System 6 CPU board test points

TP1 +12 V unregulated; TP2 NMI, +5 V, 0 V while SW1 is pressed; TP3 memory protect, +5 V with the coin door interlock closed, 0 V open; TP4 blanking, +5 V running, 0 V for about 1 second at power-on; TP5 IRQ; TP6 phase 2 clock; TP7 CMOS RAM supply, 4.3 V on and 3.9 V off (low means weak batteries); TP8 reset, 0 V for the first second then +5 V; TP9 +5 V; TP10 ground. System 3 and 4 boards have no test points.

Systems

• Williams System 6 / 6A

Related tips

• Identifying a System 3 to 7 CPU board
• What changed on the System 6A CPU board
• System 6 CPU board jumpers J1 to J6
• A System 7 CPU board can run any System 3 to 7 game
• Run a System 6/7 CPU board on +5 V only
• Which CPU boards can run which system firmware
• Obsolete chips on System 3 to 7 CPU boards
• How a good System 3 to 7 CPU behaves at power-on

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)