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Samsung TV has Power and Sound but Black Screen

I have a Samsung TV (Model # UN40JU6500F) that has sound but a black screen. At first I thought it was the LED backlights so I changed those out. This didn't solve the problem. When I held a flashlight up to the screen (while the TV is supposed to show a picture) I didn't see a faint picture either. I think my issue is either the bus that the LED light strips plug into, the power supply, or the screen itself. How can I narrow down the options?

Update (08/03/23)

Sorry for the long wait. It turns out the problem was the TCON board. I replaced the main board and still had the same problems. Replacing the TCON board fixed the problem. The F200 fuse on the TCON measured 12.8V so it was still getting power. Something else must have happened to it. Thanks everyone!

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Sorry for the long wait. It turns out the problem was the TCON board. I replaced the main board and still had the same problems. Replacing the TCON board fixed the problem. The F200 fuse on the TCON measured 12.8V so it was still getting power. Something else must have happened to it. Thanks everyone!

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Hi @toastertom

With the TV on but no image check if there is 12V on both sides of the fuse F200 on the tcon board.

If not given that there is also no backlights its looking like the mainboard.

If the fuse is blown then more likely it is the tcon board

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I used the "10 MegOhm input DCV" setting on my multimeter. The voltage is around 12.88V.

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And I measured the fuse when I had the screen on.

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I also saw a blue light on the TCON board light up for a second when I plugged the tv into the outlet. (The light is in the upper left of your full-board picture.) I don't know if that is any helpful information.

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@toastertom

Not sure about the tcon board light but if the voltage stays on the fuse all the time that the TV is on then the tcon is getting power.

Since there are no backlights and the power for the backlights comes from the mainboard I'd be suspecting the mainboard as it controls the power and signals to the tcon and also turns the backlights on and off.

Also with regards to the blinking TV power light, Samsung have never said what their TV power light blink error codes mean or not that I've ever come across anyway. Even in some of their TV service manuals that I've seen, it is not mentioned. If you find out let us know ;-)

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If you do not see any video with a flashlight then it isn't a backlight problem, it is a video problem.

It is more likely a TCON board or possibly the main board supplying video to the TCON board.

TCON boards are high power devices so they are the more likely to fail.

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Is there any way to narrow down if it’s the main board or TCON?

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If you have an Oscilloscope, you might be able to trace a video signal. Some TVs will flash the power LED to give you a clue as to where the problem lies. Troubleshooting is a matter of observing everything the UUT is doing, but if it isn't giving you other clues then the only option is part substitution. My Pana gave me the 7 flashes of death which pointed to the TCON board and I was able to replace all the bad MOSFETS instead of changing the whole board. If you can find a service manual, it may have a procedure to isolate the problem.

This might help

https://www.samsung.com/ca/support/tv-au...

This one might be similar enough

https://www.manualslib.com/manual/147153...

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The power LED is giving me 5 flashes when I turn the screen on.

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@toastertom Samsung never published any information regarding the POST blink codes. 5 blinks are commonly caused by a bad power board. I would suggest that you start with disconnecting the main board from the power board and see if that turns your backlight on. If it does, you can be reasonably assured that this is not your power board. Of course, you can also measure the voltages going from the power board to the backlight strips and see what that voltage is. Check the diodes on the power supply. Make sure those show the proper values. Also, there should be two LED's on your T-con board. If both are off your T-con board has issues with the DC supply. Once you checked all of these you can then deduct which board has failed. My first suspect is the main board as well. Let us know what you find.

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I replaced the main board to no avail. There was no change at all to the listed symptoms. I haven't checked the diodes on the power board (This is my first time trying to repair a tv and wasn't comfortable messing with the live power board).

My new line of thinking is either the TCON board (which has one light turn on for a sec when connected to power),

the FFC cable from the main board to the TCON board (although I'm measuring 12.8V on the F200 fuse on the TCON board),

the power board itself (although when I disconnect the main board, I'm getting all of the LED lights to turn on),

or the cable that connects the power supply to the main board.

Any further info would be appreciated!

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@toastertom check the components as functions and try to fix your TV based on those outcomes.

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I have sound and no picture with blue screen. I do get a picture in the upper corner when using the guide but when I go to full screen it goes blue. Jtp

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@jackieparcell

What is the model number of the TV?

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