Samsung UN50NU6950FXZA ( All In One )

[TVAddict]

As the title states, this is one of those all in one boards, set is non responsive, not turning on, no red standby light, yet there is 3.3v present also has 11.8v present as seen in pictures, nothing seems blown, tried disconnecting panel ribbons and backlight connector, same result, any suggestions or help is greatly appreciated..Cheers.

[TVAddict]

Re: Samsung UN50NU6950FXZA ( All In One )

Forgot to mention, no backlight voltage...

[CapLeaker]

Re: Samsung UN50NU6950FXZA ( All In One )

Disconnect the main board from the PSU, then plug the TV in. The backlights should turn on and all power rails should be present. If that’s the case, I’d be pointing at the main board.

[lotas]

Re: Samsung UN50NU6950FXZA ( All In One )

Disconnect the main board from the PSU, then plug the TV in. The backlights should turn on and all power rails should be present. If that's the case, I'd be pointing at the main board.

On this chassis, it is not possible to disconnect the power supply from the motherboard.

[TVAddict]

Re: Samsung UN50NU6950FXZA ( All In One )

On this chassis, it is not possible to disconnect the power supply from the motherboard.

LOL, quite right, i don't feel anything getting hot to suggest something is shorting, the CPU is cold, i hear a faint whining noise in and around the middle part of the board.

Thanks for your replies guys..

[CapLeaker]

Re: Samsung UN50NU6950FXZA ( All In One )

You did check the fuse and if power is present on the main filter capacitor? If the fuse is blown and you figured out there is a short, I’d be removing the glue on the mosfet above the main filter cap under that heat sink and see if it is shorted. I also see a bunch of little test points also one with “key input to” and “led stby on” etc. I think you gotta poke around on it and see what you got.

[TVAddict]

Re: Samsung UN50NU6950FXZA ( All In One )

You did check the fuse and if power is present on the main filter capacitor? If the fuse is blown and you figured out there is a short, I'd be removing the glue on the mosfet above the main filter cap under that heat sink and see if it is shorted. I also see a bunch of little test points also one with “key input to” and “led stby on” etc. I think you gotta poke around on it and see what you got.

First thing i checked was the fuse, i do have power at the main cap and mosfet is not shorted, as i mentioned above in my first post i do have stby voltages 3.3 and 11.8v.

I'll keep on trying, take a closer look at those marked voltage test points,maybe something will turn up..

[CapLeaker]

Re: Samsung UN50NU6950FXZA ( All In One )

Remove the shield for the main processor, maybe you can find the data sheet for the main processor and see if it gets any Stby voltage at all. You also can try to heat or freeze it with a can of air upside down.

[R_J]

Re: Samsung UN50NU6950FXZA ( All In One )

Check if you have any voltage to the backlights, monitor the voltage across LED- and LED+ If there is voltage what is the value? it should be around 120vdc
If there is no voltage at those points, check the voltage across Discharge(+) and Discharge (-) (the points near the backlight plug)

[TVAddict]

Re: Samsung UN50NU6950FXZA ( All In One )

0v at backlight testpoints, thanks for your response R_J

Will try your suggestion CapLeaker...

[R_J]

Re: Samsung UN50NU6950FXZA ( All In One )

There was another thread on this board, they had a shorted Blue cap CM821, CM822, have a look at them to see if one is cracked or shorted, other than that I would also suspect bad bga's on the large ic.
It likely does not apply here, but here is the thread https://www.badcaps.net/forum/showth...ht=bn96-49483a

[TVAddict]

Re: Samsung UN50NU6950FXZA ( All In One )

Yeah, Thanks R_J i did see that thread earlier, useful info indeed, the blue caps seem fine on my board, not shorting or cracked.

Made an error in checking backlight test points, turns out i do have voltage at the " Discharge " testpoint which ranges from 185 - 210v ( my test leads was not properly touching test points because of shiny coating on the board) also rechecked the led + and led - testpoints definitely no volts there.

Continued probing around, happened upon a suspicious reading on a 10uf 50v cap next to ic 9101, the voltage keeps fluctuating between 0.6v - 4.5v and sometimes reaches 5v, checked the cap, it's perfect, traced cap leads to ic 9101 ( SLM4683A ) goes to pins 6 and 7 gnd and positive, tested the voltage at the ic and it fluctuates the same way, the only other voltage i get on the ic is at pin 1 which reads a steady 12v does not fluctuate.

googled the IC number but no datasheet seem to exist, from what i can make of it's location on the board near the backlight area i'm assuming it has something to do with that but not 100% sure.

Can anyone say what this IC does?
Do you think i'm on the right track with respect to the fluctuating 5v on pins 6 and 7 of the IC, wish i had a SLM4683A to change and see what happens.

[CoppellTVRepair]

Re: Samsung UN50NU6950FXZA ( All In One )

For anyone reading this thread I do not think you are on the right track looking into SLM4683A for the problem you describe.

The IC is an inverter driver as can be easily guessed if you look the area of the board it's occupying - it takes the rectified 13V output out of secondary of the main transformer and drives two MOSFETs , which in turn take power from another secondary through bridge rectifier.

I *guess* it may be possible for one to see what you're seeing with a certain defect in the IC, but what I've seen is two extreme conditions only - working or totally dead board (no output voltage whatsoever).

[howardc64]

Re: Samsung UN50NU6950FXZA ( All In One )

Fixed one of these but not your symptom. Mine had 2 bulgy caps. But seems a few do fail this way so might be a weak point for reference.

https://www.badcaps.net/forum/showthread.php?t=106205

Last post correlates the squeal to the 2 backlight inductors.