Run a System 6/7 CPU board on +5 V only
Steps
- First try the board without the unregulated supply on 1J2 pin 9.
- If it will not run, jumper +5 V from capacitor C23's positive lead to resistor R27, both just right of 1J2.
- System 6: clip to the top (positive) lead of C23 and the bottom lead of R27.
- System 7: clip to the bottom (positive) lead of C23 and the bottom lead of R27.
- Take care: one side of R27 is ground, and using the wrong end shorts the supply.
- System 3 and 4 boards do not need the 12 V either once the reset modification has been done.
Systems
Related tips
- A System 7 CPU board can run any System 3 to 7 game
- Which CPU boards can run which system firmware
- Identifying a System 3 to 7 CPU board
- What changed on the System 6A CPU board
- System 6 CPU board test points
- System 7 CPU board test points
- System 6 CPU board jumpers J1 to J6
- Chips a System 7 CPU board needs to run the Williams test ROM
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)