samsung un65nu6900f common problem, digging deeper

[itelite]

I just got one of these 65 inch that is, the main board is slightly different as those resistors arent present, anyone found a fix for the actual model in the post? Same reboot. Thx

Try to find the VGH pin, and work from there. It should be very similar.

[xfox]

I tried that, works as expected, tried resistance from 0-50Kohm, do you think it may need some higher resistance?

[nomoresonys]

Here's some more messing with similar problems, pretty good explanation of how the shorts can be about anywhere on those lines and results can vary widely, if you check the last comment there's a link to his continue video of it: https://www.youtube.com/watch?v=7HMGyt1nNgY

[itelite]

I tried that, works as expected, tried resistance from 0-50Kohm, do you think it may need some higher resistance?

When you say "works as expected" do you mean successful, or unsuccessful?

If successful with no color or image artifacts, I would call that a win.

Otherwise

I suppose a decent test would be no resistor at all. That would be equivalent to taping over the VGH pin (or an infinite resistor). If that works (if memory serves, you should get the boot up chime, but no image, but I could be wrong on that. then you know the problem must be on the VGH circuit, at that point I would try a very high resistance like 1Mo. then keep cutting that resistance in half until something interesting happens. Thats why I've been using a potentiometer for testing.

[xfox]

so with one of described pins disconnected power-on then 3 sec wait then connect wire, tv starts with perfect picture, was working for whole day no issues, will try 1Mo resistance yesterday, and delay switch ordered, probably would take few weeks to come. I could not find any shorts tried tape method on all pins, only those I described prevent power cycling

[itelite]

That very much sounds like this is the same problem then (if indeed we are talking about putting a wire between the VGH resistor pads or equivalent.)

Im sure you thought of this, but if not, keep your wire as is, and use it to test the various resistor values. That way you don't need to solder anything each time. I think it is just going to be a matter of finding the correct value. Start with a high value and note results. Again, as I'm sure you know, resistors in series will add, and in parallel will divide.

Couldn't hurt to verify resistance with a meter as well.

[xfox]

tried resistance from 1Mo to 0, no luck

[JGMusic74]

I am so grateful to have found this thread! Having repaired several other LCD TVs over the past several years, usually due to failed power supply capacitors, I thought I’d take a stab at this 2020 70” Samsung my neighbor put on the curb. The boot loop issue was misdiagnosed by an online tech as a bad main board. I swapped the main board and the issue remained. Fortunately I only paid $52 for it so I wasn’t out much. Thanks to this thread I was ultimately able to repair the TV by replacing the R13246 with a 15k I happened to have in my stash. I had previously isolated a single pin on one ribbon cable and the TV worked but the color saturation was degraded on the left half of the screen. With the tape removed from the pin and the resistor swapped out it is now perfect and we’ve been watching it for the last several hours with no issues. Thank you!

[JGMusic74]

I had the same results as many with the tape method. I was able to pinpoint a single pin and insulate it with tape to stop the boot loop but had major color fade on the left side of the screen. After finding this thread, I fixed the TV completely by replacing r13246 on main board 10ohm resistor with 15k with previously applied tape removed. We've been using the tv daily since Xmas and it's perfection. 🙏

[xfox]

Ok, finally got my delay switch, installed, took power 5v from USB on board, delay is set to ab 2 sec, TV is working as expected, thank you everybody for your help and ideas, maybe this one would be useful for someone else.

[ggil44]

Hi xfox, glad to see you found a work a round. I too have had no luck with changing R13246 values. The only "fix" I had was to tape pins 13 to 24 on the Right (shorter) ribbon cable which results in a color fade from Left to Right on the TV screen. Could you show a picture of what is under the blue masking tape by the ribbon cable and identify what pins or points you soldered the wires from the 2 second delay circuit from the 5V power source? Did this give you a normally working TV with no color fade? Thank you.

