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

[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.

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.

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.

[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.

[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]

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.

[nomoresonys]

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

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

[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

[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.

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.

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

[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*

[skaktus]

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

Hello. I read the topic and thanks to it I fixed the Samsung UE50TU8002K TV. I masked the pins as shown on page 4 of this topic. The TV has been working fine for several hours now. Will such a pin masking repair work for more than a few days?

[nomoresonys]

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

Sure, it can last a very long time, maybe some members will relate how long theirs has been working.

[Braith]

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

My First BadCaps Post
I have a Samsung UA50TU8000W. It has a single ribbon cable going to the display boards.
I have achieved a reasonable fix after reading through this and several other posts and Youtube videos. Thanks Folks.

CAUTION I noted that the Mains capacitor on the power board does not appear to have a discharge resistor and was still over 250v half an hour after disconnection.

Symptoms-
1- When power connected Screen remains black. Back-light initially comes up to full brightness, dips to low level then drops out completely as set powers down. TV repeats attempt to start up about every 12 seconds.
2- Occasionally the set will begin to produce a startup chime before shutting down.
3- The LED underneath IR receiver gives one or two flashes (usually 2) at each attempt to start up. The LED flickers correctly if receiving IR signals during the several seconds before shutting down.
4- The optical I/O connector lights for several seconds each time the set tries to power up. It is an easy to see indicator of the main 12 volt rail.
5- Disconnecting the cable between power supply board and main board allows the backlight to come on at full brightness and stay on.
In this condition A13V = 12.86v which is in spec.
6- Reconnecting the cable between PS and Main I note the main power mosfet (4435MP) that provides HVIN12v is getting switched off on each power cycle however some other circuitry remains powered. (EG Winbond Flash memory etc). When HVIN12v is present the optical I/O connector lights up (as mentioned above).
7- When the single ribbon cable connecting the main board to the display board(s) (long thin boards along bottom of TV) is disconnected, the TV responds to the remote control, there is (obviously) no picture (screen black), the power remains on with the backlights lit and dipping slightly if channels are changed (hence PWM feedback to the backlight driver is working). Audio is present if there is an audio source (TV aerial etc). The Optical I/O is lit.

Procedure -
I checked all visible capacitors for low resistance on the two display boards - all ok
I disconnected the interconnect cable between the two display boards and found the TV powered up in the same condition as ‘7' above. Voltages on all visible capacitors (on the still connected board) seemed sensible.
I was in some doubt as to which ribbon cable pins to mask and extremely perplexed as to why it could possibly work.
FrugalRepair has a video called “I fixed a broken 4K 55” TV with TAPE | How to fix a TV with a blank screen” and “Repair Hack Explained | How to Fix TV Horizontal Lines - Part 2” that gives a possible explanation.
I noted that on the end of one of the Display boards were some test points marked CLR, CK1, ....CK8 which matched the FrugalRepair video.
I used a sharp (hypodermic) needle held by a springy ‘helping-hand' clamp on the test points to buzz-out the corresponding pins on the interconnect cable between the two display boards.

My reading of the situation is that there is a signal loop of some sort that detects if any of the ribbon cables have been completely disconnected.
Providing this loop is intact the main board will fire up the display boards. The display boards normally clock the screen from both sides and can signal back to the main board using CK1 thru CK8 if there is a problem or correction needed. (see Youtube video mentioned above)
Blocking these signals from one side of the display leaves the display mostly operational and allowing errors to go uncorrected. The actual operation is probably far more subtle than this, comments welcome.

I tried numerous permutations of using tiny slivers of kapton tape to block the signals on the display panel interconnect ribbon cable.
My first attempt was to block all 9 pins (7th to 15th from inner end) and I immediately got quite reasonable pictures on the screen!
A bit gobsmacked that it actually worked.
Picture showed darkening of left side of picture with lots of fine black lines. I tried various combinations of pins.
Results varied. Sometimes power cycled, sometimes patches of black lines moved around.

Incidentally, blocking the main ribbon connections appears to mess the pic up badly thus I only tried a couple of gross blocks before retreating to the interconnect cable - (comments welcome).

Best result was by blocking all interconnect CK1 to CK8 pins (8th to 15th on interconnect ribbon). Still have a few white lines at bottom of screen and a slightly weird flaring effect on slow moving images.

It would be interesting to apply this technique to the CK signals originating from the other side of the screen but this is not easily done given the single ribbon cable layout from the main board (cutting traces would be needed).

Hope this is helpful and adds to the info on this bemusing and apparently common fault.
I assume that Samsung in their wisdom have decided that the TV should become completely unusable instead of displaying a degraded picture when a display fault is detected.
I can almost see their point in that it is worse publicity if many of their products are operating poorly for years before failing completely than if the TV just suddenly fails completely and needs replacing.
Kinda nice to be able to bypass the deliberate shutdown. Thanks again folks.

