The company which [Eric Wright] works for recently bought a Nintendo VS. It had Ice Climber installed as one of the titles but they asked the vendor if it was possible to swap it out for the Duck Hunt ROM. They had the ROM but not a light gun that would work with the system. [Eric] suggested they buy it with Duck Hunt and hack an NES Zapper to work with the VS cabinet.
Let’s take a step back for a moment. The Nintendo VS was a coin-operated gaming cabinet you would find in an Arcade. Luckily there’s quite a bit of information about the original hardware on the web. Some research helped him discover that electronically the only difference between the arcade and home versions of the Zapper is that the sensor capture is inverted. This was fixed by replacing a transistor in the gun with a jumper wire. The next challenge was figuring out how to wire the gun up to the second controller port. And finally he patched the ROM to work with the incorrect PPU as the right chip was not easily sourced.