LED stays on; U9 pins 3, 36 and 37 show no pulsing.

No clock at the CPU: U15, U16, C14/C15

Cause: The clock chips U15 (MC3459L or 74S37, the most common failure) or U16 (9602), or the 470 pF capacitors C14/C15.

Checks

• Logic probe on U9 pins 3, 36 and 37: they should pulse. A meter reads about 2.5 V on each.

Fix

• Replace U15 first, then U16, then C14 and C15.

Systems

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

Related tips

• Fit new C14 and C15 for a cleaner reset and clock
• Tracing the VMA signal through U19, U14 and U15
• U9 pin 5 (VMA) is not pulsing
• After work on U15 or U16, check the traces under them
• Building a replacement SRC pack from discrete parts
• Logic probe states in attract mode: U16 9602 and U15 MC3459
• Making the test LED for the test EPROM
• Flicker but no first flash

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