I was using my original SNES from near the release of the system about a year ago and noticed the same issue with screen tearing in games like yoshi's island and other super fx games.
I assumed it was the ppu dying in the SNES because of age, not the TV causing the issue. I've since switched to a revision 2 board SNES on the same TV and setup (scart to component) and have no problems at all.
I would be wary of a dying ppu in that SNES as screen tearing can be a symptom of a chip on its last legs. The system is basically a loss at that point. Unfortunately they don't last forever.