Without the model type/number and the schematics we can't give you a heplful instruction.
The screen shot looks like a failure in the luminance amplifier circuits behind the separation of the color signal. Usually such failures are easy to fix. In some cases the true failure is in the A.G.C. circuit. See
http://audiokarma.org/forums/attachm...chmentid=28089
It looks like a failure in the luminance unit, but it was the A.G.C.!
You can test it by detuning the received TV channel. If there is snow on the screen when I receive no video signal, the luminance amplifier might be OK.