Samsung U32EH4003 problem.

[HellasTechn1]

Good day people !

I came back to you with a new problem i came across.

I have a Samsung U32EH4003 LED TV that keeps blowing the bottom LED strip.

At first i locaded the burned LED and replaced it, thinking that thiss would be all. After powering it up it blew that LED again.

I disconnected the backlight pwer connector from the PSU and the mainboard power connector and then i pluged in the PSU and measured voltage across pins 1 and 5 of the CNL802 (backlight connector) and it gives me 140V DC.
There are 2 led strips consisting of 9 LED's which in series should require around 54V DC to work. Now no wonder it keeps blowing LED's but why is it giving me such high voltage ?

I have attached pictures for you.

From what i see the D+ comes from the transformet through DM805C diode
and D- from IC9205 or IC9805 (isnt clear) through Q9803C MDD4N20Y mosfet

[dick_barton]

Re: Samsung U32EH4003 problem.

Measure each Led connector pin using chassis as ground and post results please.

Can you also post a focused picture of your power supply so that the legends can be read.

[Andrew F. Ali]

Re: Samsung U32EH4003 problem.

Did you replace the one burnt LED on the strip or did you replace the entire strip? If you had just replace the one burnt LED and not the entire strip, I would think that your replacement LED was not the correct type or the solder connections you made were not properly done. Anyway, for the source LED supply to be burning one set only does not seem logical to me.

[HellasTechn1]

Re: Samsung U32EH4003 problem.

Measure each Led connector pin using chassis as ground and post results please.

Can you also post a focused picture of your power supply so that the legends can be read.

Will do !

Did you replace the one burnt LED on the strip or did you replace the entire strip? If you had just replace the one burnt LED and not the entire strip, I would think that your replacement LED was not the correct type or the solder connections you made were not properly done. Anyway, for the source LED supply to be burning one set only does not seem logical to me.

I replaced only the burned LED. It is of same specs with the rest. As for soldering i can confirm that it's been done correctly since if i power each strip individually with 27V from my bench PSU, all LED's glow.

It was probably just some random reason that burned the same LED.
I beleace that the reason im getting such high voltage is that there is something wrong with the D- side.

[HellasTechn1]

Re: Samsung U32EH4003 problem.

Measure each Led connector pin using chassis as ground and post results please.

Can you also post a focused picture of your power supply so that the legends can be read.

I get 139.1 V from D+ (transformer's side) to chassis and 2.2mV "nothing" from D- to chassis (controller's side).

In the purple bos is the diode that connects the transformer with D+

[dick_barton]

Re: Samsung U32EH4003 problem.

What's your LCD panel make and model number as attached to the metal chassis.

https://www.youtube.com/watch?v=EgRKJAqYqeo

[HellasTechn1]

Re: Samsung U32EH4003 problem.

On the chasis there is a sticker saying Samsung CY-DF320AGEV1H.

made in hungary

[dick_barton]

Re: Samsung U32EH4003 problem.

I can't find any details yet on the panel but I suspect from the shopjimmy video that the problem is with the replacement leds not matching the original.
They are not interchangeable from one lcd set to another but must match maximum current, forward voltage and colour temperature.
The high voltage when the leds are open circuit or connector disconnected appears to be normal as shown in the video.

[HellasTechn1]

Re: Samsung U32EH4003 problem.

That's really weird. I have replaced other samsung TV's burned LED's with the same LED i used here and i had no problem at all. How come it gives 140V open circuited.
Why would the Strip work when i apply 27V from my bench PSU ?

Does it make sense to you ?

How the 140V go down to about 57V for the LED's to work ?

P.S. colour temprature does not match but for only 1 led it's no big deal. forward voltage is the same (i think).

[dick_barton]

Re: Samsung U32EH4003 problem.

The voltage alters because the leds are driven by constant current, let's say 400mA. When there is no current being taken the voltage continues to rise to supply the current until it reaches it's maximum voltage and cannot supply any more voltage.

If it was driving a string of leds let's say at 65V @ 400mA and you added 2 more leds to that string then the voltage required would rise by (2 x 3V) to 71V and still supply 400mA to the leds.

[HellasTechn1]

Re: Samsung U32EH4003 problem.

Okay that makes sense. On the video though he measures 180V on both D+ and D- to chasis while i get 0V from D- to chassis.

[dskall]

Re: Samsung U32EH4003 problem.

They measured D+ to ground not D-

[budm]

Re: Samsung U32EH4003 problem.

So you installed NEW LEDs on to the LED strips, What is the spec of the replacement LEDs?
Some of these 32" SAMSUNG uses 6V LEDs.
Total numbers of LEDs.?

[HellasTechn1]

Re: Samsung U32EH4003 problem.

That's right. I removed the blown LED and soldered a new 3V LED. I am not aware of it's current tating though.
Iv'e used the same on an other samsung and worked fine.
They appear to be 3V led's. It has 2 strips of 9 LED's each.

I'll look for the original led stripe though and see...

Iv'e learned something new here today. The constant current supply used for the LED's.

Are all LED backlight TV psu's like this ?

[dskall]

Re: Samsung U32EH4003 problem.

I am working on same model except for F on end. Some led's are bad. Tested one with led tester. It showed 3.7v at around 300ma. My meter goes from 200ma to 20a so resolution not good. Anode is on small pad. Trying to source some led's for it.

[budm]

Re: Samsung U32EH4003 problem.

That's right. I removed the blown LED and soldered a new 3V LED. I am not aware of it's current tating though.
Iv'e used the same on an other samsung and worked fine.
They appear to be 3V led's. It has 2 strips of 9 LED's each.

I'll look for the original led stripe though and see...

Iv'e learned something new here today. The constant current supply used for the LED's.

Are all LED backlight TV psu's like this ?

Yes, they use constant current circuit to drive the LED, the more current the brighter it gets..
"It has 2 strips of 9 LED's each." so 18 LED total, that is more likely to be 6V LED, I have seen that before in some SAMSUNG panel, you should verify to old working LED Vf rating.
There is label for the LED output Voltage under load, I cannot read it due to poor quality pictures.

[dick_barton]

Re: Samsung U32EH4003 problem.

What you can do is provide focused photo's of the legend on the board. The photo you have provided is not focused.

[budm]

Re: Samsung U32EH4003 problem.

Power supply /LED driver board P/N BN44-??????

[HellasTechn1]

Re: Samsung U32EH4003 problem.

What you can do is provide focused photo's of the legend on the board. The photo you have provided is not focused.

I will focus on the highlighted spots. It's my camera...

Power supply /LED driver board P/N BN44-??????

BN44-00664A

[dick_barton]

Re: Samsung U32EH4003 problem.

Thanks for those. Photo 2 says your led string driving voltage is 65V @ 450mA so the leds are 3V leds.