Mod2: one 2732 at U2 on a -17 or M-100 (combines U2 and U6 code)

Steps

• Combine the U2 and U6 images into one file with a binary copy, U2 first then U6 (for example a DOS COPY /B of the U2 file plus the U6 file into one .732 file), and burn it to a 2732 (2732A parts worked best for the author).
• Keep E6-E7 and E8-E10; remove E1-E2 and E3-E4.
• Solder side: cut the trace to U18 pin 4 and wire the via above U3 pin 6 to U18 pin 5.
• Component side: at the top right of U2 (near pin 13) find the via with a trace running straight down; cut that trace off the via.
• Component side: wire that via to pad E4, which links E4 to U2 pin 21.
• Component side: scrape the solder mask off the wide ground trace to the right of U2 and wire it to pad E3 (grounds U2 pin 20).

Systems

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

Related tips

• Mod4: convert a -17 or M-100 to take 2732s at U2 and U6 (runs any Bally game)
• -17 and M-100 boards cannot run 1979-1985 games without modification
• Bally -17 and Stern M-100 ROM jumper settings
• A Stern M-200 set for 2732s runs any Bally or Stern game 1977-1985
• MPU board test point voltages
• Testing an MPU in the game with only J4 connected
• Using a PC power supply as an MPU bench supply: which wires
• Turning on an ATX PC supply without a motherboard

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