I am only a beginner, but have learned alot. Get a can of freeze
spray, get to the chassis, turn on the set, and start spraying
components around the flyback, HOT, and SMPS. You can find a good deal
of faulty components by luck with this stuff. Wish I could help more,
but I have no idea why the set would cycle on and off at a steady
frequency like that. I'm sure the fix is in the question.

I don't think the problem is an overheated component. It only happens when
the TV is turned on cold. Once it warms up, the problem goes away. If the TV
is warm, and powered off, and then powered on, there is no problem.