Logic-probe the switch matrix

Steps

• Unplug 2J2. With the game on (switch test or attract), every 2J2 pin should pulse. A pin stuck high or low points to its 7406 or the PIA.
• Unplug 2J2 and 2J3 and probe the 2J3 pins: there should be no activity. Pulsing means a shorted row.
• Plug both back in, probe 2J3 pin 9 (row 1) and close a row 1 switch such as the plumb bob tilt: the pin pulses while the switch is closed.
• On 2J2 pin 9 (column 1) the probe tone changes as the plumb bob closes.
• Some games do not use rows 7 or 8.

Systems

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

Related tips

• Switch matrix connector pins and their chips
• Driver board switch matrix resistors R204-R211
• Switch matrix column test at 2J2 with Leon's code
• Switch matrix row test at 2J3 with Leon's code
• Whole game dead after working on a flipper EOS switch
• Board or playfield? The switch test jumper method
• Leon test: switch column drives (2J2)
• Leon test: switch row inputs (2J3)

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