Switches do not register (bench or game).

Switch strobes missing at Z8

Cause: Z8 (7404) strobe buffer, or the U5 spider behind it.

Checks

• Logic probe Z8: pins 1/2 strobe 0, 3/4 strobe 1, 5/6 strobe 2, 9/8 strobe 3, 11/10 strobe 4; both pins of each pair should pulse (13/12 is unused).

Fix

• Pulsing on the input pin only: replace Z8.
• No pulsing on the input pin: U5 has failed and the board must be replaced.

Systems

• Gottlieb System 1

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)