Adding a ground jumper at C23

Steps

• On 1979 and later driver boards, on the solder side, jumper the negative lead of C23 to the wide ground trace just below it.
• On earlier boards, jumper the C23 negative lead to J3 pins 18-22 instead (they are all tied together).
• This stops the 5 V regulator ground looping out to the power supply and back, which burns driver J3 pin 10.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• Ground mod for the solenoid return at J3 pins 23-24
• Jumper TP1 to TP3 on the solenoid driver
• Solenoid driver/regulator board test point voltages
• Skip the driver board mods on Baby Pac-Man
• Solenoid driver/voltage regulator board test points
• Solenoid driver board: how the MPU selects a coil
• Solenoid driver board: test points and regulators on the layout aid
• Testing C23 for AC ripple

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