Samsung UN70NU6900FXZA PSU failure? - Badcaps

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ratdude747

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#1

Samsung UN70NU6900FXZA PSU failure?

08-26-2021, 08:40 PM

Scored a Samsung UN70NU6900FXZA curbside several days ago.

Issue is it won't turn on and blinks the power light (red) constantly. Upon opening it up and retesting, it is flashing the backlights (they seem to be good).

The marked standby power is reading 12.9VDC, it's supposed to be 11.5VDC. Power on is reading 0.3VDC. See attched pictures for what I'm referring to (referenced to the 0V pin on the main board cable connector). This a start? Or am I barking up the wrong tree (bad main board, etc.)?
Attached Files

Last edited by ratdude747; 08-26-2021, 08:41 PM. Reason: Pics didn't upload... my bad!

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Storyteller12

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#2

08-27-2021, 05:51 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Most of the nu series TVs have bad backlights.
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RDC55

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#3

08-27-2021, 10:29 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by Storyteller12

Most of the nu series TVs have bad backlights.

And I guess many of that series also have internal damage from the LED burn.

https://www.badcaps.net/forum/showthread.php?t=96567

With Samsung models you should be able to test the Power Supply / Backlights by disconnecting the interconnect cable between the Main board and Power Supply. The backlights should come on when power is applied if the Power Supply and LED's are operational.
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ratdude747

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#4

08-27-2021, 11:25 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by RDC55

And I guess many of that series also have internal damage from the LED burn.

https://www.badcaps.net/forum/showthread.php?t=96567

With Samsung models you should be able to test the Power Supply / Backlights by disconnecting the interconnect cable between the Main board and Power Supply. The backlights should come on when power is applied if the Power Supply and LED's are operational.

Will try when I get home from work. The back lights were coming on at times during the blinking red light routine... white and bright.

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ratdude747

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#5

08-27-2021, 05:31 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Unplugged the main board cable from the PSU, plugged in power, backlights came on and stayed on. Nice and bright.

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CapLeaker

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#6

08-27-2021, 06:37 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Can you post pics of all the boards? And what is your power on now?

Last edited by CapLeaker; 08-27-2021, 06:40 PM.
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ratdude747

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#7

08-28-2021, 06:36 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by CapLeaker

Can you post pics of all the boards? And what is your power on now?

Attached are pics.

Cable unplugged, power on is at 0v. Still 12.95v on standby.
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RJARRRPCGP

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#8

08-28-2021, 08:26 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Very sad! Looks like it was made in 2019!

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RDC55

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#9

08-28-2021, 01:37 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by ratdude747

Attached are pics.

Cable unplugged, power on is at 0v. Still 12.95v on standby.

Seems a bit odd. So the 12.95V is from the JP822 jumper to chassis ground? You stated earlier referenced to the 0V pin on main connector, which I suppose could be chassis ground but that needs to be verified. Also, if the cable is unplugged you can't be using that point of reference in this second measurement.

Power On 0V? With Samsung I believe all the commands should float high when the Main is disconnected. So just to be sure that Power On you are measuring is pin 8 on CNM0801 to chassis ground?
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CapLeaker

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#10

08-28-2021, 02:14 PM

Re: Samsung UN70NU6900FXZA PSU failure?

What are the voltages on each pin on cnm801? Sounds almost like the main board has a problem turning the whole tv on… probably there is a voltage missing on one of the pins on cnm801.
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ratdude747

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#11

08-28-2021, 10:18 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Verified that the 0V pin I was using is indeed tied to chassis ground.

Odd thing is the power on PSU connection (the jumper link pictured in the first post) is showing up as shorted to ground... both polarities, so not just a diode. Something on the PSU board shorted out???

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CapLeaker

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#12

08-29-2021, 05:12 AM

Re: Samsung UN70NU6900FXZA PSU failure?

disconnect the main board and force the PSU on. Then you can see what's going there.
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R_J

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#13

08-29-2021, 05:55 PM

Re: Samsung UN70NU6900FXZA PSU failure?

