UN70NU6900FXZA power cycle, no picture - workaround found

[MikePCS]

Hello,

I have a just of warranty 70" Samsung 6-series that out of the blue stopped getting a picture, but I had sound. During the initial outage, the picture came back momentarily and then faded out. The next morning the TV worked on a quick test, but trying it again later it didn't.

When I have the mainboard disconnected from the power supply, the TV powers on with full LED brightness and stays on

When I plug the mainboard in, the LEDs go bright-->dim--off -->repeat, while the red status indicator blinks 2x

WORKAROUND: Unplug one ribbon cable from mainboard to panel - (doesnt matter which) - turn on TV, and reconnect ribbon while TV is on - I get a normal looking display.

Sometimes I can turn the TV off/on - even disconnect cord from outlet - and the TV still works! Other times it doesn't and I have to repeat the process.

This person seemed to have an identical problem (even the same voltage readings) but there was never an outcome posted

https://www.badcaps.net/forum/showthread.php?t=98468

I know these units have panel issues, but based on my experiments Im still not sure if its a mainboard causing this.

Any help would be appreciated if this unit can be salvaged!

[dskall]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

I would try running a wire from 12v up to t-con. Or monitor the voltage. They maybe marginal on their conductors on power lines to panel.

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

If you still have this tv it is a good candidate to test the method here.
Can you measure voltage on both sides of R13246 on the main board, and ground? If it measures significantly below 25VDC your fix is likely in the thread below.

https://www.badcaps.net/forum/showthread.php?t=107445

[MikePCS]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

If you still have this tv it is a good candidate to test the method here.
Can you measure voltage on both sides of R13246 on the main board, and ground? If it measures significantly below 25VDC your fix is likely in the thread below.

https://www.badcaps.net/forum/showthread.php?t=107445

I do have the TV still, Ive been leaving it powered on, and it has been fine.

I hung it back on the wall with the rear cover off, so if it accidently turns off I just disconnect the ribbon and plug it back in.

I have gotten pretty good at this, where I don't even have to look behind the TV anymore. I can do it all by feel

However I would love a permanent fix. I will do some testing and report back.

[nomoresonys]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

those ribbon cables won't last too long at that rate, too delicate.

[Lupin3]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

I too have been dealing with this issue. I have a complete picture when one of the ribbons is connected and then I turn the tv on and then carefully connect the second ribbon and voila.

I found that if both ribbons are connected and I tape the 2nd pin of the longer ribbon (or is it the 2nd last pin counting down from the top), the tv does not go into the 2-blink shut-down anymore but I have no picture just sound in the on position.

I believe this is the STV pin I'm covering but do not know its need???

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

Sounds good feel free to post a board picture if you are unsure of the resistor in question, i can mark it for you. a 12K worked for me, but i tested as high as 150k, so anywhere in between is probably fine.

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

I too have been dealing with this issue. I have a complete picture when one of the ribbons is connected and then I turn the tv on and then carefully connect the second ribbon and voila.

I found that if both ribbons are connected and I tape the 2nd pin of the longer ribbon (or is it the 2nd last pin counting down from the top), the tv does not go into the 2-blink shut-down anymore but I have no picture just sound in the on position.

I believe this is the STV pin I'm covering but do not know its need???

There is a pinout listed in the other thread if you want to reference that for what pin you are blocking.

In my testing the only pin that really mattered was pin 84. The clock lines next to it could also be blocked with no change, but if 84 was blocked it booted fine but with a noticibley degraded image on half the screen.

[Lupin3]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

I measured the voltage of the R13246 and found that when the ribbon is plugged in (after connecting it with the tv already on) it measures 25V on the north side but the south (other side) = 0V.

With the ribbon unplugged, it measures 0V for both sides.

Using chart, measured Pin 95 (FB_TRDY_3) = 0.003V

What is FB_TRDY_3 ?

[MikePCS]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

itelite,

I really appreciate you bumping this thread to let me know your success.

Ive read the other thread. No expert at this, but I think I followed along

The final fix on this is just to replace the R13246 resistor with a 10k value?

Mind posting a link to replacement on Mouser or DigiKey?

Thanks!

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

I measured the voltage of the R13246 and found that when the ribbon is plugged in (after connecting it with the tv already on) it measures 25V on the north side but the south (other side) = 0V.

With the ribbon unplugged, it measures 0V for both sides.

Using chart, measured Pin 95 (FB_TRDY_3) = 0.003V

What is FB_TRDY_3 ?

interesting. It really should be 25v when the top ribbon cable is unplugged. At least it was for my measurements and fix. With the cable unplugged that resistor should be 25v going into a 10ohm resistor (will remain 25v), then going no where at all (open). Just to be clear, for your measurement you are putting black probe on a ground point, and red probe on either side of the resistor, correct?

Also can you verify that your resistor actually measures at 10ohm? Your measurements seem impossible if it is indeed 10ohms.

If you dont mind, can you repeat the test with the tv unplugged, top ribbon cable unplugged, plug in power cord (no need to press power button), black probe on ground (metal case of screen), red probe on one side of resistor (note result), move red probe to other side of resistor (note result).

Then if you can unplug power again and do the same procedure, with the ribbon cable plugged in.

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

itelite,

I really appreciate you bumping this thread to let me know your success.

Ive read the other thread. No expert at this, but I think I followed along

The final fix on this is just to replace the R13246 resistor with a 10k value?

Mind posting a link to replacement on Mouser or DigiKey?

Thanks!

It is an educated speculation at this point. My success involved running a wire and resistor to bypass the ribbon cable, but in theory the same can be accomplished by replacing that resistor (currently a 10ohm) with a 10k.

