Dead System 3 or 4 CPU board with good reset.

System 3/4 CPU: no clock at the 6800 or MC6875

Cause: Failed crystal or MC6875 clock chip at IC5.

Checks

• With a logic probe, look for clock at IC1 pins 3, 36 and 37.
• Check the MC6875 (IC5, left of the crystal) at pins 7, 13 and 15; pin 15 feeds IC1 pin 3 and pin 13 feeds IC1 pins 36 and 37.

Fix

• Replace the crystal first (3.58 MHz; a 3.579545 MHz part works), since the MC6875 is obsolete.
• Only then look for a replacement MC6875.

Systems

• Williams System 3
• Williams System 4

Related tips

• CPU locked: check the R/W and VMA lines
• CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
• Is it the CPU board or the driver board? Boot the CPU alone
• Identifying a System 3 to 7 CPU board
• A System 7 CPU board can run any System 3 to 7 game
• Good reset and clock but LEDs locked: check IC17 and its bus lines
• CPU locked: check the EPROM chip select
• System 3 CPU board ROM layout

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