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Hello, Sorry you're having issues Paul. This is a frustrating problem. but fortunately not the worst we've seen and something we've repaired before many times. It's caused by a failing "Mainboard" in the TV. It's the only part in the set that can cause the set to cycle off and on on it's own before powering up and staying on.
This isn't caused by any loose cabling/connections inside of the set, it's caused by a faulty EEPROM (processor) on the mainboard and the solution is to replace the Mainboard, or the EEPROM (the mainboard is "plug and play" however the EEPROM is a multi-pin IC that requires excellent soldering skills to replace).
This model number is "fairly" recent however, so can you tell me roughly how long you've owned the set for please (under one year or over)?
If the set is over one year from the date of purchase, then the Mainboard, is commonly available at the link below for your TV, but is currently showing as out of stock:
In fact, that board is showing as "out of stock" through every vendor out there. The only solution to have this fixed, is to contact a shop and have them replace the EEPROM on the Mainboard - which is on average a $175 repair on ts set and a shop can be located at the link below:
Other than that, I'm sorry for the bad news here and wish there were a quick fix.
Let me know if you need further help. Also, please do click a 3-5 STAR rating for my efforts before you go. That is how I am credited for my efforts by the site.