Any resistor at all will do, it passes close to no current at all. no harm in pulling one off another electronic device/donor board.

[Lupin3]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

interesting. It really should be 25v when the top ribbon cable is unplugged. At least it was for my measurements and fix. With the cable unplugged that resistor should be 25v going into a 10ohm resistor (will remain 25v), then going no where at all (open). Just to be clear, for your measurement you are putting black probe on a ground point, and red probe on either side of the resistor, correct?

Also can you verify that your resistor actually measures at 10ohm? Your measurements seem impossible if it is indeed 10ohms.

If you dont mind, can you repeat the test with the tv unplugged, top ribbon cable unplugged, plug in power cord (no need to press power button), black probe on ground (metal case of screen), red probe on one side of resistor (note result), move red probe to other side of resistor (note result).

Then if you can unplug power again and do the same procedure, with the ribbon cable plugged in.

Thankful you're looking into this...

Following your exact procedure: with the ribbon unplugged but tv on (backlights are on), top and bottom readings are 0.117V. With tv on standby, readings = 0V. With plugging in ribbon after turning on = 25.4V.

Resistor measures 10.3 ohms on standby, 10.3 ohms with backlights on, 18 ohms when top ribbon plugged in and after being on with red probe on top (North) side and black probe on bottom (South) side but 2.6 ohms with probes reversed.

[itelite]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

Interesting. That is not consistent with my prior work. There is no harm in trying a 10K in that resistor spot, but it is a SMD so if you are not comfortable working on the board dont bother.

For future reference, you will typically never want to use resistance mode measurements on a live/active/powered circuit. Best case your reading will be inaccurate, worst case you will blow up your meter and/or damage the device under test. That said, it sounds like your resistor is measuring within spec (as it was on mine).

[Lupin3]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

Thanks again for the feedback - especially the safety tips

I won't be soldering either since I'm not really that steady or confident with this procedure.

With these measurements, or trying something else that involves a simple test, is there a way to tell if my issue lies with a problem in the Mainboard or within the LCD drivers? If the former, than I could try another purchased board but they really are hard to come by or expensive...

[joelshort987654321]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

still working in 2023

[ggil44]

Re: UN70NU6900FXZA power cycle, no picture - workaround found

Sorry to revive an old thread but I have a UN70NU6900FXZA and have read through the threads and tried the “fix” without any success. Same symptoms 2 blinks, unplug TV, disconnect ribbon cable, plug in TV and power up, wait for greeting tone then plug in ribbon cable and I get a perfect picture and sound. So, I desoldered the 10-ohm resistor and replaced it with a 15K, then 35K, then 55K, then 98K, also tried connecting them to test point on the buffer board with a wire as shown and nothing cured the problem. With those other resistors I can still do the start without ribbon cable and then plug in ribbon cable and get a normal picture. I don’t get a greeting tone with any of the other resistors replacing the 10-ohm resistor but I didn’t get one with the 10-ohm either. I am not sure where to go from here. Any ideas? Is there a way the shorted components on the buffer board can be identified?

[ggil44]

Update, Through trial and error I found that covering pins 13 – 24 on the R ribbon cable got me the best results. I can turn off and on the TV with the remote and get a picture and sound without boot loop. Unfortunately, I get the dreaded color fade from left to right in the picture now. I haven't seen any resistors on the main-board that look like good candidates to change R values with. Masking the Right Ribbon cable is the only way I have been able to bring it back to “normal”. Masking the Left Ribbon cable didn't work for me.

[rjanders]

Trying to fix my brothers UN70NU6900FXZA YA02 with the same issues. Tried swapping the mainboard, no luck. I get the startup sound with old board, or replacement board, but have never been successful getting the picture back after re-connecting the ribbon cables. About to dive into the wire jumper trick and/or replacing the resistor. I wonder if my replacement board is not "new". Maybe has the same issue as the original.... Seems like one of them would work unless the problem lies elsewhere.

[EazyBone]

Trying to fix my brothers UN70NU6900FXZA YA02 with the same issues. Tried swapping the mainboard, no luck. I get the startup sound with old board, or replacement board, but have never been successful getting the picture back after re-connecting the ribbon cables. About to dive into the wire jumper trick and/or replacing the resistor. I wonder if my replacement board is not "new". Maybe has the same issue as the original.... Seems like one of them would work unless the problem lies elsewhere.

The problem doesn't involve your main board, the problem is the panel. Altering the main board is a potential "fix" for the problem. Look for the other thread on main page talking about un65nu6900 as it's actually talking about this exact model and the title was a mistake.

Don't buy another main board because that's not the problem. secondly if you can solder try doing what is in that thread. Read the whole thing

[ggil44]

Thanks, itelite for your posts on how you brought the UN70NU6900F back to life. I unfortunately had no luck with your methods even though the remove and replace the ribbon cable during starting did work for me. I posted my efforts in the Nov 20 post in this thread using various resistors. I read somewhere that the R ribbon cable was a mirror of the L ribbon cable so I went back to trying to mask the R ribbon cable and finally got some success. Through trial and error I found that covering pins 13 – 24 on the R ribbon cable got me the best results. I can turn off and on the TV with the remote and get a picture and sound without boot loop. Unfortunately, I get the dreaded color fade from left to right in the picture now. I haven't seen any resistors on the main-board that look like good candidates to change R values with. Masking the Right Ribbon cable is the only way I have been able to bring it back to “normal”. Masking the Left Ribbon cable didn't work. If you have any ideas how I could eliminate the Color Fade from left to right on the picture, I would greatly appreciate it. I have enclosed a couple of pictures of my “progress”. Thanks again and Happy New Year to everyone.