In post #5 you proved the power supply is working, Pin#8 of CNM801 is power_on. it is connected to RM870 which should be the pullup resistor for the standby transistor(QM854?).
Check the voltage on JP819, this is the power_on line going to the base of the standby transistor and should be around 12v when the power supply is on.

Last edited by R_J; 08-29-2021, 06:03 PM.
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ratdude747

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#14

08-30-2021, 08:12 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by R_J

In post #5 you proved the power supply is working, Pin#8 of CNM801 is power_on. it is connected to RM870 which should be the pullup resistor for the standby transistor(QM854?).
Check the voltage on JP819, this is the power_on line going to the base of the standby transistor and should be around 12v when the power supply is on.

All tests since post #5 have had the main board cable unplugged from the the PSU.

If power_on is pulled up, then why with no cable connected is it reading 0v and coming up as a dead short to ground in both directions? Assuming this standby transistor is on the PSU, that makes me think it blew up and shorted out?

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RJARRRPCGP

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#15

08-31-2021, 01:22 AM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by RJARRRPCGP

Very sad! Looks like it was made in 2019!

At least 2019, if not the 2020s!

ASRock B550 PG Velocita

Ryzen 9 "Vermeer" 5900X

32 GB G.Skill RipJaws V F4-3200C16D-32GVR

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"¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

"There's nothing more unattractive than a chick smoking a cigarette" -Topcat

"Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

"did I see a chair fly? I think I did! Time for popcorn!" -ratdude747
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R_J

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#16

08-31-2021, 05:02 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by ratdude747

All tests since post #5 have had the main board cable unplugged from the the PSU.

If power_on is pulled up, then why with no cable connected is it reading 0v and coming up as a dead short to ground in both directions? Assuming this standby transistor is on the PSU, that makes me think it blew up and shorted out?

Is this the BN44-01016A board? If it is, is the jumper JP819 shorted to ground?
Pin#8 of CNM801, connects to two resistors, RM870, which is the pullup res. and its other end connects directly to the stb:11.5v AND RM871 which connects to JP819 and then to QM854

Last edited by R_J; 08-31-2021, 05:16 PM.
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ratdude747

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#17

08-31-2021, 07:46 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by R_J

Is this the BN44-01016A board? If it is, is the jumper JP819 shorted to ground?
Pin#8 of CNM801, connects to two resistors, RM870, which is the pullup res. and its other end connects directly to the stb:11.5v AND RM871 which connects to JP819 and then to QM854

That's the board number.

Pulled the board. Seems I was probing the wrong thing as power on (JP811).

JP819 is not shorted to ground. your description matches. After re-installing the board, JP819 is reading 4V when the mainboard cable is unplugged. Plugging the cable in (and re-applying power) puts JP819 at 3V, but it's occasionally spiking out of meter range (which corresponds with the mainboard "resetting".

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RJARRRPCGP

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#18

10-05-2021, 04:34 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Originally posted by RJARRRPCGP

Very sad! Looks like it was made in 2019!

Looks like 2019 or 2020! It wouldn't surprise me if the panel was made in 2019, but regardless, this is way too premature!

ASRock B550 PG Velocita

Ryzen 9 "Vermeer" 5900X

32 GB G.Skill RipJaws V F4-3200C16D-32GVR

Arc A770 16 GB

eVGA Supernova G3 750W

Western Digital Black SN850 1TB NVMe SSD

Alienware AW3423DWF OLED

"¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

"There's nothing more unattractive than a chick smoking a cigarette" -Topcat

"Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

"did I see a chair fly? I think I did! Time for popcorn!" -ratdude747
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MikePCS

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#19

04-28-2022, 04:55 PM

Re: Samsung UN70NU6900FXZA PSU failure?

Hello -

Sorry to bump an old thread, but I have this same exact TV with identical symptoms and voltage readings

my STB is 13V

and my On voltage is in the 4's - same as you

did you ever find a resolution to the issue?

I bought this TV only 14 months ago, out of warranty and trying to salvage!

Thanks
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