Insufficient vertical height

Question

I have a Panasonic TV Model No CT-32G13W. When the set is powered on, the picture fills the entire screen. At some point in time, retrace lines appear at the bottom of the screen and move vertically upwards resulting into a narrow picture. i know that it is a strong possibility that the problem is probably in the vertical output circuit. I tried to get a schematic from a vendor on the internet but the print is very poor and is impossible to read. I would very much appreciate if you would assist me in solving this problem.