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T-CON stands for timing controller and it wont affect the audio. You have an issue with the main board.

Check and clean all of the wiring harnesses and ribbons for good, tight connections. U have already replaced the main and t con boards

This is often caused by the Y-sustain board, be careful to drain all power before undoing the ribbons and are all secured before testing with power, I blew my whole board this way.

Power Issues Troubleshooting
*NOTE* LG & Vizio TVs must be plugged in for 5 minutes before it will turn on*
1. Inspect ALL Ribbons and connectors. Any tears or bad connections between boards must be replaced FIRST
2. If you have any of these boards, it should be the first board to be replaced
A) T-Con Board - Video Problems (No Video with standby light on, audio but no video, grainy, distorted, or color problems in screen)
B) X or Y Buffer Board (Plasma TVs only) - Standby light is on but no power
C) Backlight Inverter / LED Driver - No Video with standby light on
3. Main Video Board
- Standby light is on but no power
- Either video or audio does not work (if no T-Con in TV. If audio but no video it is T-Con)
4. Power Board - No power AND standby light does NOT turn on. If standby light is on try other boards above
5. Panel - No power, distorted picture, lines, slow motion, half screen, faded in / out. Panel problems are usually not worth replacing the panel.

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://electro-medical.blogspot.com/
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 board.

Hi, maybe before replacing T-Con board it should be better to check voltages from power supply to the board, you could google for the service manual of your TV to have the right values of voltages and the signals you could check.

Sounds like main power regulator board fault. Contact the authorized service centre to buy a genuine board; or 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.

If the replaced T-con boards are working boards tested on another system then the fault is not where it is suspected.
It is important to take a signal and voltage check on the RF inputs so as to trace the signal path or if there was a power loss to the board , in which case the fault can be the power supply unit.