Checking PIA outputs with the test EPROM running

Steps

• With the test EPROM running, pins 2 to 17 of all seven PIAs (U9, U10, U38, U41, U42, U51, U54) should switch between 0 and 5 V once a second.
• Exceptions: U38 pins 2-9 only toggle when 1J10 pins 1-9 are grounded; U9 pins 10-17 do not toggle (they feed DAC U2); U51 pin 9 is tied to ground through jumper W7.
• If an output is stuck, short it to the next output. If both then move, the PIA is bad. If neither moves, it is either the PIA or a short on that line.
• To tell which, cut the output trace or lift the pin (repair it after): if the pin now moves there is a short downstream, if not the PIA is bad.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Leon test EPROM does not run: check the 6808 and its pins
• Running the CPU board on the bench
• What each 6821 PIA on the CPU board controls
• Testing the 6821 PIAs in circuit with a meter
• Using the Williams System 11 test fixture EPROM
• Find out how the board died: failures cascade to the PIAs
• Other quick PIA checks: swap or touch test
• Setting up Leon's System 11 CPU test EPROM

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)