[nomoresonys]

Very nice work, good to see this method works sometimes when the resistor change does not, glad people are finding ways to get more use from these tvs. And SHAME on samsung for these design flaws.

[xfox]

Somehow I UI of this TV is very slow, do you guys have a same feeling?

[Cornito]

"Edited, new info at the end of the post"

Hello all,

That's a really good thing to have found this thread.
I've actually the same kind of issue With my UE58TU6905 Samsung tv.

Before moving forward with the resistor solution proposed here that seems to solve many tv.
I'd like to know if it's normal situation to do not have 25v steady on the main board when ribbon cable to drivers is unconnected?

I think that I need to get this 25v fixed before moving forward.
I get this voltage on the 22pin on my connector , when ribbon cable to driver is connected and at the beginning of the looping restart only.

Is this something that somebody already got?

Here under a picture on my main board that is a bit different of the ones shown here. I was boy able to find the resistor and nothing really clearly explained on this board

Thanks in advance for your reply.

Regards

"EDIT":
Pursuing my investigation, found one this, that the VL0 line when is isolated from the ribbon cable on the left screen side my TV stopped rebooting, only isolating this line.
But, VGH don't show any voltage output.
I've taken the resistance and found only 5.2kΩ between VGH and Ground, that seems to me a bit low.

Anybody has a feeling of i should do next?

Thanks

[itelite]

Do you get anything at all on VGH? How about with no power cord plugged in, resistance to ground on VGH, and/or diode mode measurement from VGH to ground.

Best place to start would be ruling out a sort to ground, or an open circuit.

in all my test a while ago I recall there always being some kind of measurable voltage on that VGH pin/resistor.

[Cornito]

Hello,

Thank you for the information. At one moment at had the feeling that the motherboard needed a feedback from drivers to supply the 25V.

So, resistance measurement on the motherboard from VGH to ground is 52 kOhm

VGH voltage is présent only when tv bootloops, LVDS un attached and / or bootloops stopped with tape method on LV0, no VGH at all.

Guess I need to focus of the VGH power supply DC to DC, transistors and capacitors on motherboard.

Thank you so much

[Cornito]

So back with measurements results.

No short found, DC-DC supply 1.8V, 3.3V but no high voltage.
Seems that the command from µC to activate ocilator and supply the high voltages is not there.

I've measurement resistance from VGH to Ground on Driver cards, and one is over MEGAOHM the other is 5.3kOhm, guess panel issue here compatible with trick proposed in this thread.

µC becomes hot in some seconds, My bad feeling is that the µC is short cutted, but don't know how to get proof of that.
I'm still wondering cause the TV can switch in standby mode, when requested by the remote.

I don't know if I need to give up right now...

[Cornito]

Today's Update, finally found a short to ground, attached to some caps just in the opposite side of the µC.
Some many components are in short.
I guess i need a new board, but don't know if the panel has an issue too

[nomoresonys]

Can you show a picture of the shorted components.

[Cornito]

Don't know how to ensure panel is ok, the first steps of the issue, was a small blue line on the right side of the screen, then a complete blue line to come to this end, no picture on the screen and rebooting TV.

In the red circle this is the coils that present short to GND, i can find some caps just under the

[lotas]

In the red circle this is the coils that present short to GND, i can find some caps just under the

There is one choke and should be on the ground, since a negative voltage (-) relative to the ground is generated on this line (VOFF = VGL = VGOFF = VEEG).

[Cornito]

Ah that's a good information, i was not aware of.
But as I've got some caps short-cutted I need to know which one is faulty.

I'll take picture of the caps found in short, maybe the short is in the micro controller

Thank you for your support

[Cornito]

There are the pictures of my motherboard.

On the motherboard I've marked the short with a black pen.
I've a doubt on a component that looks like a transistor but I'm not sure.
I can read values between all pins. 🤔
but no short as measured on caps close to 0.2ohm.

Thank you in advance.

Damien