samsung NU7100f - audio no video

[benareeno]

Hi all, first post here. I hope many more to come and I hope to become a resource for others in the future. As for now..I need your help

I have a 43nu7100f and it powers on and I can cycle the inputs...but the screen is completely black.

I did the flashlight test and as far as I can tell, there is absolutely no backlight action going on here. I took the back of the tv off and still don't see any light coming through.

I also notice that there is a very quiet, yet audible screeching or some sort of noise coming from the power supply board. It's almost like there are mice in the tv (there are not). It's like a high pitched squeeling but it's not loud. Many would not hear it.

I inspected both boards and don't see any obvious solder cracks, etc. Any thoughts on my next steps?

Thanks in advance!

[RDC55]

Re: samsung NU7100f - audio no video

Samsung made it easy to test the backlights and power supply. Try disconnecting the cable that goes from the Power Supply to the Main board and when you plug the TV in the backlights should come on.

An audible sound may indicate an issue on the SMPS as the normal frequencies are well above human hearing.

Posting pictures of the back side of the set showing the interconnect as well as individual boards is almost always helpful.

[benareeno]

Re: samsung NU7100f - audio no video

ok...unplugging that connector did not allow the lights to come on. Or perhaps I'm missing a step. In fact, unplugging that connector makes the standby light go off. It also stops that squealy sound. Remember, the sound is quite faint, but it is there. And leaning in, I think that squealy sound is coming from the system board.

Do i unplug the connector when power cable is unplugged and then plug in power cable? That is what I did...

Pics to follow.

[benareeno]

Re: samsung NU7100f - audio no video

Pics

[benareeno]

Re: samsung NU7100f - audio no video

perhaps I need better pics here, just let me know.

[RDC55]

Re: samsung NU7100f - audio no video

"I did the flashlight test and as far as I can tell, there is absolutely no backlight action going on here. I took the back of the tv off and still don't see any light coming through"

The flashlight test is done from the front of the TV and it enables you to see video when the backlights are not working. You need a fairly bright light, and normally what you see is the power up logo.

"Do i unplug the connector when power cable is unplugged and then plug in power cable? That is what I did..."

Yes, that is correct and yes the picture is too blurry to reference the cable connector, but I suspect you got the right one.

So, I would suggest doing the flashlight test again and report back on that.

You could also go ahead and with the connector unplugged measure and report the voltages on that connector - they are measured in respect to chassis ground.

And a word of caution - the hot side of the board contains some dangerous voltages so be careful what you touch. The large capacitor on the hot side can also maintain a charge so even when off be careful on handling the board and try not to touch any electrical connections, which should be done anyway as much of the board is static sensitive. Reconnect all the cables and unplugging the TV and letting it sit a few minutes will usually drain those areas.

If you have a backlight tester knowing that a Samsung should have backlights with the cabe disconnected I would test the backlights.

[handsworth]

Re: samsung NU7100f - audio no video

I would suspect backlights also. I've repaired many of these "NU" series Samsung tvs with new backlights. There are 2 strips at the bottom of the screen and both could be blown. You have audio and the inputs cycle, so I would rule out the main board. You have standby light but by disconnecting the main from the power supply the leds should come on. When you do the flashlight test, use a bright light and look for the Samsung logo right in the middle of the screen.

[DXseekerMO]

Re: samsung NU7100f - audio no video

perhaps I need better pics here, just let me know.

Before ordering backlights for this TV there's something you need to know:

Often times these backlights get very very hot, enough so to cause the main diffuser to melt and/or crack. Before ordering parts it would be wise to disassemble the TV and make sure the main diffuser isn't cracked or melted on the bottom. If it is these defects will show up on the picture after installing the backlights and will affect the picture in a very displeasing way. I don't consider the TV usable/sellable with these issues.

Finding a main diffuser will be just as difficult as finding a screen for a busted screen TV.

[benareeno]

Re: samsung NU7100f - audio no video

RDC55, I did the test from the front...but in a dark room, with the back of the tv off, you can also see the backlight (as I saw in a youtube repair video). I was just saying...no light in that situation either.

Ok...I guess I need to take apart the tv further to look for more damage. But I do suspect the LED's for sure.

