Chips a System 7 CPU board needs to run the Williams test ROM

With the Williams test ROM the CPU runs without IC13, IC14, IC16, IC19, IC20 and IC26, but needs IC7, IC10, IC11, IC12, IC15, IC18 and IC31. The numeric LED blinks then counts 0 to 9 if the CPU runs, then blinks to show a missing IC; refitting chips one at a time changes the number. A flashing 8 means the CPU is nearly running and is looking for the driver board.

Systems

• Williams System 7

Related tips

• 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
• System 7 CPU ROM sockets
• Obsolete chips on System 3 to 7 CPU boards
• CPU chips Leon's test code does not need
• CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
• Identifying a System 3 to 7 CPU board

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