When first turning it on, the TV will flash the LG logo very quickly and then it goes black. I can do the flashlight test and see the menus. I have replaced the t-con board and the power board.
You have bad LED backlights, it's unfortunate that people change boards not knowing anything about how a TV works, such a waste of money and time. Of the LG sets I work on with your symptoms 95% of them are backlight issues
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/
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.
Fault to the main power supply regulator section. Either it will be a separate board, or the part of 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.
SOURCE: lg led tv backlight
Fault with its main board. Short circuited component/s at it. Contact any service technician; or the authorized service center. 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/ . In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.
SOURCE: How do I determine if it's the LED Driver or the LED lights that are bad on my LG LED TV?
If it was the LEDs, then you should still have some working. My first thought would be the LED driver circuits.
Best of luck.
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I'm not finding a main board in stock anywhere. The LED driver is built into the power supply board (from what I can tell).
Replace all LED strips. May be some of them changed its activation voltage and then it don't pass the startup circuit test, so the LED set will not light.
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