Six flashes, then no attract mode, and the LED does not settle to a dim glow.

Six flashes only: 43 V, U10 or U14

Cause: No +43 V reaching the zero-crossing detector (fuse F4 on the rectifier board blown is most likely), U10 PIA or its socket, or U14.

Checks

• Check F4.
• Check for about 21 V DC at MPU TP3.

Fix

• Replace F4 and find why it blew, or replace U10 or U14.

Systems

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

Related tips

• Flicker but no first flash
• Three flashes only: U10 PIA
• MPU stops before the 7th LED flash (no 43 V)
• Logic probe states in attract mode: U9 6800 and U12 555
• Intermittent or dead MPU from old closed-frame sockets
• Logic probe states in attract mode: U16 9602 and U15 MC3459
• Seven flashes but no attract mode
• Garbled player 1 display and strange play from a bad 5101 RAM

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