Way back in the '80s I bought the cheapest 19" TV I could find, from the cheapest retailer in the area (Gemco, maybe (RIP)).
I got it home, plugged it in, and OH NO! There's a big blue splotch along the bottom of the screen! I didn't really want to lug it back to the store, so I phoned the warranty number.
They sent out a guy with a big-ass electromagnetic coil. He did a few passes over the screen. Problem solved.