That it's a 480p or 480i issue. With that you can try out various ideas as you presented but here's what I'm seeing. TV techs no longer try to get old gear working with hacks or converters. My bet is that the lore is getting lost or there's no money in it.
I have a 50" Samsung DLP TV circa 2006 that has flickering dark and light lines across the screen. These lines change in intensity, thickness, and angles. Sometimes they scroll, sometimes they wiggle. See here http://www.imagebam.com/image/96a28d443081936. I can't seem to find this exact problem described here.
When I select menu, the menu items do not have the flickering lines the so that should eliminate the wheel or some other mechanical problem. similar posts had solutions such as eliminating a ground loop, but this model has no ground. I also untangled power cords from the coaxial. No change.
I have donated the TV to the cabin I am leasing for the winter and they are use an SD digital converter using coaxial from the cable/satilite company. (Can't tell what company, it's not on any of the hardware) My suspicion is the converter emits 480p and my TV's coaxial input only accepts 480i, or vice versa. I believe this because I had this same problem with the same flickering lines with this TV at my house when using the HDMI (DVI) port and had to get Comcast to reprogram my box to emit 1080p instead of 1080i, or vice versa, I can't remember. Nowhere does Samsung say what kind of inputs the coaxial accepts.
I am not sure what to do at this point but I am wondering if it would be as simple as using some kind of converter to convert it to compsite, component, or HDMI, which do accept both "i" and "p". I am not sure if that even exists. Perhaps I can run the signal through a DVD player?