The MPU completes seven flashes and then reboots again and again.

Seven flashes, then it starts over endlessly

Cause: A bad U7 6810 RAM, a bad U7 socket or trace, or broken traces or socket contacts at U11, especially around pins 35-40. A broken IRQ line also causes a restart loop.

Checks

• Look for corrosion damage at U7 and U11.

Fix

• Replace U7, the sockets or repair the traces.

Systems

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

Related tips

• One flash only: U7 6810 RAM
• MPU reboots right after the seventh flash
• Seven flashes but no attract mode
• Check the -51/-56 PIA, RAM and amplifier with the test EPROM running
• CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
• Leon test: type 2 sound board RAM IC11
• M-200 flashes seven times but the game misbehaves or repeats one number in audits
• MPU stops before the 7th LED flash (no 43 V)

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