Grundig TV - a thermic problem

[vioviovio]

I have a Grundig ST70- 574 SAT TV, chassis CUC 5820. When the room temperature is above 25 Celsius, on the screen appears some slime horrizontal white bright lines who flashes -perhaps an optical illussion of 1/2 frame. The intensities and frequences of that 'lines' is related not only with the ambience temperature but also with the values of brightness and contrast. In order to be able to watch a TV program I have to decrease the values of brightness and contrast to a level when the flashing 'lines' dissappear or to open the room windows. In full winter!
Also, before that probleme appeared with my TV set , if I seted a high level of brightness+ white image screen = geometrical deformation of vertical lines.
If you have a suggestion, please reply. I have some experience in TV repairs and theory, but not enough to solve my problem. (still-- i suspect vert sync).

[kilork]

Hi! I think you should check (replace) the electrolyt capicators in
frame stage and Power Supply also (delivering the power to frame)