Testing switch return buffers Z9 and Z28
Steps
- With the board powered and a grounded clip lead:
- Z9 (7405): ground pin 1 and read pin 2; likewise 3/4, 5/6, 9/8, 11/10 and 13/12.
- Z28 (7405): ground pin 3 and read 4, then 11 and read 10.
- Every output should rise to +5 V; if not, replace that chip.
Systems
Related tips
- Test PROM switch actions
- System 1 switch matrix layout
- Logic-probing the switch matrix
- Slam and outhole switches sit outside the matrix
- CPU plug A1J7 (playfield switches) pins
- Switch matrix dead after coil or GI voltage touched it
- CPU plug A1J6 (coin door) pins
- Clamp diode mod to protect U5
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)