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Samsung LN-T4065F LCD TV 40" The TV is 10 years old and has 5700 viewing hours. The backlight is flashing on and off at a rate of about 3 times/sec. You can see a video of it here: https://www.dropbox.com/s/q7ngflkituz774

This used to happen periodically then go away overnight. Now it’s not going away. How can I debug if this is an inverter problem? I have a multi-meter. Or should I just buy the $17 inverter and hope for the best?

The backlight inverter is damaged. Needs to be replaced. Requires soldering. You could send the board off to a board repair shop in your area or mail in