The regulated 5 V at TP1 sits around 1.6 V.

Only about 1.6 V at solenoid driver TP1

Cause: The LM323 5 V regulator's metal case has a poor path to ground.

Checks

• Check the regulator's mounting screws and the ground under its case.

Fix

• Clean and tighten the mounting so the case grounds firmly.

Systems

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

Related tips

• Solenoid driver TP1 below 5 V with TP5 normal
• Solenoid driver TP5 under 13 V
• MPU locks with LED on because of C23 or Q20 on the solenoid driver board
• Replace filter cap C23 on every game
• Testing C23 for AC ripple
• Replacing filter cap C23
• Route of the +12 V supply to the MPU and 5 V regulator
• Logic 5 V reads over 5.25 V on Bally/Stern: the R49 boost resistor

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