I have a Samsung UN55J620DAFXZA 55 LED TV with black screen w/sound. blue lite on tcon board when powered.LED strip bad?

The main board and the power supply is bad for your TV and it would be more easier to buy a new TV than to try and fix the current TV that you have and that our TV could of had died on you.

Inmost of the case,the problem is the LED strips.

To check it, the best way is use a LED tester, if you do not have one, you have to disassembly the LCD panel, unplug the cable between the power supply & the main board, apply the AC power to the TV, you will see the defective strips do not light up.

I saw a similar problem reported on "fixya" for LED monitors that suggested looking at the capacitors on the circuit board to see if they have erupted or popped. The capacitors look like little cylinders and if failed, their three flaps on the top will open up slightly. Replace the capacitors in this case. If too difficult to solder them, might have to replace the whole strip containing them.

Mostly is the LED back strips.

in most of the case, the problem is defective LED back lights strips.

1. Disconnect the cable between the main power supply & main board, supply AC to the TV, if the LED strips are OK, it should light UP, if not replaced all of the LED strips.
2. If the back lights light up, but no display or sound, replaced the main board.(after you re-connect cable).

You will need the board to talk to the led strips. They dimm and bright as the brightness of the video controller changes.

You have at least one bad LED in the panel and its shutting down the power supply...for future reference a bad Tcon will not cause loss of sound only affects picture

You're a technician work to earn I assume. Do understand; this is a forum to help one who knows a little; to make their sets right. Not a help you like people to turn revenue out of it. Understand? Do not know nothing; yet runs a service shop to cheat others!!!!! https://electronicshelponline.blogspot.com/

perhaps the backlight invertor driver circuit.

Samsung TV Repair Part Number Identification Backlight Inverters LED...
See where the wires from the long LED strips on the both sides of the screen lead you to.

does your model have separate board for backlight ? or is it integrated with TCON ?