Samsung le40n71b goes black after 2 sec

[nalle077]

Hello friends. I have a samsung le40n71b that goes black after 2 sec.
I have checked the boards for bad caps or other bad parts but not found any.
Does anyone have a clue what the fault might be or how to diagnose it?. Best regards Nalle

[sordids999]

Re: Samsung le40n71b goes black after 2 sec

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Here are photos of the boards

[budm]

Re: Samsung le40n71b goes black after 2 sec

Does it have the Balancer board? The pictures do not show the whole back side of the board.

[tom66]

Re: Samsung le40n71b goes black after 2 sec

One picture of the whole back of the set would be helpful.

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

One picture of the whole back of the set would be helpful.

Here comes some new photos.
Not always good to take help from the family
Think these are better qaulity
I think the photo of the backside of one of the boards look strange. I have not cleaned anything yet.
Regards Nalle

[tom66]

Re: Samsung le40n71b goes black after 2 sec

Right... would you happen to have a spare energy-saving bulb lying about? (One of those weird twisty/stick things, not an LED-bulb, need a CFL type)

Put it near the "DANGER HIGH VOLTAGE" part of the board (do not touch it or the bulb contacts to the point) and while you plug the set in, check to see if the bulb glows briefly. Check both outputs for the glow. The nearby HV field will make the bulb glow if the inverter is working properly.

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Do you mean like this?
https://cgjax.files.wordpress.com/20...2-rgb-3001.jpg
Do you mean just lay it there? And with everything plugged in as normal?

[tom66]

Re: Samsung le40n71b goes black after 2 sec

Yes, the end that lights up needs to be near the HV parts.
The TV should be turned on/off using standby button, all other parts connected as normal.

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Now I have tested with the lamp.
The lamp glows up exactly the same as the lcd backlight. (only 2 sec)
Have tested on both output cables.
What should I try next?

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Now I have tested with the lamp.
The lamp glows up exactly the same as the lcd backlight. (only 2 sec)
Have tested on both output cables.
What should I try next?

any suggestions for this?

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

any suggestions for this?

Up

[tom66]

Re: Samsung le40n71b goes black after 2 sec

Since both sides appear to be working, it is more likely to be the backlight than the inverter (possibly a bad bulb)

Can you see connector with 12V, LD, GND on it? 6 pins, comes from balance/inverter board.

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Since both sides appear to be working, it is more likely to be the backlight than the inverter (possibly a bad bulb)

Can you see connector with 12V, LD, GND on it? 6 pins, comes from balance/inverter board.

Is this the one you mean. Only 5 pins. I see no connector with 6 pins

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

Is this the one you mean. Only 5 pins. I see no connector with 6 pins

Up

[budm]

Re: Samsung le40n71b goes black after 2 sec

What do you get on LD pin, normal = >11VDC.
Can you take the pictures of the Balancer board without the cover?
You do not see any error code blinking LED?
It may have bad lamp similar to this.
https://www.youtube.com/watch?v=oE6K...eY5Gw&index=66
https://www.youtube.com/watch?v=8oZnSleucJ0

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

What do you get on LD pin, normal = >11VDC.
Can you take the pictures of the Balancer board without the cover?
You do not see any error code blinking LED?
It may have bad lamp similar to this.
https://www.youtube.com/watch?v=oE6K...eY5Gw&index=66
https://www.youtube.com/watch?v=8oZnSleucJ0

I have about 6.5 volt between LD and GND.
And that is all the time the set is switched on.
It does not change when the screen goes black.
It was a very interesting video in the link.
It seems like I have the board he is measuring on to the right on me set.
what to think of the 6.5 volt.
should I test like he did in the video?
I do not have that little test point like he does

[tom66]

Re: Samsung le40n71b goes black after 2 sec

You can try taking your energy saving light and putting it near each of the bulb connectors like in the first test. All light should be roughly the same.
Sometimes the bulbs can fail, other times the little ballast transformers can fail

[budm]

Re: Samsung le40n71b goes black after 2 sec

It is basically the same protection circuit using dual diode (3-pin smd), so you can use the same testing method as show in the Video to look at the DC voltage at the common Cathode of the dual Diode.

[nalle077]

Re: Samsung le40n71b goes black after 2 sec

It is basically the same protection circuit using dual diode (3-pin smd), so you can use the same testing method as show in the Video to look at the DC voltage at the common Cathode of the dual Diode.

I have tested with the lamp and number five from the bottom looks a little darker.
I took a photo in the dark and there it is visible to just before it shuts down the light.
I will try the dc test tomorrow.

Edit: number 5 from the right. The photo became wrong way.