CPU board will not run; one or more address lines are dead beyond the CPU.

Address buffer check: 8T97s at IC3, IC4 and IC8

Cause: A failed 8T97 address buffer at IC3, IC4 or IC8.

Checks

• With a logic probe compare each buffer input with its output; they should match.
• IC4: A0 in pin 2 out 3, A1 in 4 out 5, A2 in 6 out 7, A3 in 10 out 9, A4 in 12 out 11, A5 in 14 out 13.
• IC3: A6 in 2 out 3, A7 in 4 out 5, A8 in 6 out 7, A9 in 10 out 9, A10 in 12 out 11, A11 in 14 out 13.
• IC8: VMA in 14 out 13, A12 in 12 out 11, A13 in 10 out 9, A14 in 6 out 7, A15 in 4 out 5, R/W in 2 out 3.
• If an address line is missing at a ROM, RAM or PIA, check continuity from the buffer output pin.

Fix

• Replace the bad 8T97 with a 74LS367 or 74LS365.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• 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
• Why the CPU LEDs stay on when the program does not run
• Run the System 3-6 built-in CPU test (SW1)
• CPU locked: check the R/W and VMA lines
• Is it the CPU board or the driver board? Boot the CPU alone
• System 3/4 CPU: no clock at the 6800 or MC6875

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