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

[x_orange90_x]

I looked yesterday for my spare and I guess during a bout of cleaning I threw it away, without removing the boards from it 😔. I have a similar one but it's a TU7000 and they have completely different main boards. I will still play around with the ribbons and such to see if I can make something change. I keep the parts and ribbons from almost all of the junk ones I toss. Maybe I'll get lucky and only need a new ribbon. 🤷🏼

Upon closer inspection I see it has faint lines on the right half of the screen. I played with the ribbons and cleaned then but it made no difference. I pulled the boards out and I'm gonna toss the rest

[x_orange90_x]

I looked yesterday for my spare and I guess during a bout of cleaning I threw it away, without removing the boards from it 😔. I have a similar one but it's a TU7000 and they have completely different main boards. I will still play around with the ribbons and such to see if I can make something change. I keep the parts and ribbons from almost all of the junk ones I toss. Maybe I'll get lucky and only need a new ribbon. 🤷🏼

[x_orange90_x]

Notice how the bottom isn't protected, so just do the sides and top with the tool, don't stick it thru the bottom part of tv, the bottom will pop off once the rest is done: https://www.youtube.com/watch?v=kGxnt9Lhy7s

Thank you! I will do this. It never goes as smoothly as in those repair videos tho. I think they've opened up the TV's a couple times BEFORE making the video so they don't embarrass themselves struggling for 20 minutes 😂

[nomoresonys]

Notice how the bottom isn't protected, so just do the sides and top with the tool, don't stick it thru the bottom part of tv, the bottom will pop off once the rest is done: https://www.youtube.com/watch?v=kGxnt9Lhy7s

[x_orange90_x]

Update: FIXED

After two days of attempts and many headaches i managed to get the tv running with (almost) no problems at all.
No taping solution worked for me, even though I tried different tape positions and lenght on both the main and the intercom ribbon cable.
After I simply swapped the two ends of the main ribbon cable (the one from mb to panel boards) the tv started. I then tried to put the cable back in the correct order and it worked as well.
My explanation is that, after some time, the heat coming from the chassis damages the bend in the middle of the ribbon cable. In fact, in order to put it backwards I had to use a hairdryer to soften the glue on the bend and straighten.
Otherwise no other explanation seems possible to me.
The only problem is that tiny dark horizontal lines appeared in the upper half of the screen, and they fade from right to the left (which makes me think this is not a panel damage but a problem with the tcon). In addition some of those lines are permanent, others appear and disappear every few seconds, alternating. Also, those lines change color depending on the background (way more noticeable when the background is reddish).
Hope this can help.

I just picked up a UN50TU8000FXZA yesterday that is doing this exact same thing. Turns on and goes to the Home Screen then reboots after about 10 seconds. Mine however responds very slowly. I tried to get to the settings menu and it freezes for a couple seconds before it moves within menus or even changes the selection. I also noticed right before it was about to reboot it dimmed and had distorted colors and faint horizontal bars. When its on the image is perfect. I am led to believe it's a main board issue from what I seen. I believe I have another one of this model with a cracked screen, and if so I'll definitely do some part swapping to see what happens. Given the inconsistency regarding successful "tape fixes" that people are reporting, I don't think there's nearly as many "bad panels" as believed.

What is the proper way to disassemble these? There's no screws and I've seen this before but I cracked one trying to open it and another was already cracked and I just ripped it open to get the parts out. Sometimes there's weird metal bars running through the frame on these tvs. Is that the case here?

[nomoresonys]

The ends may just be dirty, try cleaning them with a pencil eraser or isopropyl alc.

