Replace a discoloured or carbon R11 on the MPU

R11 (82 ohm) runs hot. After a rectifier upgrade the 11.9 V line can sit near 14 V, which pushes an old carbon resistor out of spec until it drifts or opens, and an open R11 causes resets. Fit a new 2 W part if the old one is discoloured or carbon type, and stand it off the board.

Systems

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

Related tips

• Game reboots at random: R11 heating Q5
• Replacing the MPU reset section with a DS1811
• Testing an MPU in the game with only J4 connected
• MPU board test points
• MPU board test point voltages
• Telling a -133 MPU from a -35 or -17
• Converting a -133 MPU to a -35
• Setting up an MPU for the test EPROM

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