Samsung GU50TU8079U bad panel diagnosis

[Ierwin]

Hello,

I was given this Samsung GU50TU8079U that would power cycle after a couple seconds, sometimes a few minutes. The screen would turned cloudy dark with the backlight still lit and then the sytem would restart.
Its one of the newer screwless Samsung models that I read a lot about panel failures here. It does not have a sperate T-CON board, just one ribon from the mainboard to the panel board and a U-shaped ribbon cable connecting the other half.
I went through the usual diagnostics:
unplugged the mainboard -> tv stayed on
removed the U-Shape robbon -> tv stayed on

I then started to tape off pins of the ribbon between the halves.
It was a lengthy procedure to play with the tape because the set would sometimes work perfectly fine for 10 minutes before it restarted.
The least tape that I can get the tv to start with results in heavy horizontal lines though, not usable at all.
So I removed all the tape, put everything back together and was about to put the tv in a corner, when it suddenly came on and stayed on.
There was nothing but a single distorted line on the right side of the screen, only noticeable on solid color images.
The tv worked like this for a couple of days.

Then suddenly it turned off and started to power cycle again. This time much faster, restarting right after the program starts to play.

I was wondering if there is anything I can still try before I call it a brick.
Ive read that some people found shorted diodes or caps on the panel boards, but I'm not exactly sure where to look and could not find anything yet.
I would be able to borrow a themal camera too, if that could help diagnose the problem.

Any Ideas are welcome.

[Davi.p]

Re: Samsung GU50TU8079U bad panel diagnosis

in panel stripe boards: test every resistor, if good remove T16, T15 and re test

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

Are t16 and t15 protection diodes? And is there any way to test them before e pull them off, because I won't be able to put them back

[lotas]

Re: Samsung GU50TU8079U bad panel diagnosis

Check these test points with a multimeter for low resistance or a short to ground (GND).

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

Ich checked all the points with 2000Ohm Setting on the Meter.
All were higher except for 2 on the right side.
VGK @530Ohm but only one direction
VSS @1000Ohm

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

I went and carefully checked T16 and T15 again.
There seem to be several shorts across the pins left to right.

Before I rip them off as suggested I would like to undertsand what they usually do though. Could you explan what they are?

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

first clean panel edge boards from the moister you have because of cleaning or water liquid

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

I did not use any water to clean but of course there might be moisture... I could evaporate using a heat gun and just carfully warm it up a little bit?

I also was able to read the marking on T15 and T16: 5R2P so obviously those are esd protection diodes... not saying I know what they are there for

[lotas]

Re: Samsung GU50TU8079U bad panel diagnosis

"removed the U-Shape robbon -> tv stayed on"
Try this.

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

no... never use any heat ... just with cotton cloth and alcohol massage the COF ribbon and the complete boards..
after you do and its clean... just plug out one side the U ribbon " ribbon cable like letter U " you have on each side one a time and plug in see what result you have

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

"removed the U-Shape robbon -> tv stayed on"
Try this.

with the ribbon removed completely the backlight stays on but no picture of course. The tv is currently set to some samsung streaming program via Wifi. The sound is not constantly on but without a picture its hard to tell if there is connection problem with the source or if the tv is not actually fullyfunctional.

I taped the 14 pins and the tv reboots again.
Which is strange because a couple days ago I managed to have it stay on with fewer pins taped but had black lines then.

Will clean with isopropano now

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

dont do any tape.... just do one time for each side u ribbon disconnected.#

did the set stay on and on which side u ribbon disconnected ....

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

dont do any tape.... just do one time for each side u ribbon disconnected.#

did the set stay on and on which side u ribbon disconnected ....

If I disconnect the C-shaped ribbon on any side the backlight stays on.
The sound stops after about a minute but it does not make a difference what side of the ribbon is connected.
with both sides of the ribbin connected the tv reboots right away, most of the time before any sound comes on, or a second after

[lotas]

Re: Samsung GU50TU8079U bad panel diagnosis

On these 14 pins you need to experiment to see what will be best according to the image.

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

On these 14 pins you need to experiment to see what will be best according to the image.

he never have image at any case... but the sound cut down... we have issue on main boards
its sound to me panel esd got defect short then mb suffer at dc dc converter... so it is much u have open r / l some whereon MB

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

hey did you put the set laying on the yours bed so u just notice the sound and back light ... not the screen self ....lol

[Davi.p]

Re: Samsung GU50TU8079U bad panel diagnosis

the 2 center pins are tied together and to gnd, the other pins must not at gnd..

[Diah]

Re: Samsung GU50TU8079U bad panel diagnosis

the 2 center pins are tied together and to gnd, the other pins must not at gnd..

when the demos come , angels flee..

goof luck with yours esd removes LOL

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

hey did you put the set laying on the yours bed so u just notice the sound and back light ... not the screen self ....lol

right now it is sitting face down on my desk on blanket, yes. But of course I lifted it up to check the screen :P

I dont know what has caused this but the behavior now is different from what it started with.
1. When I got the set it rebooted after 2-10 minutes
2. after playing with tape and giving up it stayed on for hours with good picture except for 2-3 tiny lines
3. after a couple days it suddenly turned off and restarted immediately
4. playing with tape again I was able to keep it turned on but there were lines all over the panel (had to tape ~5 pins)
5. now taping all 14 pins is not enough to keep it from rebooting and the sound cuts off after a minute.

I am one step from cominng to the obvious conclusion that this tv is haunted

[Ierwin]

Re: Samsung GU50TU8079U bad panel diagnosis

the 2 center pins are tied together and to gnd, the other pins must not at gnd..

that is exactly what I measure about the GND connection. Only the center pins. No short to GND fro any other pin.