My grandmother has the TV mentioned in the subject. I don't know exactly what model it is, but the chassis is silver and it has speaker grilles that span both sides all the way up and down. It seems to have developed a horizontal zigzag line that runs all the way up and down the TV, and narrows slightly in the middle. It also flickers red a bit.

Is this a common problem? Has anyone fixed it?

Can you post a picture of what it does,and model number?