Samsung UN50NU6900BXZA - Boot loop with backlight, no video

[TVAddict]

Hi everyone, so as the title says i have a 50" Samsung tv that boots repeatedly with a quick backlight turn on then off with no video what so ever, no logo, no chime on sound either.

I have been reading a few of the threads that had similar problems to mine and i have decided to go ahead and try a few of the suggestions from those threads (with nothing to lose in mind).

So without writing a novel, i'll try to keep it simple, ALL power supply voltages both to the mainboard and backlight's seem ok and stable, so it lead me to the mainboard where i disconnected one of the LVDS ribbon cables and tv came on and stayed on with full backlight but no video (as you will see in pic1)

So i said to myself, great something to do with either on the panel side or the mainboard side,so hooked it back up and tried disconnecting the other LVDS cable only to have the same result,I was expecting to maybe see at least half a picture or something maybe even lines of some sort but nothing..?
Hooked back up both connectors and back to square one - the initial problem was back.

With no Scope to check signals from the mainboard, i checked for shorted caps, diodes and open resistors on both panel driver boards,nthing turned up, with no information with respect to panel voltages, ckv voltages or testpoints,this is where i threw in the towel, i came to the conclusion that it's either the mainboard or the panel, i guess the only way to find out(in my mind) is to replace the mainboard.

I know i'm greatly lacking vital information/details but if any one has had this particular issue and care to shed some light or maybe point me in some direction where i can have information to try further trouble shooting this problem i would be most grateful and thanks for taking the time to read this.
I was hoping this wouldn't turn into a novel but it still did, LOL

[dskall]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

You can check lvds signals with a multimeter. you should get around 1.5v.

[nomoresonys]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

I think the UN series has a tendency for the nand on mainboard to go bad or get corrupted, I think the mainboards are pretty reasonable on ebay, mine was. There's a good video on youtube, a guy freezing up his nand with freezespray which let the tv on long enough to do a firmware update, fixed it in his case.

[Diah]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

panel issue.. follow this youtube exactly pin no

[nomoresonys]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

Looks good Diah, I would try that first.

[TVAddict]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

I'll start by giving you the bottom line first, i got picture,however not perfect picture,as you will see in the attachments but it's more than i had before which was nothing LOL.

So firstly, i did more checks as suggested using my meter and was able to get the 1.5 volts measurements from both LVDS connectors, so at this point i was of the assumption that i had signal from the MB, also got 3.3v reading and 0.5v reading ( see pic 1 for pin details ) - NOTE measurements were done with one LVDS cable disconneted and the other connected as TV would not remian on long enough to take measurements with both lvds connected.

So now armed with this info and together with the last two post's by Diah and nomoresonys i pressed on, i tried the method in the youtube vid but it didn't work,(head scratching) so logic and some reasoning made me try it on the other side, that's when the magic happened and the picture popped on, i used paper instead of tape so as not to dirty the contacts with sticky residue,because it was a bit of trial and error to find which pins to block,you will see in the pics below, the result was not as perfect as the youtube vid the picture would come up half screen first then full screen with lines in the middle and bottom as you will see in the pics, guess my panel is really screwed,but nonetheless i have some picture and i know the problem is the panel,i now know where i stand with my tv,glad i didn't have to buy a MB to find this out.

One thing is bugging me though, out of curiosity, lets say i have a perfectly working TV, this very model, what would happen if i disconnected one LVDS cable, would i have half a picture or would i see nothing at all??

Huge THANK YOU to dskall, nomoresonys and Diah who replied, you're wisdom and guidance is truly priceless,would not have gotten this far without your HELP this forum kicks butt..

[dskall]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

With a working TV you should get half a picture with one disconnected.

[nomoresonys]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

I think if you block the right line/lines you will get a good picture with no distortion or lines on the screen, recently saw a youtube video, where the guy got it down to one line by using tape and blocking or allowing one clock signal at a time.

[nomoresonys]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

There it is, this guy knows what hes doing, very smart: https://www.youtube.com/watch?v=pfrRhw7-ZII

[TVAddict]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

Thanks again guys for your feedback, i agree that guy in the YT vid sure knows a lot, very informative explanation, so far i see my tv is still showing, i will try to see if i can get it down to as minimal lines as possible, cheers.

[DXseekerMO]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

Thanks again guys for your feedback, i agree that guy in the YT vid sure knows a lot, very informative explanation, so far i see my tv is still showing, i will try to see if i can get it down to as minimal lines as possible, cheers.

If it were me, I'd be removing the outer bezel from the TV (that goes around the screen) and check the screen for a chip/crack on the sides of the screen. If none were found I'd then be checking the flex tabs and embedded gate driver IC's on the sides of the screen for signs of being overheated.

I don't specifically remember if all TVs of this model have side drive tabs. It just so happens I have this specific model apart right now with the side drive tabs exposed.

[TVAddict]

Re: Samsung UN50NU6900BXZA - Boot loop with backlight, no video

If it were me, I'd be removing the outer bezel from the TV (that goes around the screen) and check the screen for a chip/crack on the sides of the screen. If none were found I'd then be checking the flex tabs and embedded gate driver IC's on the sides of the screen for signs of being overheated.

I don't specifically remember if all TVs of this model have side drive tabs. It just so happens I have this specific model apart right now with the side drive tabs exposed.

Thanks for your suggestion DXseekerMO and i hope you are successful with the one you're working on as you said,but i've already closed mine back up and i'm not thrilled in the least to pop open anything on it again, it sure was a pain to safely pop those clips all the way around that back cover, but besides the obvious, changing the panel, can anything actually be done if it did have a chip/crack or if there were some issue with the flex tabs, and if it didn't have any chip or crack i think i would most certainly give it one in removing that bezel

I guess either way my panel is more or less toast,the way i figure it's just a matter of time before i get more lines or lose the picture again.
So it's working good enough for me now, hopefully it can go a while until i can replace it.
Despite all this i'm happy to have been able to troubleshoot the tv with help from you guys