No picture no sound when tv is on 42lb9df-ad no picture and sound when tv is on

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That problem is usually have 2 causes..Its either power supply board or main board..

Please take this steps on how to determine the problem:
1. Open the back cover.
2. Check the power supply output...It should have 5vdc for the main board..12vdc or 16vdc for the audio and 24vdc for the back-light inverter..
3. If those 3 voltage supplies have encountered voltage drop...The problem could be on power supply board..
4. If the power supply output is normal..The problem could be on the main board...
5. If the problem is power supply you should check if the capacitors are bulged on the top and try to replaced it..If you can't do that you can purchased new power supply board..
6. If the problem is on main board there is no D.I.Y repair on that so you need to buy a new main board that fits to your TV..
Hope this solution will be helpful..

Thanks for using fixya...
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