After the test EPROM: refit the game ROM and count flashes

When the PIA outputs all toggle, refit the remaining chips (still with the test EPROM) and repeat the PIA check; any change points to the chip just added. Then put the original U6 back and count the boot flashes: six or seven means a working board.

Systems

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

Related tips

• How the first-flash ROM test works
• ROM and EPROM types used on Bally MPUs
• 9332 masked ROMs can be replaced by 2532 EPROMs as-is
• A 2532 EPROM drops straight into a 9332 ROM position
• Why the MPU has ROM jumpers
• Setting up an MPU for the test EPROM
• Making the test LED for the test EPROM
• U9 signals with the test EPROM running

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