If you own a DTV version 1 then the picture above may look familiar. The problem affects all version 1 units but does not affect version 2, 3, or Hummer units. Essentially it is a moving interference pattern that seems to affect the vertical sides of pixels. It often seems to move or "crawl" around on your screen and certain patterns of pixels can exaggerate the issue. However, this is totally different from the "color flaw" found in Version 2/3/Hummer units. Take a look at the following merged screen capture. This is using the 80-column program. This exxagerates the problem worse because characters are only 4 pixels wide and most vertical lines are only 1 pixel wide. It leaves text looking like a rainbow.
What is it caused by? - From the DTV creator:"The color noise in dtv1 comes from the two xtal harmonics beating against each other. A lowpass filter on the luma may help a bit(much like the LC circuit on the dtv2 & 3). The only way to really stop the beating is to sync the two frequencies off one xtal." Still, if you remove the chroma signal from the video, the resulting black&white image is crystal clear and very still. In fact, it will look better than a real C64. But add the chroma back in and you get the same thing.
Click to enlarge. This screen capture is after removing resistor R14 from the board. This cuts out the chroma circuit. It works almost like an Apple-II series "color killer." Notice how nice and crisp the text is. If you are writing code, working in GEOS, or BASIC, etc.. This is a good solution since it improves clarity dramatically. But for playing games, most of us would prefer the color. Below I've shown two more screenshots of games that are included in the DTV's ROM. These are excellent examples of the issue. You'll need to click the images to see the full-version in order to see the dramatic difference. I would point out that these images were captured in black and white, they were not converted to black and white in a paint program. Believe it or not, the chroma problem is so bad it distorts the luma information.