In lamp test the SEB relay buzzes or stays put, and coils on the expander fire wrongly.

Solenoid expander relay buzzes or does not switch

Cause: Cracked .156" header joints, a dead bulb beside the SEB, a failed lamp driver SCR, low 6.5 V from BR1, an open R2 (25 ohm, 5 W) or burned pins on the rectifier board, missing or reversed diodes, pitted relay contacts, or a bad MOC3011 (page 37).

Checks

• Reflow the SEB header pins and replace the bulb next to the board.
• Test the lamp driver SCR that drives the SEB.
• Check the lamp supply voltage, R2 on the rectifier board and its connector pins.
• Each coil on the SEB has two diodes, one across the lugs and one in series with the power wire; check both are present and the right way round, plus the relay's own diode.
• Inspect the relay contacts; file or replace the relay.

Fix

• Replace the failed part; the MOC3011 can be replaced with an NTE3047.

Systems

• Bally MPU AS-2518-35

Related tips

• The bulb next to the solenoid expander board must work
• How the solenoid expander board doubles up coils
• No coils work at all
• Drop target falls instead of the ball being kicked out (SEB games)
• Drop target coils misfire after LEDs or a new lamp driver: expander boards need bulbs
• No playfield coils work
• Replacing the hard-to-find 48 V expander relay
• Expander-driven coils fire in pairs: drop target coil fitted without its second diode

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