Firepower 2732 change when IC15 is a 74139 (diode and pull-up variant)

Steps

• Do the same pin 21 cut and A11 jumper as in the plain-jumper method.
• On the solder side, fit a 4.7K 1/4 watt resistor between IC14 pins 20 and 24 as a pull-up for the chip select. Keep it clear of the pin 21 jumper and the cut trace.
• On the component side, fit 1N914 or 1N4148 diodes at J3 and J4 instead of wire jumpers, banded (cathode) end toward the top of the board.
• Use this variant if the plain-jumper method does not work, or if IC15 is a 74139 rather than a 74LS139; the jumper-only method depends on LS logic.

Systems

• Williams System 6 / 6A

Games

• Firepower

Related tips

• Check the battery blocking diode D17
• Firepower: replace the three PROMs with one 2732 at IC14 ("ZIG" method)
• Run Firepower on a System 7 CPU board
• Firepower original ROM layout and jumpers
• Test a playfield switch diode
• Spare diodes for coils and switches
• Bench-testing a -133 MPU: swap the R113 diode for a resistor
• Battery power not reaching the RAM: diode D2

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