In certain cases, specific kinds of physical contact with the TinyNES enclosure may cause visual interference in the output video signal. Several examples of this interference are shown here.
In this example, the sky should appear as solid light blue, but instead it appears with horizontal bars of pink, orange, or black which crawl vertically, flicker, and/or may have jagged edges.
This issue occurs because 3 normally unused pins on the PPU chip are connected to a header for use with optional RGB output. If the header is not being used, these 3 pins are left floating, which means that they are not driven to a predictable high or a low state.
Despite not being utilized, the high or low state of these pins may still affect the background color palette. Tiny changes to the electromagnetic environment around these signals, such as those caused by the presence of human fingers, may translate into visible changes in the video image.
This issue is completely mitigated by installing the jumper board as described in this guide, which connects these three pins to ground and fully resolves the problem.
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