What each 6821 PIA on the CPU board controls
U10: sound output selects, solenoid drivers and flipper relay K1. U38: switch matrix rows and columns, special solenoids A and D. U41: display data (1J22), special solenoids B and C. U42: sound board (1J21). U51: display circuit on 1J1 to 1J3. U54: lamp matrix rows and columns, special solenoids E and F. All six tie to the reset and IRQ lines, so any one can stop the board booting.
Systems
Related tips
- Testing the 6821 PIAs in circuit with a meter
- Checking ground and +5 V on the CPU board
- Which System 11 CPU boards fit which games
- Running the CPU board on the bench
- Checking the CPU clock signal
- CPU RAM at U25
- CPU board test switches SW1 and SW2
- Checking PIA outputs with the test EPROM running
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)