Samsung UN55D6450 turns itself off and on endlessly, no blinks

[Louis82]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

@Djluis: My tv is fixed. The power supply BN44-00428B doesn't turn on the backlight by disconnecting it from main board. I'm attaching the procedure I followed to get backlights on. Thanks for your time. My tv model is UN55D6450

[djluis]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Disconecting main will turn on backlight led strips, verified.

[Louis82]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Anybody?

[Louis82]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

I have same tv UN55D64 which it plays for a minute, then goes off and comes back on again. I have fully resoldered my power supply as many of you have found loose connections on it but still same issue. I wanted to isolate the problem by disconnection main board from power board but the screen or backlight on this tv do not come on automatically after disconnecting the main board.

So I tried the typical jump on PS-ON to A5V and the power turned on as I get 13V on some of the pins but no backlight. I jumped the BLU-ON to one of the B5V and a huge spark happened to the point that my connector melted a little bit.

Can any of you indicate how I can turn on the Backlight on this tv by using a jump or resistor? I want to test which board is the one that is causing the shut down.

Thank you.

[j8r8mi]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

I had the same issue with my 42 inch TV. I worked on it for a long time and found this thread. I never considered that it could be the LED check. What I did was jumper the connection from the known "good" led to the one having the issue.

It seems unlike the other TVs and checks, including the fast track, this particular TV has each LED driven individually. Referring to post #103 picture, there are two connectors driving each LED, with a positive and negative.

If the Left LED 1 is flickering, L1, (Pins 7 and 5) you can test this by jumping to a known working LED. In my case, L5 was fine, so I jumped Pin 7 to Pin 8 (-) and ping 5 and pin 6 (+). This caused the LED to function normally and prevented the on/off cycle. (And made the TV usable again)

Mine is definitely a power board issue, but I was able to hold off on buying a new one by doing this. Hope this helps and thanks for all of the help.

[withalligators]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Well, I got a little over a year on this thing. LEDs started flickering again yesterday and it won't stay on. Should I try and replace the PS board as well as the LED strip, to prevent this from happening again?

Also, do we think the LED strips are interchangeable from left to right? Or is there some kind of zoning?

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

any way to bypass the backlight LED's functionality check? maybe to simulate somehow the current consumption... at least I could check if that's the issue and everything else works. thanks.

or a schematic for bn44-00427A/B ?

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Don't recall if that was ever explained.

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

ok, so what i understand is that each strip is divided in 4 independently driven sections.

According to the fast-track:

LED Drive Voltages (CNL802 A&B):
1.Positive Pins Lx+ & Rx+: (38Vdc)
2.Negative Pins Lx- & Rx-: (1 ~ 10Vdc)
1.1Vdc = Brighter screen
2.10Vdc = Darker screen

I guess the brightness is controlled via voltage. higher voltage brighter led. So I would think of 4 pairs of LX- and Lx+ for one side strip, but the board has 8 pairs of Lx- and Lx+ for each side.

Any clues why are 8 pairs instead of 4?

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

oh, sorry, didn't notice it at first sight ..

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

does it have a part number? or any kind of identification data on it?

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

See here..

https://www.badcaps.net/forum/showpo...0&postcount=75

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

thanks. do you happen to have pictures of the strip?

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Full strip is easiest IF you can locate one.

Otherwise it is possible to replace single leds if you can find a strip to harvest them from. A bit more involved.

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

I've checked the closest fast-track guide to my model, from Tom's site a UN46D8000, the only thing it mentions is :

Forced Backlight-On Mode:
1. Disconnect Power Cord
2. Disconnect wire harness from CN201
3. Re-Connect Power Cord
4. LED Backlight should immediately turn on

That's what I did when I took the pic and video from my last post. Noticed that the power cycling is the same even without the main connected, so the PSU has some kind of backlight check and restarts the PSU.
I saw the fast track for 55D6900 mentioned in this thread earlier, which is a bit more in details regarding the backlight activation. I guess it's not necessary to apply the jumper wire to those pins, although I do have the same PWM pins on my board.

Now we know the leds are gone. What's next?
how can I replace them?
can be replaced on individual basis ? or the 1/4 length or the full led stripe?

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Yup IIRC this set does have 1/4 length dimming (25 leds) which jibes with what nroberto is seeing.

[tom66]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

It's not real micro dimming, it can just dim regions of the panel, in sections usually 1/2 or 1/4. This allows them to claim sky high contrast ratios which only work on certain specific scenes (such as a sunset, skyline, etc.)

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Find the Samsung Fast Track for this tv and isolate each led section with jumpers and verify the proper way whether you have bad leds before making the decision to go inside.

[nroberto13]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

OK, here's how it look like. tried to take pictures in the dark to see the backlight, but the camera doesn't do quite well . But it-s clear that the top 1/4 is not lit. Here's a video too maybe it's better.

https://www.youtube.com/watch?v=OLWP328jrgM

According to this video ( ~ 14min ) , the tv has micro dimming technology meaning that each led can be independently turned on/off. I don't understand then why is such a long surface not lit, about 1/4 of the side edge, I can't believe so many leds burned out.

some questions ...

did you manage to replace the leds?
where did you find the replacements?
can be replaced on individual basis?
are these normal usual leds?

thanks.

[mmartell]

Re: Samsung UN55D6450 turns itself off and on endlessly, no blinks

Unplug the cable between main board and power board and plug set in. Check the Samsung Fast Track supplement as additional jumpers may be necessary.

The tv powering on after power is applied is simply the main board remembering its last state. No worries.