Remove rear cover and look for a large transformer with a red lead that goes to the tube with a rubber cap. On this transformer you will see two controls. One marked "focus" and the other marked "screen". Mark the position of the "screen" control and turn anti-clockwise very slightly and the lines should now be gone.
BE VERY CAREFUL AND DON'T TOUCH ANYTHING ELSE ESPECIALLY THE RUBBER CAP AS THE CONNECTOR UNDER THIS CAP OPERATES AT 2500 VOLTS NOMINAL AND HOLDS A CHARGE EVEN WITH THE SET UNPLUGGED.
sparky, April 2006