The MPU LED does not complete its seventh flash at power-on.

MPU stops before the seventh flash: check the 43 V at R113

Cause: Without the 43 V zero-cross input the boot does not finish: blown 43 V fuse, an open R113, or battery corrosion around it.

Checks

• Measure 43 V DC on the left side of R113, just below and right of MPU connector J4.
• If the left side has 43 V and the right side reads nothing, R113 is open (page 18).
• If both sides show 43 V, look for battery corrosion damage in that area of the board.

Fix

• Replace R113 (2K, 1/4 W) or repair the corrosion damage.

This check is done with the game on; keep fingers off the line-voltage wiring and the high-voltage display circuit.

Systems

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

Related tips

• MPU LED locked on with no flicker: likely causes
• What each MPU LED flash proves
• No seventh MPU flash with a good solenoid fuse
• Good MPU stays LED-on with a PC power supply
• MPU reboots right after the seventh flash
• MPU stops before the 7th LED flash (no 43 V)
• Reading the MPU flash code
• MPU boots only when U9 pins 39 and 40 are shorted

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