Samsung UE55NU7025K not starting/looping

[nebula]

Hi all, I have a Samsung 55" with a startup problem, backlights light up and there is an attempt to show a picture but it turns off, flashes 3 times on power LED and tries again to start. When I remove one of the T-Con flexes I can hear the startup sound but nothing appears on the screen apart from the backlights turning on, same happens each side. I cannot see any damage to the T-con strips so I am not sure at this point if the problem is Mainboard or LCD panel.
The customer claimed the TV just stopped showing a picture all of a sudden.
Any help would be highly appreciated.

Main/Power board is BN9646822A - Panel is CY-NN055HGLV6H

[Davi.p]

Re: Samsung UE55NU7025K not starting/looping

locate on the panel's distribution boards an eventual short circuit on caps/diodes

[nebula]

Re: Samsung UE55NU7025K not starting/looping

Tested all caps and diodes on both boards, nothing was short or damaged. Not sure where to look now.

[yokoono]

Re: Samsung UE55NU7025K not starting/looping

If you don't have an image on half the screen when you disconnect a ribbon, it means that the protection comes in at the t-con. To see which part of the screen has problems, you must cancel the t-con protection.

[nebula]

Re: Samsung UE55NU7025K not starting/looping

This is an all-in-one board with PS, Main and Tcon on one PCB. I can't find anything relevant to this type of board online, just videos in hindi for common T-Con boards.

[Davi.p]

Re: Samsung UE55NU7025K not starting/looping

the panel's load can lighten the power on the supply rail that feeds the leds driver i guess, so a difference in current can make a faulty led to work or not..

[nebula]

Re: Samsung UE55NU7025K not starting/looping

OK so you are suggesting the problem lies with the board and not the panel? I don't want to risk replacing the board only to find that isn't the issue.

[Storyteller12]

Re: Samsung UE55NU7025K not starting/looping

Try taping some pins going from the board to the panel. See if you can get it to stay on or show a picture. If so then it’s the panel. If not possibly the board

Have nothing to lose at this point. Honestly this model is trash and I wouldn’t put any money into it. If you can fix for free great, if not trash it

[Davi.p]

Re: Samsung UE55NU7025K not starting/looping

No i mean bad leds..

[comptek]

Re: Samsung UE55NU7025K not starting/looping

Disconnect power supply from Mai board backlights should fire up ok
Disconnect main board to screen bothe lvds cables see if it boots properly if it does panel is shorted, use tape to insulate lvds top five or six traces of the top lvds cable is a good start

[nebula]

Re: Samsung UE55NU7025K not starting/looping

I already stated in my first message that backlight isn't the issue... with either one of the flex going to T-Con connected it boots as I can hear the startup chime, with both connected it reboots. I'll reassemble and return to the customer as I'm not prepared to spend time or money on it just to find out the panel is bad. Thank you everyone for your input and time.

[DarkoOhrid]

Re: Samsung UE55NU7025K not starting/looping

I have the same problem.The problem is panel.When I disconect any flat from T-con,the tv starts and I can hear audio.When the connect both flat cable from T- con the tv restarts.

[nomoresonys]

Re: Samsung UE55NU7025K not starting/looping

right on both tvs, panel problem.

[howardc64]

Re: Samsung UE55NU7025K not starting/looping

If panel distribution board has shorted rails (by testing both side of caps for continuity), then thermal cam + voltage injection can find it. Recently fixed one like this.

https://www.badcaps.net/forum/showpo...2&postcount=86

[Davi.p]

Re: Samsung UE55NU7025K not starting/looping

usually there's no need of expensive thermal cam, it is enough an average dmm, when short is complete, but the OP said no shorts..

[howardc64]

Re: Samsung UE55NU7025K not starting/looping

usually there's no need of expensive thermal cam, it is enough an average dmm, when short is complete

Interesting, whats the technique to find the specific shorted cap with DMM? I'm only aware of voltage injection with ISO / flux / thermal cam but am not a professional. Got the used 1x thermal cam for $60 as I see micro-soldering repair techs use it all the time on phone and laptop boards.

but the OP said no shorts..

Yes, OP found no shorts in post #3, left the note for poster in #12

[nomoresonys]

Re: Samsung UE55NU7025K not starting/looping

you are absolutely correct Howardc64, a thermal camera is a very good investment and can find shorted components very efficiently.

[Davi.p]

Re: Samsung UE55NU7025K not starting/looping

Hi, very simple, use the DMM as the milliohm meter, only take notice of the decimal part, the integer one is obviously zero, dont use less than about 15$ dmm, the cables should be thick enough, no kids games..

[nomoresonys]

Re: Samsung UE55NU7025K not starting/looping

sure its that simple, thats why there's like 100 videos on youtube about how to make a miliohm meter right, BECAUSE they just aren't needed, NO its not a kids game, that's why intelligent grown up people are making and usuing them.

[nomoresonys]

Re: Samsung UE55NU7025K not starting/looping

some show how to make a fairly simple circuit to turn a cheap multimeter into a miliohm meter, needed if your meter lacks miliohm function, not a matter of moving decimals, which is hilarious btw...LOLOLOL.