Fresh batteries die within a short time.
New CPU batteries go flat quickly
Cause: A bad D1 or D2. These two diodes share U25 between the supply and the batteries; if one fails, the cells try to run all the 5 V logic when the game is off, or the supply tries to charge them when it is on.
Fix
- Replace both D1 (1N5817) and D2 (1N4148).
Systems
Related tips
- Battery power not reaching the RAM: diode D2
- Settings lost although the batteries are good (blocking diode D2)
- Settings are lost at power-off even with fresh batteries: bad battery diode D2
- Battery or memory cap won't hold settings
- MPU boots only some of the time
- Cleaning minor battery corrosion on the CPU board before fitting NVRAM
- Testing the MPU reset circuit at U9 pin 40
- Fitting a remote AA battery pack
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell