Samsung ln40b540p8f flickering

[technicallyartistic]

So I have a model ln40b540p8f, model code ln40b540p8fxza that is flickering at times. It seems to be related to the energy saving mode. It's happened a couple times now. Before going in and changing the settings around from off to low or medium seemed to do it. But the other night with was flashing on and off and none of the settings were making a difference.

I opened it up to see what it looked like inside. I saw some videos online that showed cutting a jumper solved the problem, but it turned out my motherboard was different. I did blow out all the dust from in there which there was a good bit. When I put it back together and turned it on it was working fine. I don't know if that was from removing the dust or that certain parts got discharged.

I'm decent at soldering and have the tools. I've done things like replaced capacitors in a receiver mother board to get it to work again, but I had a decent walk through for that.

Does anybody know what the issue might be and how to solve it? For the receiver I repaired it was under-powered capacitors that didn't have a high enough heat tolerance if I recall, that made the hdmi ports cut in and out. This seems sorta similar, but really that's my only reference to go off of for any similar sort of issue.

Thanks in advance for any advice anybody might have.

[budm]

Re: Samsung ln40b540p8f flickering

Cutting the jumper is not a real fix, all it did is bypassing the protection circuit.
How about uploading the pictures of the whole back side of the TV and the boards so we can see what we are dealing with?

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Sorry for my delay. I was procrastinating on taking the thing back down and opening it up again.

It did it one more time again. My wife needed to take a picture of a QR code on the screen and it wasn't working so I went through all the power settings but that just started the flashing again and nothing worked and it just kept flashing. Just different rates of flashing. I then unplugged it, waited like 30 seconds, plugged it back in and it was still flashing but when I went to the settings I went through all the settings again and came back around to "off" it stopped flashing again.

Anyway, it's not flashing now, but figuring out what's causing it and fixing it would be amazing. Let me know if you need better pictures. My phone takes horrible pictures in low light for some reason now so I can break out the real camera if this doesn't cut it.

[budm]

Re: Samsung ln40b540p8f flickering

What is the P/N of that power supply-inverter board? BN44-?????

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Model: H40f1_9dy
Code No: BN44-00264B
PCB Revision: Rev 1.1
Date: 09.01.18

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Any luck? Still flashing on and off randomly and sometimes going through the settings fixes it and other times not so much. Just happened and leaving it unplugged for the moment to see if it resolves at all.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Ok, I did some more digging and tried what this video suggested. I tried what this video suggested, left the tv on until it started blinking with the back off. I could see it was the back lights. I turned it off an unplugged the t-con board and turned it back on. It was still flashing despite the no video signal. So it looks like its the back light somewhere.

https://www.youtube.com/watch?v=9mHcDbIAQXQhttps://www.youtube.com/watch?v=9mHcDbIAQXQ

The flashing is at a constant pace and the rate is dependent on the energy saver settings. Low is about 2-3 flashes a second while high is a much quicker strobe. I can record a video of that if it helps at all.

So it is like the video says and it's most likely the back lights that I should replace? Like the actual LED lights? Or is it something driving them since they all flash in unison?

[Dangermoose007]

Re: Samsung ln40b540p8f flickering

Backlights are usually long slender boards that run up the length of your panel along the edge. From my experience I would say the backlights are the reason you are seeing the symptoms you are seeing, but not necessarily the CAUSE of the symptom. I would say this is likely a power supply issue, providing insufficient power to the backlights for them to modulate their flashing frequency which provides a dimming effect.

In the case of this TV the backlights are integrated with the power supply into a single board, shown here...so it actually makes no difference lol.
https://www.youtube.com/watch?v=lRHv-whVHOU

I don't see any bulging caps or obvious burn marks to say 'replace that component', but looks like this board can have some issues with the transformers burning out from the CFLs getting old and drawing too much current.

videos on that
https://www.youtube.com/watch?v=EO2gHBJCvH0
https://www.youtube.com/watch?v=PflyJ4H51Fg

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Yeah, from everything I've been reading it seems like the BN44-00264B board would be controlling that. The lights seem fine and they usually work fine for at least a half hour to even a few hours before the flashing starts. And every time the rate seems to be consistent based on what energy saver setting it's on. It also sounds like BN44-00264A, BN44-00264C, BN44-00284A, BN98-01984A boards are a suitable substitute.

I've looked over both sides of the board and haven't seen any signs of damage. The fuses seem good still. Tested some of the other parts based on a general tutorial for testing tvs and things seemed good. I would guess it's under-powered caps maybe that can't handle the heat but even if that was the case I'm not sure what a suitable replacement would be for what the board needs.

Currently I'm looking at just buying one of those replacement boards or shipping off my current one to be repaired, but I wish I could figure out which part of the board was controlling that, or test the caps without desoldering them. That and just trying to make sure that even if I do send it in that that board is actually the problem.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Does anybody know off hand if the ln40b540p8fxza uses CFL or LEDs for it's backlights? I'd assume that would help narrow it down as I wouldn't think LEDs would be drawing more power as they wear out, unless somebody wants to correct me there.

[budm]

Re: Samsung ln40b540p8f flickering

http://www.shopjimmy.com/catalogsear...?q=bn44-00264b
You have CCFL for backlights, and the board is power supply/inverter board combo.
What happen if you turn down the backlights level in the on screen user menu?
What DCV do you have measuring between the two legs of the main filter cap?

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

So as I go down through the settings the the rate of flashing decreases. Sometimes when we get back to off it will stop. Other times it doesn't and flashes about as much as when its on the low energy setting. I'll get a video of this to post when it starts doing it again.

Which cap is the main filter cap? Is it the two large ones?

[budm]

Re: Samsung ln40b540p8f flickering

'Which cap is the main filter cap? Is it the two large ones?' yes.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Both caps are around 159.1 V it looks like.

[budm]

Re: Samsung ln40b540p8f flickering

Both caps are around 159.1 V it looks like.

It should be around 400VDC when TV is turned on, if not then the PFC Voltage booster is not working.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Hah. Right. I meant to turn the TV on before but then I had to run back upstairs to get something and forgot to do that part when testing it. 159.1 is when it's off.
They are both about 383 volts when turned on. Is that high enough?

[budm]

Re: Samsung ln40b540p8f flickering

If it is 360VDC or less then I would worry, so that is not that bad at 383VDC.
Do you know if that 383, is stable when the backlights are flashing or it gets lower when the backlights level is set to max?
It can also be bad lamps connections on the lamp socket or worn out lamps.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

I'll turn it on now and try to get it to do it again. It can take anywhere from a half hour to a few hours to start again when it's been off for a while. I was trying to get it to do it before but then I had to head out for a bit.

[technicallyartistic]

Re: Samsung ln40b540p8f flickering

Ok. Finally got it doing it. On low it was fluctuating between 377 and 381 volts, but mostly going between 378 and 379. And not at the rate of the flashing. Like every few seconds it goes up and down in voltage while the flashing is much faster than that.

On the high energy save settings it's sitting at a pretty steady 380.

With the energy saving setting off it's sitting at a steady 382 now after having been on about an hour.

And here's a link to the video of it flashing.

https://goo.gl/photos/AdgrAn7vZnSMVofk7

So what does that potentially imply?

[budm]

Re: Samsung ln40b540p8f flickering

I think what we need is to look at the ENABLE signal feedding the PWM IC in the Inverter section to see if it is going High and Low when it is flickering.
BN44-00264B
Please get the P/N of UI801.