Logic-probing the switch matrix

Steps

• Defeat the slam switch on the CPU, power up and let the game boot, then unplug J6 and J7.
• Z8 (7404): pairs 1/2, 3/4, 5/6, 9/8, 11/10 (strobes 0-4) should pulse on both pins. Z8 fails more than the return chips.
• Z9 (7405): pairs 2/1, 4/3, 6/5, 8/9, 10/11, 12/13 (returns 0-5) should be high on both pins.
• Z28 (7405): pairs 4/3 and 10/11 (returns 6-7) should be high.
• In each pair the first pin goes to U5 and the second to the connector.

Systems

• Gottlieb System 1

Related tips

• System 1 switch matrix layout
• Slam and outhole switches sit outside the matrix
• Test PROM switch actions
• Testing switch return buffers Z9 and Z28
• Switch matrix dead after coil or GI voltage touched it
• Switch strobes missing at Z8
• CPU plug A1J7 (playfield switches) pins
• CPU plug A1J6 (coin door) pins

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)