Checking the battery holder voltages on the CPU board

Steps

• Turn the game off.
• Meter on DC volts, black lead on the ground strap or a CPU board mounting screw.
• Touch the red lead to each battery positive solder point on the CPU board in turn.
• Expect about 1.5, 3.0 and 4.5 V as the cells add up along the chain.
• Missing steps mean corroded holder terminals; replace the holder and re-test.

Systems

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

Related tips

• Better battery holder for System 11 CPU boards
• Fitting a remote battery holder
• Changing the CPU batteries without losing settings
• 'ADJUST FAILURE' every time it powers on: battery corrosion on the CPU board
• New CPU batteries go flat quickly
• Settings lost although the batteries are good (blocking diode D2)
• "Factory Setting" or "Adjustment Failure" at power-on
• A shorted D2 tries to charge the batteries

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