Firepower: replace the three PROMs with one 2732 at IC14 ("ZIG" method)

Steps

• Start only with a System 6 or 6A CPU board known to work.
• Check that IC15 is a 74LS139. If it is a plain 74139, use the diode and pull-up variant instead.
• Remove the game ROMs from IC14, IC21, IC22 and IC26.
• On the solder side, notch the wide +5 V trace on both sides of IC14 pin 21 so pin 21 keeps its pad but no longer connects to pin 24. Confirm with a meter that pins 21 and 24 are isolated.
• On the solder side, solder a thin jumper between IC14 pin 21 and pin 34 of the interboard connector, the seventh pin counted from the right. The rightmost pad holds two pins, so count carefully. This feeds address line A11 to IC14.
• On the component side, fit wire jumpers (or zero-ohm resistors) at both J3 and J4 above IC22.
• Burn the combined Firepower code into a 2732 and fit it at IC14, with green 2716 flipper ROMs at IC17 and IC20.
• A board changed this way runs only Firepower until the changes are undone, though Leon's test EPROM still works in it.

Systems

• Williams System 6 / 6A

Games

• Firepower

Related tips

• Firepower 2732 change when IC15 is a 74139 (diode and pull-up variant)
• Run Firepower on a System 7 CPU board
• Use a 2732 instead of a 2532 at U17 on a System 7 CPU board
• Firepower CPU ROM configuration and jumpers
• Lights up but dead after storage: leaked batteries on the board
• Number-of-players backglass lamps dead after playfield work: reseat the MPU plugs
• Game keeps resetting: replace the 5101 RAM (an NVRAM works)
• What changed on the System 6A CPU board

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