Hi!

Before suspecting the video chip, check the VRAMs that go with it. Colored
lines (or lines of any sort) are usually what you see when the video RAM
goes bad. Video chips themselves usually fail in more interesting ways.

While I doubt you can solder a new video chip in place, you can certainly
try replacing the VRAMs if you have enough soldering skill (or you get lucky
and they're soldered!).

William