A shorted D2 tries to charge the batteries
D2 only lets current flow from the batteries to U25. If it shorts, the +5 V supply pushes current into the AA cells, which makes them leak onto the CPU board. If it opens, U25 loses its backup.
Systems
Related tips
- New CPU batteries go flat quickly
- Settings lost although the batteries are good (blocking diode D2)
- 'ADJUST FAILURE' every time it powers on: battery corrosion on the CPU board
- "Factory Setting" or "Adjustment Failure" at power-on
- "Factory Setting" or "Adjustment Error" at power-on
- 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
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell