All seven flashes, then the game hangs.

Game locks up after the seventh flash

Cause: A failed isolation diode CR3 on the sound board dragging the 43 V down; also a weak C23 on the solenoid driver board, or U12 (555) or C17 on the MPU.

Checks

• Unplug the sound board and reboot; if the game now runs, test CR3 on the sound board.

Fix

• Replace CR3 on the sound board, C23 on the SDB, or U12/C17 on the MPU as found.

Systems

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

Related tips

• Spare sound board works on the bench but is silent in the game: no -5 V, bad 7905
• MPU stops before the 7th flash until sound board power is unplugged: replace CR3
• Sound module -32 and -50 test points
• Sound Plus -56 and vocalizer test points
• Squawk & Talk -61 and Say It Again -81 test points
• Odd 43 V coil faults on games with the early AS-2518-32 sound board
• No sound at all: start with the amplifier hiss
• Sound board chip 86L93 can be replaced by a 74LS93

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