Sounds like an intermiddent connection, May be a plug in connector came loose.
If you are comfortable with TV repair, and understand chassis can be hot(live), and the high voltage line to tube, then I would remove back, stay insulated and with insulated tool,
Poke around, jiggle and try to determine bad connection, Could even be a cracked board,
Or solder connection, Magnifier will help. A mirror so you can see picture will be helpful, or a second set of eyes. Stay insulated and Safe, Good Luck
Intermittent parts are less common.
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