The MPU suddenly stops and the game restarts while playing.

Game reboots at random: R11 heating Q5

Cause: Hot resistor R11 (82 ohm 2 W) touching reset transistor Q5 (2N4403) just below it.

Checks

• Look for R11 lying against Q5.

Fix

• Leave an air gap between R11 and Q5, and space R11 off the board.
• Replace Q5.

Systems

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

Related tips

• Replacing the MPU reset section with a DS1811
• MPU LED locked on with no flicker: likely causes
• Testing the MPU reset circuit at U9 pin 40
• Single reset parts that hold the LED on
• Replace a discoloured or carbon R11 on the MPU
• Globetrotters reboots during play (GI stays on)
• Game reboots during play from slam switch noise
• STNG: under-playfield diverter coils lock on during play

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