System 3 CPU board ROM layout

System 3 boards hold the game code in two 512-byte PROMs at IC21 and IC22 and the two flipper ROMs (2716 EPROM or 2316 mask ROM) at IC17 and IC20. IC14 has pads but no socket and there are no pads at all for IC26. The battery holder is at the middle left, and game settings are made on CPU board DIP switches.

Systems

• Williams System 3

Related tips

• Which System 3 to 7 games use which flipper ROM system
• A System 7 CPU board can run any System 3 to 7 game
• 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
• Flipper ROM color codes by system
• CPU DIP switches: used by System 3, ignored from System 4 on
• Power a System 3 to 7 CPU board on the bench with a PC power supply

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