SMPS schematic for Samsung UN46EH5000?

[ngth82]

Good evening all!

I'm currently working on a Samsung UN46EH5000 TV.

I'm looking for the SMPS schematic for it. Does anyone have a source they can point me to? I looked on ElektroTanya and Tom's Service manual's sites, but i didn't see it.


I got the TV for $10. The unit worked, but 26 of the 44 back light LEDs were blown (all shorted). Looks like that is common with this model. Using my LED tester, it shows a Vf=2.6-2.7V.

I replaced all of the LEDs with SMD parts that I have. The rated Vf=2.9V on these units.

Right now, the backlight momentarily blinks on (all of them), then the supply shuts off. The backlight controller is a "SLC1012C" -- looks like this is equivalent to a Fairchild FAN7340.

Instead of finding lower forward voltage white LEDs, i'm hoping to just bump up the overcurrent protection of the SMPS board.

Any leads on the SMPS schematic would be appreciated. (if there are no leads i'll just end up replacing the LEDs).

[CapLeaker]

Re: SMPS schematic for Samsung UN46EH5000?

I wouldn't trust any of these old LED's, since they were over volted hard. If there would have been only a couple LEDs bad, Ok... replace them. But that many, just replace all stirps. Other than that, the rest of the old LED's will fail one by one and you won't be happy.

[ngth82]

Re: SMPS schematic for Samsung UN46EH5000?

I wouldn't trust any of these old LED's, since they were over volted hard. If there would have been only a couple LEDs bad, Ok... replace them. But that many, just replace all stirps. Other than that, the rest of the old LED's will fail one by one and you won't be happy.

I ended up replacing all 44 from the LED strips. Yeah, no way I'm trusting the rest of them to work in the long term. Just need to find the correct Vf rated LEDs or the SMPS schematics time adjust the current limit.

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

"Using my LED tester, it shows a Vf=2.6-2.7V." that is what you will see when you only drive the LED at about 30mA, so the Vf of the LED is not the problem, Vf will be higher at higher If.
What is the current rating of the replacement LED?
What is the power supply board P/N? BN44-?????
Pictures of YOUR board?

[ngth82]

Re: SMPS schematic for Samsung UN46EH5000?

"Using my LED tester, it shows a Vf=2.6-2.7V." that is what you will see when you only drive the LED at about 30mA, so the Vf of the LED is not the problem, Vf will be higher at higher If.
What is the current rating of the replacement LED?
What is the power supply board P/N? BN44-?????
Pictures of YOUR board?

Hi Budm -

I'll get you the board info and pictures when I'm back in town. Currently out for a business trip. No TV joy at the moment.

The LED rating is attached. I bought a 100 two years ago.


Thank you as always,
Thomas

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

I do not see the If rating.
Vf typ. of 3.4V at 20mA? That cannot not right for backlights LED.
See Vf VS If graph sample, this example is rated at only 0.5W, most backlights use 1W LED.

[ngth82]

Re: SMPS schematic for Samsung UN46EH5000?

Hi Budm - unfortunately, that screenshoot is the only information that I have for this LED.

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

I won't trust that seller spec, if that is all the seller can provide.
Boards:
https://www.shopjimmy.com/catalogsea...ung+UN46EH5000

[neilc6]

Re: SMPS schematic for Samsung UN46EH5000?

Samsungs do not have protection shutdown on the power supplies and the leds will continue to fail until they all short out, there is an open in the string, or the power supply is damaged. I would replace all strips with new. Never seen backlights flash on a Samsung model. Probably an intermittent LED going open in the string.

[arizanotlari]

Re: SMPS schematic for Samsung UN46EH5000?

Hello.

https://www.arizanotlari.com/znl193-ariza-notlari.html this board also using FAN7340. If backlight blinking add 100K resistor to pin 13 of FAN7340.

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

You can experiment by driving one of your replacement LED at about 200mA with DC power supply and see what happen.

[arizanotlari]

Re: SMPS schematic for Samsung UN46EH5000?

i do it all time with this (znl193) board.

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

Hello.

https://www.arizanotlari.com/znl193-ariza-notlari.html this board also using FAN7340. If backlight blinking add 100K resistor to pin 13 of FAN7340.

Pin 13 is the OVP for Boosted output Voltage protection in case there is no load, I.E. LED string has open circuit, so by adding another resistor between pin 13 and GND, that means the trip point of the PVP is moved higher.
So what is the root cause that of the issue that you have to move th trip point higher? May be other resistors in the OVP Voltage divider string has changed i value, or may be the LED string has intermittent problem with circuit go open circuit?

[arizanotlari]

Re: SMPS schematic for Samsung UN46EH5000?

Answer is simple; bypass ovp. i do this many times in grundig/beko tvs.

i dont say connect pin 13 to gnd. i say add pin 13 100K resistor to ovp.
please check diagram https://www.arizanotlari.com/wp-cont...ds/fan7340.jpg

i hope you understand (sorry my english).

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

But that is not a repair, instead of finding the cause of the problem the protection circuit is disabled instead.

[Davi.p]

Re: SMPS schematic for Samsung UN46EH5000?

If you do repair tvs for job it's better to buy at least a very cheap led tester so you can test all the leds with an extetnal supply. From what i've seen in a different schematic but similar, Arizan i think is right 'cause in those boost circuits the OVP pin is the one than rules the Vout, and not a FB pin, so adding a resistor in the voltage divider can rise up some volts to better "fit" the replacement leds, what he doesn't say is if that R is from OVP to gnd or from OVP to Vout...

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

OVP pin is used to monitor the Output Voltage so If it goes too high due to no load it will shutdown the Boost converter, it is NOT for regulating the Output Voltage. So if that pin is trip some how, it thinks that the Voltage is too high. When the protection is not there and the load goes open circuit, the Voltage will go higher that the filter cap Voltage rating.
You lower the resistance between pin 13 and Ground so the Trip point is raised higher, it is just simple Voltage divider resistor network.

[Davi.p]

Re: SMPS schematic for Samsung UN46EH5000?

Those supplies are not at fixed voltage, right? Ovp sets the maximum voltage, since newer leds require little more voltage then Ovp must be set higher..

[budm]

Re: SMPS schematic for Samsung UN46EH5000?

The constant current power supply the LED backlights, instead of vary the supply Voltage output of the Boosted converter to maintain the constant current, it uses low side PWM control element, I.E. MOSFET, on the return side to maintain constant current by varying the Vdrops on the MOSFET to maintain constant current.
The VF of the LED string has to drift drastically high that it reaches the OVP set point.
The application circuit of the FAN 7340 is set to trip when Booted Voltage reach 248VDC, the normal Voltage is 230v, so it has about 18V headroom. I believe the failure is due the resistor network has drifted in value that cause the OVP shutdown point to be lower.

[Davi.p]

Re: SMPS schematic for Samsung UN46EH5000?

instead of vary the supply Voltage output of the Boosted converter to maintain the constant current, it uses low side PWM control element, I.E. MOSFET, on the return side to maintain constant current by varying the Vdrops on the MOSFET to maintain constant current.

I know this, I don't understand "low side PWM control element", if you mean the internal one connected outside with pins "drain" it is OK, but this is not the point, what you say is all OK but since it has no fixed Vout it only uses the Feedback voltage to protect over a certain Vout, so since new leds needs more Vout to work properly, the PSU rises too much Vout to reach the right Iout, then Vovp is reached and PSU stops, i guess if the Poster lowers the backlight brightness using the image with a lamp pointed at, maybe the backlight stays ON. Is it not true?