"Factory Setting" or "Adjustment Error" persists with fresh batteries and a good holder.

Settings lost although the batteries are good (blocking diode D2)

Cause: Blocking diode D2 (1N4148 or 1N914) beside the battery holder is open or shorted, or U25 is bad.

Checks

• Game off, black lead on the backbox ground strap: both sides of D2 should read about 4.2 to 4.8 V, the banded (U25) side about 0.3 to 0.5 V lower.
• Voltage on only the battery side means D2 is open; equal voltage on both sides means it is shorted.
• Check U25 pin 24 (ground is pin 20): about 4.3 V with the game off.
• Diode test: 0.4 to 0.6 one way, no reading the other.

Fix

• Replace D2.
• If all voltages are right, suspect U25 or light corrosion in the holder limiting current.

Systems

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

Related tips

• New CPU batteries go flat quickly
• Battery power not reaching the RAM: diode D2
• Settings are lost at power-off even with fresh batteries: bad battery diode D2
• "Factory Setting" or "Adjustment Error" at power-on
• Check the battery blocking diode D17
• "Factory Setting" or "Adjustment Failure" at power-on
• Test a playfield switch diode
• Spare diodes for coils and switches

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