[federuo32]

Update: FIXED

After two days of attempts and many headaches i managed to get the tv running with (almost) no problems at all.
No taping solution worked for me, even though I tried different tape positions and lenght on both the main and the intercom ribbon cable.
After I simply swapped the two ends of the main ribbon cable (the one from mb to panel boards) the tv started. I then tried to put the cable back in the correct order and it worked as well.
My explanation is that, after some time, the heat coming from the chassis damages the bend in the middle of the ribbon cable. In fact, in order to put it backwards I had to use a hairdryer to soften the glue on the bend and straighten.
Otherwise no other explanation seems possible to me.
The only problem is that tiny dark horizontal lines appeared in the upper half of the screen, and they fade from right to the left (which makes me think this is not a panel damage but a problem with the tcon). In addition some of those lines are permanent, others appear and disappear every few seconds, alternating. Also, those lines change color depending on the background (way more noticeable when the background is reddish).
Hope this can help.

[nomoresonys]

I have the same problem,with UA50BU8000W, but i noticed something different?
When I unplug the ribbon between the two LCD boards, it stops cycling, and does not show a picture like everyone else.
But when i plug the ribbon back while the TV is still on!, The TV works normaly every time? with perfect picture and no tape on ribbon needed,
Its not a fix, when i turn the TV off i have to repeat, but i can see the TV functions normaly if you bypass the booting process?..

Seems like they may have been having similar issues in this thread, solved by using a larger ohm resistor, check it out: https://www.badcaps.net/forum/troubl...digging-deeper

[federuo32]

Hello, I have a very similar problem with this tv: UE50TU8070U(XZT).
As you described, the tv continued to reboot about every ten seconds. I opened the back and disconnected the ribbon cable between the two panel boards and the tv started.
I could hear the starting melody but no picture on screen, which was backlit but black, like the panel remains undriven. The tv responds to IR inputs.
After some time i managed to understand that the cause of the rebooting was a short circuit between pin 1 and pin 46 of the mentioned ribbon cable caused by an internal short circuit between the pins on the second panel board (left side from the front of the screen). I used a thin piece of tape to cover one of the two pins but the tv still shows no picture. None of the main voltage rails of the panel boards can be detected, just few random voltages like 1.8v, 0.11v and ecc like OP already detected. If I let the tv in the reboot state, instead, those voltages can be measured for a short period of time (as already reported).
Also cannot find the AVDD line to verify a possible short circuit between AVDD and VCOM as described in post n.86
Taping the clock lines does not help since I didn't manage to get picture.
Do you have any other possible solution? It would be a shame to throw away the tv

[kostas22]

I have the same problem,with UA50BU8000W, but i noticed something different?
When I unplug the ribbon between the two LCD boards, it stops cycling, and does not show a picture like everyone else.
But when i plug the ribbon back while the TV is still on!, The TV works normaly every time? with perfect picture and no tape on ribbon needed,
Its not a fix, when i turn the TV off i have to repeat, but i can see the TV functions normaly if you bypass the booting process?..

[nomoresonys]

Rubbing a candle on those components is another little thing you can do to try and isolate a heat related issue. See where the wax melts first.

[samsug]

Hey there, I happen to have the about same symptoms. Plug in the TV, it starts, shows me a very crisp picture for about 20s, then first goes black with lit backlight and then reboots and with each reboot the on time decreases rapidly. Unplug it for 10s and rins and repeat.
When I unplug the ribbon between the two LCD boards, it stops cycling, but does not show a picture.
I glued of everything besides pin 1 and 46 as somebody noted. This caused the TV to only show a picture one third of the screen and quite a bit more distorted than usually, and still shuts down after a few seconds. Maybe even a few seconds later.
I glued up only the clock pins, and it showed a distorted image and shut down anyway.
The voltages over the caps on the second board seem to be “normal” at about 15.6-7 V.
Since I don't have a FLIR, I can only use my lips to find warmer components on the board. The only component I found with this so far is the AAT7212, but since it appears to be a voltage regulator, this seems to be ok to me.

Is there any hope for me / any other trick / measurement left or am I just cooked

Thanks so much in advance, and I just want to say how incredible your work here in this thread is!

[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.

[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.

[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

[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

[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.

[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.

[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.

[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?