Do I really need to order the backlight tester or is there a way to test with normal tools?

Also, I'll redo the flashlight test with a brighter light.

Thanks for the inputs!

[benareeno]

Re: samsung NU7100f - audio no video

no pun intended!

[benareeno]

Re: samsung NU7100f - audio no video

Before ordering backlights for this TV there's something you need to know:

Often times these backlights get very very hot, enough so to cause the main diffuser to melt and/or crack. Before ordering parts it would be wise to disassemble the TV and make sure the main diffuser isn't cracked or melted on the bottom. If it is these defects will show up on the picture after installing the backlights and will affect the picture in a very displeasing way. I don't consider the TV usable/sellable with these issues.

Finding a main diffuser will be just as difficult as finding a screen for a busted screen TV.

Huge point!! I will get to this...is the main diffuser a layer under the outer screen?

[handsworth]

Re: samsung NU7100f - audio no video

The diffuser that burns is the thicker clear piece of plastic. If burned, you will see it immediately. If not burned too bad, I turn it around so the burns are at the top now. 180 degree turn, not flipped. The bezel will usually cover it.

[DXseekerMO]

Re: samsung NU7100f - audio no video

Huge point!! I will get to this...is the main diffuser a layer under the outer screen?

It is behind the screen and the "soft" diffusion layers. The LEDs shine directly in to it.

The diffuser that burns is the thicker clear piece of plastic. If burned, you will see it immediately. If not burned too bad, I turn it around so the burns are at the top now. 180 degree turn, not flipped. The bezel will usually cover it.

This appears to be a GENIUS SIMPLE solution, but how does the picture look with this workaround applied? I don't guess you'd have a photo of how the picture looks after doing this? I was under the impression there are coatings along the edge of these diffusers that didn't make this possible?

[handsworth]

Re: samsung NU7100f - audio no video

Attached is a pic of a bad diffuser with led burn marks all the way across. Obviously I'm not using it anymore because of the cracks. The 2nd pic is a UN55NU7100 that I have up for sale now. The difuser had similar burns so after replacing the leds, I just turn the screen around. The bezel, soft diffusers and screen will hide any marks or shadows.

[DXseekerMO]

Re: samsung NU7100f - audio no video

Attached is a pic of a bad diffuser with led burn marks all the way across. Obviously I'm not using it anymore because of the cracks. The 2nd pic is a UN55NU7100 that I have up for sale now. The difuser had similar burns so after replacing the leds, I just turn the screen around. The bezel, soft diffusers and screen will hide any marks or shadows.

That is AWESOME! Genius!

[neilc6]

Re: samsung NU7100f - audio no video

Good to know you can turn the diffuser sheet around. Bad that it can also crack from the heat. The one I repaired wasn't melted luckily.

Previous thread here https://www.badcaps.net/forum/showthread.php?t=93035

[benareeno]

Re: samsung NU7100f - audio no video

Attached is a pic of a bad diffuser with led burn marks all the way across. Obviously I'm not using it anymore because of the cracks. The 2nd pic is a UN55NU7100 that I have up for sale now. The difuser had similar burns so after replacing the leds, I just turn the screen around. The bezel, soft diffusers and screen will hide any marks or shadows.

Was your 7100 having the same symptoms as mine? And the fix was replacing LEDs?

[handsworth]

Re: samsung NU7100f - audio no video

"Was your 7100 having the same symptoms as mine? And the fix was replacing LEDs?"

Yeah, leds were the problem

[benareeno]

Re: samsung NU7100f - audio no video

"Was your 7100 having the same symptoms as mine? And the fix was replacing LEDs?"

Yeah, leds were the problem

cool...so, did you replace entire strips...or just test the leds individually and replace them as needed?

and does that mean your tv showed an image on the flashlight test?

[neilc6]

Re: samsung NU7100f - audio no video

Replacement strips are only like $20 USD. LEDs wear just like like bulbs and if you don't want to take apart your TV every few months, replace them all with new.

https://techhometravel.com/lg-ln-ser...ed-backlights/
https://techhometravel.com/samsung-n...ight-failures/
https://techhometravel.com/samsung-u...t-replacement/