Switch closures are missed when a System 3 to 6 driver board is used in a System 7 game.

Switches missed in a System 7 game with an older driver board

Cause: Older driver boards have series resistors R204-R211 in the switch matrix (1000 ohm on System 3, 330 ohm on System 4 to 6). System 7 boards replace them with jumpers so a slightly dirty switch is still read.

Checks

• Look at R204-R211 in the upper right of the driver board; System 7 boards have jumpers there.

Fix

• Replace R204-R211 with zero-ohm jumpers, or leave them in and solder wire-wrap jumpers across them. The board then works in System 3 to 7 games.
• If random switch closures appear afterwards in an older game, keep this change in mind as a possible cause, though it is not normally a problem.

Systems

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

Related tips

• Make a System 3-6 driver board work in any game
• Driver board switch matrix resistors R204-R211
• Switch column or row fault on the driver board
• Board or playfield? The switch test jumper method
• Logic-probe the switch matrix
• System 6: game stuck in tilt with switch 1 closed: cracked pins in the 2J2 plug
• Switch matrix connector pins and their chips
• Test the switch PIA IC11 with the Leon test EPROM

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