MPU U9 voltages that show a working reset section

With the MPU on, a working reset section and clock give roughly: U9 pin 3 at 2.4 V, pin 36 at 2.6 V, pin 5 at 2.8 V and pin 40 at 4.75-5.5 V (meter readings of pulsing lines). If these are right, look at U6, U9, U11, their sockets or the ROM jumpers instead.

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
• Resets from a bad MPU J4 power connector
• Testing the MPU reset circuit at U9 pin 40
• Quick test of reset transistor Q1
• Reading the MPU flash code
• DS1811 reset chip: which version to use
• What each MPU LED flash proves
• What a good MPU does straight after the last flash

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