Clear stuck switches using switch test

Steps

• Remove all balls so the trough switches open. Tape between contacts of any switch that closes when the playfield is raised (spinners often do).
• Enter switch test (five presses on sound-board games, four on chime games).
• The display shows the last stuck switch; find it with the manual and fix it, then the next stuck one appears (page 41).
• Carry on until no switch number is shown.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Switches register with the wrong numbers
• Test a playfield switch diode
• What bad switch diodes do to the matrix
• MPU switch connector pins J2 and J3
• Random game faults when a switch without a diode sticks
• Keep opto switches clear
• Some games add a sixth switch strobe ST5 (switches 41-48)
• Small capacitors across switches lengthen closures

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)