Lupine Systems -- It's A WOLF Thing! -- Getting Rid of Nintendo Video Inverter

How to Get Rid of Nintendo's Video Inverter

by Spike Tsasmali

One annoyance that has always bugged the amusement industry is Nintendo's use of negative video. Games such as Donkey Kong, Donkey Kong Jr., Popeye and Punch-Out all generate negative video.

So just what is negative video and why is this an annoyance? Good question. Here is the answer...

Negative video means just that. The electronic video signal is backwards from "normal". For example, regular video would produce a white picture when the voltage is high and a black picture when the voltage is low. Negative video produces a black picture when the voltage is high and a white picture when the voltage is low.

What this means is that you cannot replace a Nintendo monitor with a regular Wells-Gardner or Electrohome-style monitor without first inverting the video. On later models of Nintendo games, the monitor included a small "video inverter" module which could easily be removed and wired to work with a new monitor, but older games like Donkey Kong and RadarScope did not have this option. The only way to keep those older Nintendo games alive was to fix the monitor at any cost, or build or salvage a video inverter from a later model monitor and install it onto a new monitor chassis.

Well, there is an easier way when it comes to Donkey Kong and Donkey Kong Jr. games. Simply invert the data from the color PROM's at 2E and 2F of the CPU board. This can be done by reading the PROM data onto your PROM burner, reading the data as 2's Compliment, then burning new 2E and 2F PROMs (82S129's). Or you can build this nifty Video Color Corrector board. This tiny single-sided PC board will re-use your original 2E and 2F PROMs and will digitally invert the video to "normal" without having to wire up an analog video inverter between the game board and the monitor. This will save all the extra wiring needed and will facilitate the use of a Donkey Kong to JAMMA Adaptor.

The layout file dkcolor.pcb includes component placement diagram and parts list on the 1 Mid Layer.

All you need to build this simple project can be purchased at Radio Shack for less than $10, and most folks will find all the parts they need in their junk box.

Once you have built this board, remove the chips from 2E and 2F on the DK/DK Jr. CPU board and install these chips in their respective sockets on the Color Corrector board (refer to the Component Placement Diagram on the 1 Mid Layer of the PC board layout file). Be sure to observe chip notch direction!! Then install this board in the empty sockets once occupied by the 2E and 2F PROMs. Press firmly to seat the board tightly into the sockets! The video coming from this board will now be normal and can be displayed on any regular RGB monitor.

Remember that Lupine Systems offers complete parts kits less PC board for all items mentioned on the website. Just send an E-mail to WOOFY for more information!

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