Replacing U2 and U3 with one 2764 EPROM

Steps

• On a System 80 board, remove U2 and U3 and fit a 24-pin socket at U3 (U2 can stay empty). 80A boards are already socketed.
• Program a 2764 with the combined U2+U3 image.
• Bend EPROM pins 20, 22 and 23 out so they touch nothing.
• With wire-wrap wire, link EPROM pin 1 to pins 26, 27 and 28 (this takes +5 V from socket pin 24 to EPROM pin 28).
• Link EPROM pin 2 to pin 21 of a spare 24-pin socket, soldering at the top of that socket pin (A12 to CPU S2).
• Seat the EPROM in that socket offset so EPROM pin 3 is in socket pin 1, with EPROM pins 1, 2, 27, 28 and the bent pins hanging over the edge.
• Link the bent EPROM pin 23 to socket pin 18 near the plastic (A11).
• Plug the assembly into one more socket to protect the board socket, then into U3.
• Link the bent pins 20 and 22 together and carry the wire on to pin 5 of Z10, on the board's top (component) side, which inverts output enable.

Systems

• Gottlieb System 80
• Gottlieb System 80A

Related tips

• Which System 80 test EPROM image to use
• Bench setup for the System 80 test EPROM
• Testing the DIP switch inputs with the test EPROM
• Fitting the 2532 test EPROM at U3 on a board without a piggyback
• System 80 test EPROM LED flash codes
• Test EPROM stalls at the switch matrix RIOT (U4)
• Test EPROM 2: game PROM socket test fails
• Test EPROM: no long flash, or LED stuck on

Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)