Use a fast enough 5101 RAM

A slow 5101 can pass the boot test yet scramble the score displays because it cannot keep up with display reads. Speeds: PCD5101P 150 ns; 5101-1, -2 and L-1, L-2 450 ns; plain 5101, 5101L, -3 and L-3 650 ns; 5101-8 800 ns. Bally -17/-35 boards need 650 ns or faster and Stern MPU-200 boards 450 ns or faster; the 150 ns PCD5101P suits every board.

Systems

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

Related tips

• Seven flashes but no attract mode
• Two flashes only: U8 5101 RAM
• 5101 RAM speed grades and which MPUs need what
• Keep spare 6800, 6821 and 5101 chips
• One flash only: U7 6810 RAM
• Garbled player 1 display and strange play from a bad 5101 RAM
• MPU board test point voltages
• MPU stops before the 7th LED flash (no 43 V)

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