Very Weird Sony SXRD Symptom...Any Help Would be Greatly Appreciated

[IntelliVolume]

Just yesterday, our trusty Sony KDS-50A2020 rear projection set exhibited a weird symptom that I can't explain. Before I begin scraping together the money we need to upgrade to a 4K set at an even more furious pace, I'd like to know if anyone can lend any insight about this...

The TV's cable box input (a component connection being made from our HD box, so the 1080i signal is upconverted to 1080p by the Sony) suddenly turned a red and green horizontal line distortion on the screen...now, we still get audio, but the picture is a distorted mess of thin red and greenish lines. I thought this may have been our cable box going bad, or perhaps the component cables, but here's the kicker: The distortion remains even when I turn the cable box off (albeit the lines get "weaker").

I tested the "Video 6" HDMI input of the TV, which connects to our Onkyo AVR (receiving signals from an Oppo Blu-ray player), and there is no distortion or issue. It's ONLY on the cable box input.

Can anyone help me diagnose this? Are these symptoms of the dreaded optical block failure? If so, why would it appear only on ONE input? Wouldn't it affect the whole TV?

Should I try a new cable box?

Thank you in advance to anyone that could lend any opinion.