Samsung 40" 1080p LCD HDTV LE40B750‏ - Flickering Backlight

[Valkia]

Hi Guys,

I was recommended to come here from my local forum. My Samsung LE40B750 has developed a backlight flickering which has gradually got worse. It will flicker until the screen blanks out (image is still there but really really dark).

If I turn backlight off completely then the TV is fine, just darker and not as enjoyable. I'm not the most tech of people with TV's.

I would like some help finding the best possible solution as realistically I don't want to spend too much fixing it. I've been quoted from a local Samsung repair company £48 for them just to take a look, enquired how much pickup of the actual TV is also and that was £48!


Thanks

[JimmysTGP]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

I've seen where companys will start small and then make it up at the end by charging what they really want to make on a job. We charge $60 for inhome, when the guy down the street charges $50. But at the end we both have an amount set for each job. As far as Samsung Backlight issues, its usually Inverters or Panel itself. I have not seen yet where a T-con can hold down the Backlight, but don't throw out the possibility. Without the proper tools it can be challenging to give a good diagnosis.

[Valkia]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Thanks for the reply, yeah it's always seems they add extra here and there. I don't mind paying - Just not if it's going to be worth more than the TV is currently. Just wanting to see if it's a common problem with the same/similar TV and what the most likely cause could be.

[tom66]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Backlight flickering - depends on the topology of the TV - one large inverter, single output, or several smaller ones, multiple outputs.

Can you post some pictures of the insides of your TV?

[selldoor]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

If I turn backlight off completely then the TV is fine,
Thanks

What does that mean you disconnected the backlights or you turned the brightness down using the on screen menu.

And that stops the flicker?

[woodware]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Hi to all. I have Samsung LE37A656 ( Europa). There was no picture on the screen. Found out that on a 100 Hz board a voltage regulator 4435b was out . Zero ohms on the instrument.. Than got 12 volts and the picture.
But, it is flickering. The more intense contrast and light,or bright scenes, more flickering.
If the light and contrast are about 25-30 0n the scale, than no flickering,except darker images. ANy sugestions or ideas? Power supply probelm? T-con?

[ron77]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Had similar problem to yours on samsung tv last year. Reasonably sure Samsung I repaired was same or similar to yours.
Inverter, psu board, on right hand side looking from rear.
Replaced capacitors and resoldered panel. Helped a little but did not effect cure.
Finally, I turned preset at top of panel anti-clockwise a little. After that tv ran for some time without flickering. Did flicker eventually, but an extra anti -clockwise turn cured flicker completely. Felt more like a quick fix than a repair.

An important point, on my set, 4 inv txfmr, top two running hotter than bottom two.
After I had completed what I did, top 3 txfmr ran about same temp, bottom one slightly less. Search this Samsung model on badcaps, and you will find same model with pics.
Remember, though, your set could have different cure to mine.

[woodware]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Hi Ron77,
Thks for reply.
Please explain what is preset at the top???

[woodware]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

I cant see any preset here. Looking from back, the main board, 100HZ are on right side + T-con at the top. The power boar is in the middle and light unit on left. Everything is fixed, no preset is available as I can see. ANy preset on the edge of the panel ,under the metal frame????

[ron77]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

If your tv is same as one I came across, there is a preset pot. at top of inv. psu. board. It is covered with substance that locks it. Proceed with caution if you adjust it. Havn't got setting up proceedure for this potentiometer. Myself, I moved it only a little at a time, watching for improvement in flickering. In my case had no problem. Could be the preset had changed in value, it is possible.

[ron77]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

If you look up Samsung le40b750 on badcaps forum, is set 1 was talking about. Sorry, I always say you learn more from your mistakes than when you get it right.

[woodware]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Hi,
Opened the metal bezel and found the small metal preset. Tried in small steps. No change in flickering . Only some change in brightness of the panel. SO, put it back in start position.

[tom66]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Sometimes there is a jumper, JP852, that can be cut, which can cure this, do you see jumper JP852?

[ron77]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Mr Woodware.

Seems there was misunderstanding. Reason is, takes me so long to write my posts. Didn't see your post, I thought I had made bad mistake, had got model wrong. Didn't know you had entered thread. Only come in on thread when have actually repaired same fault on same model. Reason is, there are many, very good troubleshooters on this forum.If not started already, start a thread with your model no. You stand a good chance of a good outcome. Ron77

[Kado]

Re: Samsung 40" 1080p LCD HDTV LE40B750 - Flickering Backlight

Hello!

My TV has a simmilar issue but instead of the lamps going off they blink brighter.
It starts as a flash every now and then but if I increase the backlight it will start blinking or flickering like mad. If I set the backlight all the way to max (10) it stops and if I leave it there for a few minutes then I can set it back to here it was before (2) with out any more flashes or blinking, for some time.
TV is calibrated with the reference values from this hdtvtest review.

I checked (with some colleagues from work) the IP board for issues like bulged caps and other defects but haven't found anything.

I made a video of the issue but youtube only renders up to 25fps so the issue is visible but not to its real extent, video here.

I've uploaded a 1920x1080 50p version of the video to mediafire here.

Also took some pictures of the IP board that can be found in this firegoon folder.

Hope someone can help me diagnose this!

Cheers!

Kado