I have replaced the Power Supply Board, and Both of the Main Boards. At first it would not power up, and the LED would burn constantly. The SEARS repairman replaced the Power supply and the board next to it. Afterwards he showed me what looked like water stain on the A board, and said it was too costly to replace this board. I ordered a replacement board from the same place he picked up the last board and power supply from. Now the TV Powers up great. It has a great picture but no blue projector. The LED now blinks five blinks repeatedly.

Depending on the model maybe. Tv's like all electronic items use multiple circuits that are interconnected. So if you have a problem like you described it can be any interconnected board. I experienced problems like you described many times. Use your eyes and nose. Turn off the power, remove all boards and visually inspect. While boards are out sniff each board. Look on both sides of each board. If nothing is found I would start with the power supply and replace it. You can check the output voltage where the power supply connects the the main board. It is harder to check the main board function because the signals pulsing thru the main board require specialized equipment.

If you wish to get some details; visit the site linked here. Pull up older posts.
https://electronicshelponline.blogspot.com/
faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent.
Search the site by type in the "BRAND NAME" of your device; (Exclude the model number), in the "Search box at the top right of the display window of the Homepage" to get gathered related posts/

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main digital board.
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And all the Capps are down on the rest of the boards also it a switch mode power supply so make sure it's switching

If you have the 5.3 standby it's the (main board)....sometimes when the main is shorted you won't have your 12 volt supply...

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
www.electro-medical.blogspot.com
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement
also check the video

Fault to the main power supply regulator section. Either it will be on a separate board, or on the part of its main board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electronicshelponline.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

Fault with the main power supply regulator section. Either it will be on a separate board, or on the part of its main board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electronicshelponline.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main digital board.//

Without any error codes hard to say. I would check the power supply for any swollen caps and replace them. Start checking voltages. Check for voltages to the inverter boards. Unplug the tcon board and see if unit will power on. The main board gets a constant always on +5v from power board.When power button is press a turn on voltage is sent from main to power board. Unplug inverter boards and try to turn on. Inverter boards are just a high vol ballast the supply voltage to the florencent back lighting.