Samsung tv backlight problem

Based on the symptoms you described, it sounds like the problem is likely with the LED backlight strips on your Samsung TV model DF400BGLV1H. When you disconnect the LED connector, the standby voltage comes back, and the T-CON board blue LED lights go on and the boot sound. Also, the fact that the power supply board measures 225 volts on pin 1 and 2 of the D+ on the connector when disconnected and toggles off when connected to the LED, suggest a short on the LED side.
It is possible that one or more of the LED backlight strips may have failed, causing a short and preventing the TV from powering on properly. In this case, replacing the LED backlight strips would be the most likely solution to the problem.
Keep in mind that it is always a good idea to double-check all connections and components for proper function and continuity, before replacing any parts.
It's recommended to seek the help of a professional technician or contact Samsung customer service for further assistance, especially if you are not familiar with TVs. Also, make sure you get the right replacement parts and follow the instructions.

Hi Ashley....Chances are your LED backlights need replacing, if you see a flash then black screen some of the lamps are shorted and the current draw is too high, and the protection circuitry is shutting down the inverter. You can check to be sure the main is working by testing the backlight on pin on the plug that goes from the main to power board, you need to see 3.3 vdc on that pin when you power the set on and it needs to stay at that voltage or you have main board issues

The back light and the screen has stopped working and needs to be replaced and the power supply is no longer working and also needs to be replaced as well.

This model set had some issues with the backlight driver connector solder joints, make sure those are ok first, it they're ok it's a backlight issue

Use a voltmeter to confirm all the voltages are present when the TV is powered on. If they are all correct then replace the led driver.

Do flashlight test - if you can see image you need t con board. If no images seen, inverter board. TV Parts Universal TV Stands DLP Chips ShopJimmy

In most of the case, the problem is the LED back lights strips, it was the most case we encountered.
To check it, un-plug the cable between the power supply & the main board, apply the AC power to it, if the back lights came on, replace the main board, if not, mostly the problem is the back lights LED strips.

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 board.

T con board issue.

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.