Samsung LED TV UN55C7000WFXZA no backlight sound is ok

[Yasser]

Hello all,
I am seeking your help diagnose my TV Samsung model UN55C7000WFXZA, the picture and sound working fine but without the backlight, I discounted the cable between main board and power supply the backlight didn't come!

I think the problem is with power supply board, I searched in the database looking for PS diagram model BN44-0376A I couldn't find it.

I am posting few pictures here to let you know the boards and appropriate your advise and help

Thank you

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Another photo for TV part number

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Picture of whole power board?

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Thank you Tom for your reply,

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Right hand connector going to the LEDs in the panel. Using multimeter, with black probe on chassis, and red probe on each pin, what do you see? (use 200V DC range.) Set should be switched on.

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

I checked first with multimeter at 200V DC but all reading are above, please note the following:
1. Pin#1 340 - 360v
2. Pin#2 0v
3. Pin#3 340-360v
4. Pin#4 260-280v
5. Pin#5 0v
6. Pin#6 0v
7. Pin#7 280v
8. Pin#8 0v

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Those are very high readings, though I suppose not impossible for a 55". Please check your multimeter battery is not low. Those readings should give you light from the panel, so you may have an open circuit LED inside the LED-LCD panel.

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

I replaced my multimeter battery today, before start checking

Is there anyway to check if there is an open circuit LED? Is it possible to know from the connector itself?

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

If you have that high voltage and no light, then it must be an open circuit LED, but I am confused. Usually there are four individual strips in a configuration like this. So you should have some light produced, even if it is minimal. Do you have absolutely no light in a dark room?

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

No light at all, although I can see the picture when I am using torch light from top or corner of screen

Also I noticed from the previous reading that pin7 is reading 280v while it's return on the board as N.C not sure if this will help us in any direction?

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

It seems like the LED strings are getting the required voltage so the fault will most likely be with one of them, but very strange that both would fail? Could be a connector issue?

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Tom, what do you think I should do now? Connector look good
By the way I measured the voltage with connector not connected and i got the same readings only in pin 2&3 nothing else

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Sorry pin1 & 3 only showing voltage all other pins are 0

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Are the labels LED_T+, LED_T-, LED_B+ and LED_B- on the connector?
What voltage do you get between T+ and T-, and B+ and B-?

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Voltage as follows:
Between T+ & T- reading various between 0 to 24v
Between B+ & B- reading various between 0 to 60v
These are strange readings I think it should not change?

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

I am thinking that those are what the voltages should appear between and they are not high enough. If you disconnect that connector do the readings change?

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

No change same readings

[tom66]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

I am making the assumption that T+ and T- is the positive and negative of the top LED strip, and that B+ and B- is the positive and negative of the bottom LED strip.

Fast track guide


Try procedure on 2nd page for forcing backlight on. Just to eliminate obscure main board fault.

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Thank you Tom, I followed the procedure but no backlight on

[Yasser]

Re: Samsung LED TV UN55C7000WFXZA no backlight sound is ok

Hello experts, any idea what I can test next?