I would adjust the screen volts on the eht transformer somewhere near the focus adjustment. There is 25,000 volts or so around here so unless you are familiar with working on high voltage equipment leave well alone as it is very dangerous.
paddy
March 2007
Sounds like flyback lines (always there but normally not visible), and usually accompanied with an overbright picture.
You'll need an engineer to repair it.
It will probably turn out to be a leaky capacitor - cheap & most likely cause, especially on older sets.
It can be due to failure of more expensive components, including the cathode ray tube (especially, but not always) if there is no picture displayed behind the lines. That would be very expensive but is less common.
Cobweb
March 2007
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