Test the switch PIA IC11 with the Leon test EPROM

Steps

• Remove F2 and F3 and unplug 2J2 and 2J3.
• Fit the Leon test EPROM in CPU socket IC17 and switch on.
• To test IC11 pins 2-9, ground every pin of 2J3 or they will not toggle.
• With the tester LED's plain lead on +5 V (TP9 on System 6/7, or interboard pin 1), touch IC11 pins 2-17, 19 and 39: each should switch high and low every second. Data pins 26-33 should pulse (use a logic probe). Reset pin 34 should be high.
• Any of pins 2-17 not toggling means a bad PIA: remove it, fit a socket and a new 6821.

Systems

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

Related tips

• Test the driver board PIAs IC5, IC10 and IC11 with Leon's code
• Test the CPU board PIA IC18 with Leon's code
• Leon code running but LEDs dark: bad CPU PIA IC18
• Leon's test EPROM fitted but the LEDs do not start flashing
• CPU locks up as soon as the driver board is connected
• Damage after the black and white plugs were swapped
• Displays show only every other digit ("0_0_0")
• One PIA output does not toggle under the test EPROM

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