Lightning Strike?

Assuming this line is across the screen horizontally (side to side), this means the vertical deflection circuitry is dead. In late model sets, there is a Integrated circuit package which drives the vertical yoke coils. Possible defects: the I.C. itself, bad solder connections where it solders to the board, missing voltage source to this I.C. (often around +24 volts), or a bad electrolytic capacitor in the associated circuitry. This latter often results in a non-linear picture, or less than full deflection condition, rather than a thin line only.

It is possible lightning caused this problem, (I've seen some rather illogical damage from lightning ) perhaps it produced enough of a surge to pop the I.C. or a fusible resistor in that voltage source noted above.