The flipper buttons do not move through letters at high score entry; lane change may not work either.

Cannot enter high score initials with the flipper buttons

Cause: On Monday Night Football and earlier, a second, low-voltage normally open switch on the EOS stack feeds the switch matrix and drifts out of adjustment (stuck open or closed). From Robocop on, this switch sits on the cabinet flipper button instead.

Checks

• Run the switch test and operate each flipper.
• On early games, check the matrix switch (the one with the diode) on the flipper EOS stack; on Robocop and later, check the matrix switch on the cabinet button.

Fix

• Adjust or clean the matrix switch so it closes only when the flipper is used.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Service menu scrolls through items on its own: short on a service switch

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)