Samsung UE32D4003BW Backlight problem.

[Gemat]

Hi,

I have a relatively new Samsung UE32D4003BW TV with not many hours of service that has a problem with the backlight.
When the TV starts, the backight lits to normal brightness, but after a few seconds the brightness drops and the leds flicker.
If the TV stays on for half an hour or so, the brightness gradually increases and the TV works fine for as long it stays on.
I tryed factory resetting the TV.

I send the boards to a local service store and they said it is a mainboard problem and cannot be fixed....

Here is a short video of the problem...

https://youtu.be/lkanGgAyHzo

Any ideas??

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

Here are a couple of closeups near the led output socket....

[yohnsee]

Re: Samsung UE32D4003BW Backlight problem.

Hello,
do you have a multimeter? Maybe an oscilloscope?
First I would measure the LED+ to LED- (I don't see from here, are there only 2 wires going to the LED stripe?)
You need to see, if the voltage fluctuates also, or is it just the leds? Then you should measure the driving signal, is it stable?

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

Hello,
do you have a multimeter? Maybe an oscilloscope?
First I would measure the LED+ to LED- (I don't see from here, are there only 2 wires going to the LED stripe?)
You need to see, if the voltage fluctuates also, or is it just the leds? Then you should measure the driving signal, is it stable?

Hi,
I do have both a multimeter and an oscilloscope .
When the tv starts the voltage is 130 volts and the back light is correctly lit.
After a few seconds the voltage drops to 80-90 volts and the leds flicker and the brightness is low...

[budm]

Re: Samsung UE32D4003BW Backlight problem.

Try turning down the backlights level to as low as possible to see if it will stop flickering.

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

Try turning down the backlights level to as low as possible to see if it will stop flickering.

Do you mean lowering the backlight from the tv menu?

I have already done that. When to voltage is at 80 volts or below, changing the brightness from the menu makes no difference...

[budm]

Re: Samsung UE32D4003BW Backlight problem.

Backlights level is not the same as Brightness (for Video) level.
BTW, the Voltage on the LED connector pins should be measured with ref. to chassis GND.

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

Backlights level is not the same as Brightness (for Video) level.
BTW, the Voltage on the LED connector pins should be measured with ref. to chassis GND.

The measurements I took were between the two cables going to the led stripe.
After half an hour or so the voltage gradually increases to 120 and the backlight is correct.

The intense flicker happens at around 100 volts.

I didn't think of checking the output with the oscilloscope ...


I will check it and let you know.

Thanks for looking into my problem...

[budm]

Re: Samsung UE32D4003BW Backlight problem.

You need to check the LED+ with ref to GND when it is acting up, the LED+ is the Anode of the LED string which is fed by the boosted Voltage from the boost converter circuit.

[budm]

Re: Samsung UE32D4003BW Backlight problem.

BTW, if you disconnect the cable between the power supply and the main board then apply power to the TV, the backlights should come on right away and stay on without any flickering, if that is the case then the power supply and the LED backlights are OK.

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

BTW, if you disconnect the cable between the power supply and the main board then apply power to the TV, the backlights should come on right away and stay on without any flickering, if that is the case then the power supply and the LED backlights are OK.

I will try it on Monday and get back to you...

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

BTW, if you disconnect the cable between the power supply and the main board then apply power to the TV, the backlights should come on right away and stay on without any flickering, if that is the case then the power supply and the LED backlights are OK.

This is exactly what happens.... The leds come on and stay on!

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

So, the local service was right that it is a mainboard issue....

Can I do anything about it? Like force the psu to output a fixed 120 volt to the leds so I can use the TV? I dont mind if I cannot change the brightness from the TV menu....

[vinceroger69]

Re: Samsung UE32D4003BW Backlight problem.

on the power supply theirs a pin on the connector marked blu on/off does that voltage change when the set is powered on test it in standby and set turned on im wondering if this is the voltage that tells the mainboard too turn the back lights on

[budm]

Re: Samsung UE32D4003BW Backlight problem.

If all other functions of the main board are OK, then you can try just having the BLU ON/OFF wire disconnected (and may be the dim control wire too) but all the connectors are back in place, after that when you power up the TV you should then see the pictures and all the functions of the TV should work, if not then you have more than just backlights on command signal problem.

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

Here is another find....

The pin 14 on the main board (Dim_Out) , outputs 1V volt when I turn on the TV, but drops to 0,3 after a second and stays there.

All the other functions are working fine.

How can I manually output 1 Volt there??

Here two Pictures under and over the board zoomed near the plug.

[budm]

Re: Samsung UE32D4003BW Backlight problem.

So right now you are able to get the backlghts to come on and able to see image on the screen, and get sound, etc. correct?
If you go to on screen backlights level adjustment (DIM), can you set the backlights level at all?

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

So right now you are able to get the backlghts to come on and able to see image on the screen, and get sound, etc. correct?
If you go to on screen backlights level adjustment (DIM), can you set the backlights level at all?

I have cut the Dim_Out cable from the board to the PSU and I have reassembled the TV .
The TV works with max backlight, a solution that is not perfect, but I am OK with...

All the other settings except brightness, like sound, colour, etc. work fine....

[budm]

Re: Samsung UE32D4003BW Backlight problem.

So let me get this correctly, if the dim wire is not cut, you will not get the backlights either? What Voltage do you get on the DIM pin of the power supply board?
There are ways to dim down the backlights level to make the LEDs last longer.

[Gemat]

Re: Samsung UE32D4003BW Backlight problem.

So let me get this correctly, if the dim wire is not cut, you will not get the backlights either? What Voltage do you get on the DIM pin of the power supply board?
There are ways to dim down the backlights level to make the LEDs last longer.

If the wire is not cut,
when I turn on the TV it outputs 1volt and the leds lit full.
after a second or two the voltage will drop to 0,3volts and the leds lit very low...

If the wire is cut, the leds lit full all the time...