Pressing the flipper buttons does not move the lit lanes.

Pre-Fliptronics: flipper lane change does not work

Cause: Almost always the 4N25 opto-isolators on the driver board, U7 for the left flipper and U8 for the right. Later Fliptronics boards no longer have them or the flipper relay.

Checks

• Check which side fails.

Fix

• Replace U7 or U8 (4N25).

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix

Related tips

• Flipper buttons not seen by the game (pre-Fliptronics)
• Funhouse: flipper buttons won't step through high score initials
• Row or column "ground short" errors
• Lane change not working on Taxi and later System 11 games
• Pre-Fliptronics: a flipper does nothing
• Upper right flipper only buzzes while the magnet holds the ball: failed opto-isolator
• Pre-Fliptronics: weak flipper
• Pre-Fliptronics games need a driver board with the flipper relay

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)