Random lockups, locked-on coils, burnt driver transistors, a blown solenoid PIA, or a game that will not start.

Lockups and locked-on coils from worn chip sockets

Cause: Original closed-frame sockets (often Scanbe brand) grip only the thin side of the chip legs and lose contact with age; even open-frame "RN" sockets wear out.

Checks

• Identify closed-frame sockets (no board visible under them).
• When removing, look for broken pins inside.

Fix

• Replace all closed-frame sockets on the CPU board (the 40-pin CPU socket and the 24-pin ROM/RAM sockets) and any on the driver board.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Remove an old chip socket
• CPU locked: check the EPROM chip select
• Solenoid fuse F2 blows at power-up as every coil fires: CPU blanking circuit
• Replacement CPU board: game won't start though tests pass: DIP switches reversed
• Game always powers up in audit mode: bad 5101 memory chip
• Chips that commonly fail on System 3-7 boards
• Which RAM chips go at IC13 and IC16
• System 7 CPU ROM sockets

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