Check the wire from a coil back to the solenoid driver board

Steps

• Switch the game off.
• Clip one meter lead to the coil lug that the unbanded end of the diode is on.
• Look up the SDB connector and pin for that coil in the manual and touch the other lead there.
• Expect about 0 ohms. Around 30 ohms means you are on the wrong pin (reading through another coil).

Systems

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

Related tips

• Solenoid driver board J3 pin functions
• One coil dead with a good transistor and power at the coil
• Test solenoid driver transistors with the game off
• Test the coils behind the solenoid expander
• AS-2518-16 and AS-2518-22 solenoid driver boards interchange
• No coils work at all
• The solenoid driver board also carries the 190 V display supply
• Solenoid driver board: transistor, diode, resistor and connector for each driver

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