Samsung tv MODEL UN40F6300AFXZA

This model set had defective LED lamps from the factory and only lasted 1000 plus hrs...You can get lamps that will last from shopjimmy that will fix the issue for about $60 with shipping. Its not a hard job changing them, just takes some patience and care when handling the screen as it's extremely fragile on most lower price sets.

The next thing to try is the LED screen itself could be costly it could be cheaper to call out an engineer to diagnose the fault then it's up to you whether to let him fix it or if your confident buy part or parts on Amazon and replace yourself I hope this helps

perhaps the backlight invertor driver circuit.

Samsung TV Repair Part Number Identification Backlight Inverters LED...
See where the wires from the long LED strips on the both sides of the screen lead you to.

does your model have separate board for backlight ? or is it integrated with TCON ?

It rather seems to depend on the model. I have seen Two videos on YouTube, one says it could be the LED back lighter, with a burned or shorted out LED(s). In the other it says it is the power supply board. But both were different Samsung TV's. The LED one if that looks tricky to do. If it is the power board, which I think it could be, you should be able to get the full board fairly cheap. Just be careful with the voltages when removing it, if you intend to do it yourself.
To see the Videos just type "Samsung TV blinking lights" into YouTube.

The blinking is a trouble code. Your TV is in need of repair.

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience.

How many times do this standby light blinks at a time of switch on? These blinks are fault indications. From the number of these blinks, you can get an idea about the faulty circuit section inside it. Count it. If you wish to get more details about the blinking codes to Sony TVs, check this link.

My TV is (same model is doing the same thing). The manual shows that the 3 blinking lights indicate "LED may be defective. Please contact a certified technician."

Note: When I power my TV off (unplug) and back on, the TV's left indicator light is solid for less than a second ("Stadby state") then the right light blinks ("The picture will automatically appear in about 15 seconds") for about 15 seconds. This pattern is repeated numerous times (I think it was 5 times). I believe the TV must be failing some power-on test. Aftere failing 5 times it gives LED may be defective indication.

Try to remove the vertical IC sometimes it become Shorted causing the B+ to drop. after removing try to switch on back check the B+ if ok and the LED not blinking then change the vertical IC.

On older Sony, sometimes a power surge causes the set to be in shut down mode. Try unplugging for 5 minutes and then plug in and try. This many times will fix.