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Samsung 75" TV UN series.

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Samsung TV UN75NU rebooting with click

HI Guys,

A few days ago I started experiencing Samsung UN75NU800DF rebooting issue and I am hoping someone can help.

This 75" UN75NU800DF is 5 years old and started to reboot itself, like turning on then off with a relay click sound. After some google and youtube I tried some troubleshooting.

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I removed the back panel and checked the power board for any irregularity, and the capacitors and solder joins look fine. I then disconnected the ribbon cable between the power and main boards and powered on the tv. Clicking stop and backlight stayed on.

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I then tested each pin out for the ribbon cable with a digital meter and the output voltages match to the pinout diagram on the power board (13v but tested to be around 12.8V). At this point I am thinking the power board is working OK.

Next I tried removing each of the two ribbon cables between the main and the LCD boards (labeled 1 & 2 in the photo below) in turn to test if it's LCD problem. First the top cable is removed (the bottom is still connected to the main board) and powered on the TV. The TV turned on, sound is on, remote is working, backlight is on, but no picture. Then I did the same for the bottom ribbon cable while leaving the top cable connected, same thing happened. Finally I disconnected both the ribbon cables and again, sound, backlight, remote are all working but no picture.

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Finally, I reconnected everything back to original and sure enough, the TV went back to rebooting and clicking.

My question is what can be the issue? The power board seems to be working, backlight stays on if not connecting to the main board. Can main board be the problem? Or is LCD driver board the issue and I nees to try the tape off method?

Thank you very much.

Update 10/9/23

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The connection where the ribbon cables terminate is shown below:

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It's showing the area of the incoming power cable connector and first ribbon cable to the LCD board

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@eddiewang76529 excellent troubleshooting. The clicking commonly happens with a bad mainboard. Yours is more complicated since you get the signals except video. The problem is that your T-con circuit is on the mainboard. If you can, try to rake some good images of the mainboard. It’ll have to be focused and large enough yo zoom in to the components and the reference designators ( if this board has them). We’d be looking for Vdd, Vss and other test-points. Also, there should be a 12v line going to the panel. If the test-points are there and if the voltages are right, then a Tape-off can help. Remember that even a tape-off only works about 75% of the time.

Add a picture of the connectors where the two ribbon cables terminate too. Lets see what that looks like.

Update (10/09/23)

@eddiewang76529 check the few components I marked with some blue arrows. Check for continuity and voltage (VDC). You'll have to test those with your TV "on" so be mindful of the power board etc. Use your probes to touch things on the board, not your fingers :-) At that point it could be a shocking experience. So, use caution and consider your power board will bite.

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12 Commenti:

@eddiewang76529 looks like there are test-points on the bottom right quadrant of your first picture. Possible to get a more focused image of that area?

da

@oldturkey03

Thank you. Since Comment does not allow pictures please access via this link

https://www.dropbox.com/scl/fi/u0z7s8jft...

It's showing the area of the incoming power cable connector and first ribbon cable to the LCD board

da

@oldturkey03

Thank you very much for the input. I tried to look for Vdd, Vss and 12V on the main board but I have no luck pinpointing them, can you tell me which area I should be looking at? Below are two photos of the main board, one shows top half and the other bottom.

[image|3097685]

[image|3097686]

The connection where the ribbon cables terminate is shown below:

[image|3097688]

[image|3097687]

Again appreciate your help.

da

@eddiewang76529 We got that taken care off, now let me see if I can find the test-points we need to determine what's broke (or at least come close ;-)

da

@eddiewang76529 Picture number 7 bottom L corner looks like a ribbon cable. Does your panel have more than 2 driver boards? Are those connected via ribbon cables as well? If so, repeat your test but this time disconnect each one of those. power off, disconnect ribbon cable, power on retry. Power off, reconnect, disconnect other side, power on, retry.

Still checking the main board for any hint of the right test points. Darn, getting old. that writing is freaking small :-) "I'm so mad I'm getting old It makes me reckless"

da

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Eddie Wang sarà eternamente grato.
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