Checking the U4 solenoid spider with a coin tune

Steps

• Turn on DIP switch 23 (tune on coin).
• With the board running, jumper from Z8 pin 4 and briefly touch Z9 pin 1 to fake a coin switch (strobe 1 to return 0).
• Probe Z6 pins 5 (10 chime), 9 (100) and 11 (1000); each should go high during the tune.
• If any stays low, U4 has failed and the board must be replaced.

Systems

• Gottlieb System 1

Related tips

• Which spider chips fail and why
• The six Rockwell "spider" chips on the CPU board
• Swapped U4 or U5 spider still does not work
• Spare chips for System 1 boards
• Check the TC3 jumper plug on the CPU board
• Odd high scores usually mean a bad 5101 RAM
• Aftermarket System 1 CPU boards
• Dead CPU board: first checks

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