Convert a System 3 CPU board to a single 2716 game EPROM at IC14

Steps

• System 3 boards use game ROM sockets IC22 and IC21 for two 512-byte 3624 masked ROMs, plus flipper ROMs at IC20 and IC17; IC14 has solder pads but no socket from the factory.
• Fit a new socket at IC14.
• Find IC15, just down and to the right of the 40-pin PIA nearest the battery holder. A trace runs from between its pins 6 and 7 to a round solder pad.
• Cut that trace on the left side of the round pad.
• Run a short wire-wrap jumper from the round pad to IC15 pin 1. The chip select now enables IC14.
• Burn the game code that was in the two 3624 ROMs into one 2716 EPROM and fit it at IC14.
• The board now works as a System 4 board and runs System 3 or System 4 games; the sockets at IC21 and IC22 are no longer used, so they need not be replaced.

Systems

• Williams System 3

Related tips

• Leon's test EPROM: what to burn and where it goes
• Flipper ROMs at IC17 and IC20: replace the originals with new EPROMs
• Run Firepower on a System 7 CPU board
• System 7: the 2532 goes in IC17, the 2716 in IC20
• System 3/4 sound board jumpers for 7641 PROM vs 2716
• Leon sound board test EPROM
• Identifying a System 3 to 7 CPU board
• A System 7 CPU board can run any System 3 to 7 game

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)