Using an LED to see a bench CPU boot

Steps

• Wire an LED in series with a 330 ohm 1/4 W resistor.
• Connect the LED anode (round side) to Z16 pin 15 (top right chip) and the resistor end to Z16 pin 8 (ground).
• Defeat the slam switch, power up and wait: the LED should light after about 5 seconds, as the displays would.
• If it does, go on to the buffer and spider tests; if not, check reset, clock and bus.

Systems

• Gottlieb System 1

Related tips

• CPU board clock check
• CPU address and data line check
• Dead CPU board: first checks
• Aftermarket System 1 CPU boards
• Bench test of coil buffers Z6 and Z7
• Check the TC3 jumper plug on the CPU board
• The six Rockwell "spider" chips on the CPU board
• Testing CPU input buffers Z29 and Z27

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