How do I fix an LED TV with no picture or sound?

SOURCE: Samsung TV won't turn on- trying to fix it. A challenging problem

I had the same problem. I live in NJ and called the local authorized "service provide" listed on the Samsung website. What a joke. Quoted $350 just to show up, never showed up. So I opened my own TV. Took off the plastic back (10 screws) took off the large metal RF shield (12-14 screws) and noticed a blown component. The markings on the component were KL15L and it is apparently an NTC Thermistor. Obviously it got fried and not knowing if there was other damage I decided to set out to replace the entire Power PCB Board Assembly and not the component. There were two part numbers on the assembled board (BN97-00457E & BN94-00622E). After searching online I also found a suitable replacement number for these (BN96-04896A). I found two places who claimed to have the part or have it on order (shopjimmy.com and vancebaldwin.com). After placing orders with both and having neither come through, I broadened my search and found out that the LNR409D was basically the same model as my LNR408D so I looked for its Power PCB Board Assembly part number which turned out to be BN41-00521B. Google search for that part number showed the item available on ebay. I bought it a week ago (ebay 260311519904) for $144 plus $12 shipping. I removed the bad board an hour ago (6 screws about 7 connectors) installed the new one, plugged in the connectors, replaced the covers, plugged in the TV... AND IT WORKS!
Suggestion: If your TV is out of warranty then open it up (what have you got to lose) and see if the problem is obvious and maybe something you can fix (replace) yourself. The parts, spare boards, etc. are out there if you look.

SOURCE: how hard it is to replace by yourself main board Samsung LN-T4065

You need to do some more diagnosing of the problem. If you get sound and change channels take a bright flashlight and place it again the screen. Look for an image around the edge of the flashlight.
If you see an image that means the LCD controller board (TCON) is probably good.

The problem is probably one of three causes;
1) Inverter board is bad
2) CCFT (cold cathode fluorescent light) are bad.
3) Power to the inverter board is bad. You can also check the connectors.

SOURCE: have picture lose picture tv turns off and on

the lamp has a life cicle. if yours is been used a lot. then the lamp has to be changed. when the tv cannot turn on steady and gets off imm. the computer inside the tv tries to turn off the set but the lamp charges again and the micro tends to keep working. the first step to take in this tv is to change the lamp to eliminate this common source of problems

SOURCE: I have a Samsung 56"

Actually the Samsung model you have was the first model to come out in 2006 that did not have a color wheel. The LED blinking is actually a self diagnostic program of sorts. Depending on which lights are blinking, and how often, the service manual will tell you where you should start checking or replacing parts and assemblies. I do have most of the codes, so can you tell me if the if the LED light is the only one flashing, how long it flashes, and do any other lights flash at all? Thank you.

SOURCE: Samsung PS42B430 42" Plasma tv. LED flashes and

The tv power supply board have more dead components parts,u just don't have the skills an the know how to trouble shoot find out more dead components parts that all.Try website like Ebay.com to buy a whole refurbish power supply board for the replacement.