Is the picture affected in any way, (eg. size/interference)?
Has the TV been in storage or anywhere where it may has got slightly damp (eg. near steam in kitchen)?
May be EHT (extremely high voltage) is arcing from flyback transformer or from the cathode ray tube (internally or externally from rim band), or faulty crt base socket. Although, you would normally see some picture interference as it arcs.
Could be due to over-voltage to line output because of incorrect power supply output.
Needs to be checked over to confirm safe use, by an engineer.
Cobweb
July 2005