.
• Fitting batteries with the power on keeps the settings and audits. Change them every year, two at most.

The backbox is live with the game on; touch only the batteries and holder.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Changing batteries without losing settings
• New CPU batteries go flat quickly
• 'ADJUST FAILURE' every time it powers on: battery corrosion on the CPU board
• Settings lost although the batteries are good (blocking diode D2)
• Checking the battery holder voltages on the CPU board
• Cleaning up battery leakage on the CPU board
• Better battery holder for System 11 CPU boards
• "Factory Setting" or "Adjustment Failure" at power-on

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell