Dead System 6 or 7 CPU board with good reset.

System 6/7 CPU: no clock at the 6802/6808

Cause: The clock oscillator is inside the 6802/6808; only crystal CR1 and capacitors C25 and C26 (27 pF) are external.

Checks

• With a logic probe, look for clock at IC1 pins 38 and 39.

Fix

• Replace crystal CR1 and check C25 and C26.
• If there is still no clock, replace the 6802/6808 at IC1.

Systems

• Williams System 6 / 6A
• Williams System 7

Related tips

• Replacing the 6802 CPU with a 6808
• CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
• CPU locked: check the R/W and VMA lines
• Is it the CPU board or the driver board? Boot the CPU alone
• 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

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