SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

[mnementh]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

you know its sad how we have just accepted the fact that you cant buy a replacement panel from the manufacturer. its the weakest point of the whole tv and when it goes there aint shit you can do. frustrating.

Yeah; it's not so much can't as it is NCE (not cost effective) to repair. Even by the containerload, the LCD panels are the single most expensive part of the TV, as in ~70% or more of total BOM. To the manufacturer, that panel is the TV... it's counterproductive for them to sell that component cheaply enough that you can fix your TV when they can just build a new TV with it for less than the cost of running a parts counter operation.

Add safe handling of a huge fragile piece of glass only a few mm thick, and you're talking the same shipping expense as a whole TV... so in toto with parts counter & inventory expense, getting a new panel to you would cost as much or more than a whole TV.

mnem
*currently battling a 58" onn 4K TV which after 11 months in service*

[Davi.p]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

not all the caps must be removed, only those on 15-17v line or at least on the 8v line

Bought a fairly new Seek Thermal FLIR cam for $60. Injected 1.5V 1A limit on the VADD rail (low enough and no need to cut any panel COF lines for protection) and the shorted cap gradually lit up.

It's highly dangerous to inject the 15v line without other supply lines! There's no need of thermal cam to find the correct bad cap, good DMM is enough

[Computeman]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

I agree this quite extreme I wish I could find a pin out if the IC AAT7212.
I see aproxamtly of these aweek. Most are Samsung warranty, Some are
TP warranty, These are the ones I get to experiment on. The next Samsung I get in that in warranty and all there is a line in pix I am going to swap that IC
To one of these rebooting panel. Just to clarify my model is a UN58TU7000FXZA Some have been shorted caps

[Davi.p]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Nooo... there's no need to torture so an lcd to find the culprit, must study first the thing and use the reasoning..
A fault state that reboots tv could happen also if the circuit do not find a dialogue with the other circuit, no components no dialogue, as i have said before very small and miniature components like mlcc can go short also only with exercise tension, so a good way to diagnose is to remove them one by one and test it after each remove..

[Computeman]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

We are trying to find out what is failing on these panels.
We know the tape trick works some of the times. We are going further this became a quest.

1 If you disconnect the LVDS cable TV will start.
2 On panels with one LVDS cable you can disconnect the the FFC cable between the two address boards it will boot.
3 To rulle out the TFT panel we cut off the ribbon cables one at time right at the glass still no boot.
4 To rule out the COB's we removed all the FFC's from the address board still no boot.

So now we are down to the something on the address board. We removed all the componets on the address board.
Still with all the componets on the address board still reboots.

Now we thinking maybe the connector is shorting removed connector from address board connected to the FFC from other address board it would boot.

To review it has to something on the address board the only thing left is them ribbon cables that are soldered on the address board. When we removed th e cables we just cut the cables from the board.

Our thoughts maybe it is the glue that is used to hold down the FFC's that go into the TFT glass has become conductive.

Has any one found asoure for the address boards

[nomoresonys]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

nice work, those flirs are very handy, another fine save.

[howardc64]

FIXED, just a shorted cap on the panel board

After finding the shorted lines to mask off, looked up the line voltages (post #69) and did some probing. The shorted lines are AVDD and VCOM.

Bought a fairly new Seek Thermal FLIR cam for $60. Injected 1.5V 1A limit on the VADD rail (low enough and no need to cut any panel COF lines for protection) and the shorted cap gradually lit up.

Removed the cap and magically both shorts went away. Put Cap from a salvaged panel board of similar size and panel fired up. Perfect.

So get yourself a FLIR cam. Mine was used 1x on Facebook marketplace for $50+tax+ship. Seek Thermal Compact for Android. About $200-$250 new. Not PRO model.

2-3 year old Samsung QLED 50" TV saved

Next time I would just go test the caps for shorted rails once fault has been determined to be on the panel side (disconnect panel cable from main board, TV boots, stable, have backlight and sound, no LCD picture)

First time I did voltage injection and FLIR short hunt. 1.5V 1A took a little for the bad cap to show. Probably could have gone higher voltage but FLIR camera makes it unnecessary anyways.

[howardc64]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Ultimately I could unmask pin 1-3, 20-46, 57-60 and have the same pic as above but no further before boot looping again.

