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Thank you for posting your question on Just Answer! I will be happy to help you with this problem.
Well friend what causes this is a bad coil or capacitor, usually on the power supply, and possibly on the backlight inverters. If you turn on unit and it doesnt have the high pitch, then main suspect is the main board, but if you are still getting the pitch, my trick is to use a can of cold spray, and hit all boards until you find the pitch, and thats the board you will need. because the change in temperature will expose the bad part.
Well Good luck friend.
You will have to replace, the main board is full of digital and logic circuits. but check with manufacturer or list below for best price. And yes a average joe can repair it