On a game with a solenoid expander board, the wrong one of a coil pair fires, for example a drop target resets or drops when the outhole kicker should fire.

Drop target falls instead of the ball being kicked out (SEB games)

Cause: The SEB relay is not switching, so the shared driver always reaches the same coil.

Checks

• Run the lamp test (one press of the coin door test button): the SEB relay should click in time with the lamps and its lamp next to the board should flash.
• A buzzing relay rather than a clean click points to the problems in the next entry.

Fix

• Repair the SEB circuit (lamp, SCR, 6 V supply, diodes, relay or opto) as described in the SEB fault list.

Systems

• Bally MPU AS-2518-35

Related tips

• Expander games: check the controlled-lamp power first
• Expander-driven coils fire in pairs: drop target coil fitted without its second diode
• Solenoid expander relay buzzes or does not switch
• Drop target coils misfire after LEDs or a new lamp driver: expander boards need bulbs
• Expander game ejects or drops targets at the wrong time
• Test the coils behind the solenoid expander
• The bulb next to the solenoid expander board must work
• Replacing the hard-to-find 48 V expander relay

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