Correction, I was able to unmask most pins except 4-5, 51-56. But same washed out ~1/2 screen picture.

[howardc64]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Got a QN50Q60TAF with same symptoms. Constantly reboots every few seconds. Quickly isolated down to the left panel board (looking at the screen from the front) as removing the flex cable between right and left panel board enables the TV to boot and play sounds. All the big caps on left panel are shorted to ground.



Google "AAT7212" marked IC on the panel board and landed here. Can add some details on OP's tape masking efforts. Appears to be same/similar panel design.

On the left panel flex connector, masking off everything except pin 1 and 46 enable the right side LCD to display (actually slightly more than 1/2 the screen) but washed out. This was noted by the OP on post #62 but I think the OP miscounted as pin 45.




But I could get no further than this removing more masked pins. I'd imagine panel/panel board can shorts out differently. Ultimately I could unmask pin 1-3, 20-46, 57-60 and have the same pic as above but no further before boot looping again.

Removing 4-5 would flicker like crazy but can make out an image.

Anyhow, I realize probably the short is in the panel itself but will do a bit more detective work (check temps on the panel flex cable, panel board, understand the board, measure some voltages, look for source of short on the board if there)

2+ year old 50" QLED Samsung TV. Looks like fairly rampant problem searching online.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

I played around with the first dead one long enough to figure out the problem area but the result was a vertical line a few pixels wide. In the end, it was trash. The last couple I've been able to feel the warm area on the shorted tab, tear it off for testing, and verify the boards work.

you know its sad how we have just accepted the fact that you cant buy a replacement panel from the manufacturer. its the weakest point of the whole tv and when it goes there aint shit you can do. frustrating.

[aaronwt6]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

tearing off ribbons eh? im guessing you had no luck with the "masking a few pins with some tape" method?

I played around with the first dead one long enough to figure out the problem area but the result was a vertical line a few pixels wide. In the end, it was trash. The last couple I've been able to feel the warm area on the shorted tab, tear it off for testing, and verify the boards work.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Just to follow up on this post. I've had three of these in the last month now with the same issue. The TVs all ran with the ribbon cable disconnected so I began tearing ribbons off the panel and every one of them had some type of short in the panel in one or more areas. Here's a pic of one of them with the ribbon removed. All were in different areas. Cheap crap of a TV.

tearing off ribbons eh? im guessing you had no luck with the "masking a few pins with some tape" method?

[aaronwt6]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Just to follow up on this post. I've had three of these in the last month now with the same issue. The TVs all ran with the ribbon cable disconnected so I began tearing ribbons off the panel and every one of them had some type of short in the panel in one or more areas. Here's a pic of one of them with the ribbon removed. All were in different areas. Cheap crap of a TV.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

i will try removing those components cause why not? oh and in other news, the other tv of this model i was talking about looking at...a 58" tho. UN58TU7000F to be exact. it also had panel problems like this one but i was able to fix it quite quickly by blocking almost all but not all of those 14 pins. i unblocked a couple of them because there were some horizontal lines and dimming but i was able to get that to go away by unblocking pins 6 and 7 if counting from the close end of the connector.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Oh NO, you didn't insult this member, who is always gracious and NEVER rude, with the BS posts of #49, #51 AND #54.

i thank you for defending my honor, good sir! i really try to give people benefit of the doubt...i hope he doesnt mean anything rude by it! so i carry on as if he didnt even if he did :P

[Davi.p]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

i have translated with google what i have written, no errors, so what you don't understand?

[nomoresonys]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Oh NO, you didn't insult this member, who is always gracious and NEVER rude, with the BS posts of #49, #51 AND #54.

[Davi.p]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

not much i have said... simply remove diodes marked from T1 to T14 off the bad board..

[nomoresonys]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

yep, I speak technical layman AND English, and I'm not a weirdo with offhand weirdo comments all the time, LIKE, HEY why no greeting or sum sad shit, like I said if you're lonely for greetings take it to twitter, this is a tv repair forum.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

sorry but i have a real hard time understanding you. thanks anyway. sorry for my long posts. but this is my style of posting on this forum. i prefer MORE details not less. especially while i am learning. i am using this space to keep track of all these details, and re reading my posts helps me to remember what i did and what i saw.

i will try to do what you said and come back with results.
once again, thank you for trying to help!