Trying To Fix: Samsung UN50TU7000 - Weird Fading Screen then Red blinking light

[lotas]

Setting TV into Factory Mode

[KYBOSH]

Setting TV into Factory Mode

Thanks for this. This is the (most common) code that I came across as well but I wanted to ask before I started.

[KYBOSH]

Ok, but you did not tell wich board you've changed, the main board? Can you remove the heatsink shield and place a good very bright photo of it? (preferably near 2000x2000), i see the tcon circuitry is integrated with that and needs voltage injecting, so a bench psu is suitable..
but in case you have changed it maybe the fault is in screen's strip boards, especially tiny caps, so you need to locate wich pins connects the 15-17v rail to the panel, and inject some voltage gradually to these until the bad cap turns hot and locate it.. i will tell you how larer..


this is a difficult task, the other alternative maybe easier, is to use the tv long enough until the working state shortens until the bad cap turns completely shorted and you can easily locate it with multimeter.. bye

I took my FLIR camera and watched the panel circuit boards as the TV turned on and eventually blanked out.
Couldnt see anything out of the ordinary (no specific SMD getting hotter than the others). For the most part the board stayed cool but the COFs were the ones getting hot.
This was across the board not no one seemed to get hotter than the other. The display went dead after a minute or so but I will try to enter the Service Menu and see if I can quickly get to the Factory Reset section before it dies.
Before I do this though i will take my multi meter and go around the panel circuit boards to see if I can find a shorted capacitor(s). At least I will be able to check that off the list.

Also the Wifi card (located with the power button) was getting hot but maybe this is normal operating temperature.
I did not have a chance to see if the wifi actually worked as I have such a short time before the display dies.

[Davi.p]

You can't locate a bad cap with set unplugged i think, because if any short, it reveals at tv powered on, in this case, but if cof are very very hot them can also be the problem unfortunately, try eventually to keep them cool with freezer spray until the set stays on more than the minute.. check with lupe if some cof are not sealed well around.. also the MB SoC is a possible culprit, bad solder balls, maybe on the die, sometimes Samsung Soc have 2 die on it, try to cooling test also on it..

[KYBOSH]

...You can't locate a bad cap with set unplugged i think, because if any short, it reveals at tv powered on....

I was unaware of this! Is this for partially failing caps (only shorting when under load)?

[Davi.p]

yes..

[Davi.p]

If you have a ice spray can you can spray it under the processor , or even on top if nothing happens under, in the moment the fault begins.. see if the image returns..
you can even do the same test on the PMIC for the tcon section of MB, i need the BN41 code of it to find a good photo and i point it..

[KYBOSH]

If you have a ice spray can you can spray it under the processor , or even on top if nothing happens under, in the moment the fault begins.. see if the image returns..
you can even do the same test on the PMIC for the tcon section of MB, i need the BN41 code of it to find a good photo and i point it..

Thanks for the assist davi
The part number is BN96-51849F.
I could put some thermal pads on the bottom of the board to see if that keeps the chips cooler longer. I tried applying an icepack to the heatsink but it didnt help at all.

[Davi.p]

Ok the PMIC is the square one to the right of the heatsink (VPMS3RT?)

the correct replacement board is bought by BN96 code..

[EazyBone]

I'm not sure if that test is valid, but if no freeze spray you can take a can of air duster and flip it upside down and hit it (don't shake first) and this will freeze it. Then turn it upright and run some air on it and it'll freeze more.

[Diah]

it seem you still didn't inter service menu and called hard reset ?!

[Davi.p]

The appearance of the board and the model code let me think is a very recent tv, more probably there is a short circuit matter

[lotas]

No, not new, almost 4 years old.

[Davi.p]

I said recent, 2021 is recent, and very good shape, no bga / qfn soldering problem for me..

[KYBOSH]

Sorry for the delay in getting back to this one guys. Had other things on my worktop I wanted to get sorted out.
Diah I have not had the chance to try the reset bcos the TV never stays on long enough for me to get far into the menus.
Otherwise this was the first thing I was hoping to try that might work.
lotas EazyBone here's an interesting phenom which lends weight to Davi.p 's idea of a short.
While burgers were on the grill I started probing the panel boards as the display was restarting.
As the display came on the capacitors would read as shorted... and when the display cut out the short would go away!
I giggled at delight as I watched this happen.
The caps highlighted in hot pink are the ones which would short on and off as the display cycled on and off.
The one in red is the only one that read a constant resistance no matter what the state of the display was.



The cycling was due to the power supply cutting on and off. I could hear the faint clicking sound coming from it.
The COF was getting noticeably hot as the cycles continued. After a while of probing likely accidentally shorting adjacent caps with my leads the display stayed on for a long time.
I eventually unplugged the TV as i didnt want to burn anything out.

Most of the caps on this panel board did not exhibit a short as the display can on and off. Only the caps in this region of the display board. This is the farthest left-hand (facing the back of the TV).
I dont know what the rating of that cap is otherwise I would replace it. It may also have something to do with IC10 but I will leave that until after I have tried the simple things first.
My plan now is to look at the other parts of these panel boards to see if IC10 has a sister chip and if it does i will get the rating of the corresponding cap from it.

[Davi.p]

wait.. you can't test live circuits with ohm meter, usually it makes connection between the two points, the only test you can do is in volts, if those marks 0 then probably there is a short, but image present means no shorts at the moment.. remember my advice, maybe not the best one, that if you keep the tv running itself with a source in, it will probably turns completely shorted so you can.probe it better, but we are not sure the panel is the fault

[KYBOSH]

wait.. you can't test live circuits with ohm meter, usually it makes connection between the two points, the only test you can do is in volts, if those marks 0 then probably there is a short, but image present means no shorts at the moment.. remember my advice, maybe not the best one, that if you keep the tv running itself with a source in, it will probably turns completely shorted so you can.probe it better, but we are not sure the panel is the fault

Now i feel really silly!
How did i not realize that you could not measure resistance on a live circuit??
Wonder if Ive ever done this before... unlikely.

Thank you for pointing this out.
I will grab an Amazon fire stick and let it play a movie while I try to figure this thing out.

[Davi.p]

the freezing spray is maybe the fastest test you can make

[KYBOSH]

I got some canned air today prepared to do the test. I plugged the TV to mains and waited for it to cutoff but it never did. But while i was waiting i figured i might have enough time to do a hard reset so i grabbed the remote and did just that (i think). There were 3 options under thr reset menu and one was grayed out. I choose SVC RESET as it seemed most appropriate. The TV is running now on an extended testing in the garage. Only thing i did out of the ordinary was disconnect the small flex film cable which connects the left panel board to the right and turned the TV on tomsee what would happen. Nothing happened. The TV's backlight came on (and stayed in) and there was no image on the display.

After the TV reset i noticed some slight artifacts in the form of black lines (running horizontally and only on the left side) coming in and out near the side of the display. So faint and fleeting i couldnt catch it in a picture. This might me there is a short or the begining of a short in this panel. I will be back in about 6 hrs and we'll see if the TV is still running.

[Davi.p]

Yes there is a non repairable short within the glass matrix, more than this there could be also some bad caps where you measured last time.. but the heating CPU could be another problem again..