The MPU completes its seven LED flashes but the game does not run correctly; audits and high scores may all show the same repeated value (for example 74).

M-200 flashes seven times but the game misbehaves or repeats one number in audits

Cause: A slow 5101-3 (300 ns) RAM fitted to an M-200, which runs faster and needs the 100 ns 5101-1.

Checks

• Read the suffix on both 5101 RAM chips (U13 is the second one).

Fix

• Replace any 5101-3 with a 5101-1 on an M-200. The 5101-3 is fine on Bally and M-100 boards.
• In a Bally game, the U13 RAM can simply be removed.

Systems

• Stern MPU-200

Related tips

• Intermittent or dead MPU from old closed-frame sockets
• Seven flashes, then it starts over endlessly
• Stern M-200 occasionally will not boot and the MPU reset button does nothing
• Seven flashes but no attract mode
• Flicker but no first flash
• Test EPROM: the least an MPU needs to run it
• Stern games from 1980 on need an M-200 MPU
• MPU LED never lights at all

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