[Braith]

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

My First BadCaps Post
I have a Samsung UA50TU8000W. It has a single ribbon cable going to the display boards.
...........
It would be interesting to apply this (masking) technique to the CK signals originating from the other side of the screen but this is not easily done given the single ribbon cable layout from the main board (cutting traces would be needed).

I looked at the CK1 through CK8 signals on both display boards with an oscilloscope.
All the signals on the unmasked side looked similar having a nice square 32.8vpp 17.1Khz squarewave chopped up by 50Hz 'sync or blanking' pulses. base of pulses at -6.8v, peaks at +26v.
There is a ~45degree phase change on each of the CK signals ‘sync' pulses to give a 360 degree spread as you go from CK1 to 8.

On the side I had masked off the CK1 thru 8 signals there was a messy version of that signal on 6 lines and nothing but a DC offset on 2 of them.

Trying to interpret this I masked the main board ribbon cable to see whether the main board or the display boards were originating the pulses.
The pulses disappeared completely from the display test points and the signals on the main board end went haywire and turned into 50hz ramps with a small amount of 17Khz.
I'm guessing from this that the signals are originating from the mainboard which is getting upset it doesn't have a load.
The set also rebooted twice during the time I had all 8 CK signals masked on the mainboard.

From all this I am somewhat baffled. I feel that the messy signals on the masked off side of the display are possibly leakage through the panel (Ref FrugalRepair's youtube videos mentioned in my first posting) and the two CK signals with nothing but a d.c. offset may indicate a problem on those two lines (maybe shorted caps or faulty chips not visible on the display board?).

For now, the TV is working quite well (all 8 CK signals masked off on interconnect ribbon) and further investigation will have to wait until I have time to delve deeper.
Will be interested to see how the BadCaps forum investigation evolves.
This has taken a considerable amount of time, it's been puzzling yet enjoyable. Funny old world.

[micha3]

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

I have three dead screens from UE50TU8002KXXH (BN96-52423A, replacement is BN96-55108A, panelook link https://www.panelook.com/CC500PV6D_P...iew_45683.html), one cracked post mortum. Documentation that i found at alibaba and pinout that i figured out myself












Panel 1:
-shorted VGH with VSS on detachable pcb
-when masking i've discovered heating of a glass at bottom left corner and ~1Hz slight partial pulsing in this neighborhood, masking LC1 and LC2 solved problem
-at the moment masked pins from 8 to 19 at short ribbon, visually there are some irregular horizontal black lines and some discoloration not visible from 2m and with normal content, all at left side, tv is perfectly usable

Panel 2:
-nominal voltages and resistance at VHG and VSS
-at the moment masked pins from 8 to 17 at short ribbon, visually there is more severe discoloration than in panel 1, but it's mainly brightness related, and it's not really that bad; no lines

Panel 3:
-panel shattered, allegedly rebooting even before mechanical damage
-measured short between VGH and VSS on detachable part of pcb

[D0GU]

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

I have three dead screens from UE50TU8002KXXH (BN96-52423A, replacement is BN96-55108A, panelook link https://www.panelook.com/CC500PV6D_P...iew_45683.html), one cracked post mortum. Documentation that i found at alibaba and pinout that i figured out myself












Panel 1:
-shorted VGH with VSS on detachable pcb
-when masking i've discovered heating of a glass at bottom left corner and ~1Hz slight partial pulsing in this neighborhood, masking LC1 and LC2 solved problem
-at the moment masked pins from 8 to 19 at short ribbon, visually there are some irregular horizontal black lines and some discoloration not visible from 2m and with normal content, all at left side, tv is perfectly usable

Panel 2:
-nominal voltages and resistance at VHG and VSS
-at the moment masked pins from 8 to 17 at short ribbon, visually there is more severe discoloration than in panel 1, but it's mainly brightness related, and it's not really that bad; no lines

Panel 3:
-panel shattered, allegedly rebooting even before mechanical damage
-measured short between VGH and VSS on detachable part of pcb

I've tried masking the same pins that you had on panel 2, and that seemed to fix the display issue, however just 10 seconds after startup, the image seems to corrupt and the TV powers off, I'm guessing my problem is a bit more than just the led matrix shorting.

Feels pretty bad having to repair a TV I bought new 2 months ago

[maneatingmonkey]

Thank you triplefour and others for your posts. I had the same TV with the exact same symptoms as the OP. Thanks to this thread, I was able to isolate the problem down to a shorted clock line #8 in the left side of the panel. Unfortunately without this signal the image is unwatchable, but at least I was able to confirm the integrity of the other components.

[ayubakon]

Thank you triplefour and others for your posts. I had the same TV with the exact same symptoms as the OP. Thanks to this thread, I was able to isolate the problem down to a shorted clock line #8 in the left side of the panel. Unfortunately without this signal the image is unwatchable, but at least I was able to confirm the integrity of the other components.

You have to block all CKV lines or CKV pair.