Fitting the combined 2764 to a System 3/4 CPU board

Steps

• Bend 2764 pins 2, 22 and 23 outward so they stay clear of the socket.
• Plug it into any one of the IC20, IC17 or IC14 sockets, offset so 2764 pin 14 sits in socket pin 12 (the 28-pin chip overhangs the 24-pin socket). On a Firepower board already converted to a combo ROM in IC14, use IC17 instead, as IC14 is rewired.
• Solder pins 1, 26, 27 and 28 of the 2764 together with a wire across their tops.
• Remove IC15 from the board.
• Wire 2764 pin 2 to IC15 hole 13, pin 22 to hole 12, and pin 23 to hole 14.
• Putting a socket and a small plug at IC15 makes it easy to return the board to standard chips.

Systems

• Williams System 3
• Williams System 4

Related tips

• Identifying a System 3 to 7 CPU board
• A System 7 CPU board can run any System 3 to 7 game
• System 3 CPU board ROM layout
• Which CPU boards can run which system firmware
• Obsolete chips on System 3 to 7 CPU boards
• How a good System 3 to 7 CPU behaves at power-on
• System 4 CPU board changes and ROM layout
• CPU DIP switches: used by System 3, ignored from System 4 on

Source: Use any Williams 3/4 or type 6 board for any pinball from this series (2764 EPROM remapping)