[ABORTED] Samsung UN46D6400 No picture, backlight is on


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[ABORTED] Samsung UN46D6400 No picture, backlight is on

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mattkorz
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Jul 8, 2013, 11:25 PM

Post #1 of 18 (16428 views)
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[ABORTED] Samsung UN46D6400 No picture, backlight is on	Can't Post

I have a Samsung UN46D6400 tv that currently powers on (the red led in the lower-right turns off and blinks when I press buttons on the remote), but will not display a picture. The backlight is on (checked in a dark room, it glows the same as it always did).

I bought it 2 years ago, so it's out of warranty. I've opened the back, to see if it was just a loose connection, but it appeared as it should. I looked at the capacitors on the power board, and none of them are bulging, and the fuse on that board measures no resistance. As such, my prevailing hypothesis is that the LCD control board is dead.

Unfortunately, I don't repair lcd stuff enough to know for sure what else I should check. I would appreciate any direction you could give me towards definitively finding out what the cause of the issue is, or if you agree that the LCD board sounds like the likely culprit,

If needed, You can view pictures of the tv with the back off here:http://imgur.com/a/GYSTM

(This post was edited by mattkorz on Aug 28, 2013, 3:19 AM)

mattkorz
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Jul 12, 2013, 3:18 AM

Post #2 of 18 (16395 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Update: Received the new LED control board and put it in place. No dice, the LED screen remains black.

Would a bad main control board cause this? Would a bad main control board still correctly interpret power on/off commands from the remote?

board repairs
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Jul 12, 2013, 4:39 PM

Post #3 of 18 (16386 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Was it a new board or one purchased off ebay or harvested ? Also did the fuse blow on the new board after u installed it or is it ok . You didn't mention but do you get sound from the TV ? Yes the Digital main could be your problem & the remote operations still should function ok . Could also be the LVDS cable or panel problems too . Most of the boards have voltage printed next to the connectors on the boards . Have you checked to see if any are not present or low ? You could also try to put a new fuse on the old board to see if that takes care of it . <br>

(This post was edited by board repairs on Jul 12, 2013, 4:41 PM)

mattkorz
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Jul 12, 2013, 9:29 PM

Post #4 of 18 (16372 views)
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Re: [board repairs] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

It was an ebay board.

The new board and the old both had intact (near 0 resistance) fuses. I only saw the 2 fuses: one rectuagular on the LED board (intact), and one on the power supply AC in (also intact). Are there others?

I just checked the voltage levels on the LED board, it was 12.7 VDC at the fuse. This matches the 12.5v/5a printed on the pcb.

I checked pin-to-pin conductivity of the ribbon cable, and it seemed fine.

74f100
Enthusiast

Jul 13, 2013, 12:02 AM

Post #5 of 18 (16369 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

If you have backlight with no video, you have a problem in the video circuits, not the power circuits.

You can check the fuse on the timing control. It is usually a very small "pico" fuse placed near where the LVDS cable connects to the T/C. If it isn't open, then you would need to trace the video with an O-Scope.....Or start replacing parts in sequence.....But this can get very expensive real quick.

Jim
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mattkorz
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Jul 13, 2013, 12:35 AM

Post #6 of 18 (16367 views)
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Re: [74f100] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

I checked that fuse (I called it the LED control board fuse above), and it was closed. I don't have a scope, nor do I know what the signal should look even if I did: so I think that avenue is closed to me.

I found a main control board on ebay, so I'll give that a try and see if that works.

mattkorz
New User

Jul 31, 2013, 12:12 AM

Post #7 of 18 (16224 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

I got the new main board, and now I get a SmartTV logo when I plug the tv in, but the screen returns to a black screen after. Of note is that tapping the source button on my remote causes the backlight to cycle off, then on to a brighter mode. The visible logo seems to indicate to LCD is itself undamaged. Are there any additional steps I need to take when replacing the main board (e.g., firmware loading)? Is the new main board DOA?

74f100
Enthusiast

Jul 31, 2013, 2:11 AM

Post #8 of 18 (16218 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Do you have menus on the set?
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mattkorz
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Jul 31, 2013, 2:19 AM

Post #9 of 18 (16213 views)
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Re: [74f100] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Nope, nothing shows up on the screen after the power-on logo.

74f100
Enthusiast

Jul 31, 2013, 3:46 AM

Post #10 of 18 (16209 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Samsung's site is down. Is this one of the models with the FRC? It will be a small pcb located above the main.
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mattkorz
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Jul 31, 2013, 3:55 AM

Post #11 of 18 (16208 views)
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Re: [74f100] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

I don't think so. There are pictures linked in the first post of the thread. Please take a look and let me know if there is.

74f100
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Aug 1, 2013, 2:02 AM

Post #12 of 18 (16186 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

I would tend to believe you've got a problem with the main. However, the only way to know for sure is to scope the video from the main all the way through the timing control at the bottom.

Your initial splash screen would tend to mean you've probably got a good panel, but nothing else.
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mattkorz
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Aug 16, 2013, 10:28 PM

Post #13 of 18 (16061 views)
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Re: [74f100] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Still broken.

I got the RMA motherboard back today, and I got a different response from it than the last one. It has very similar symptoms, but instead of just showing the splash screen: it fades to black (like it just stops getting a signal, and a cap is holding the image). When I hot-plug the black connector ribbon between the motherboard and the lcd control board, I get an image on the screen for a second or two, then it freezes and fades like the splash screen did. When I giggle the ribbon cable on each end, I don't suddenly get the image back, so I'm not really sure what is going on at this point. There are visually no nicks or breaks in the ribbon cable.

74f100
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Aug 19, 2013, 3:19 AM

Post #14 of 18 (16033 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Then the other two options are timing/control and panel.
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mattkorz
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Aug 19, 2013, 3:23 AM

Post #15 of 18 (16032 views)
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Re: [74f100] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

By timing board, do you mean the board that sits between the motherboard and the panel?

74f100
Enthusiast

Aug 19, 2013, 10:34 PM

Post #16 of 18 (16017 views)
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Re: [mattkorz] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

yes. It's called the timing/control pcb.
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mattkorz
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Aug 28, 2013, 3:14 AM

Post #17 of 18 (15952 views)
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Re: [74f100] [ABORTED] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

Unfortunately, replacing that board makes no change in the symptoms.

At this point it has been over a month and a half with the TV down. I've decided to cut my losses and replace the whole unit (with a bigger and better one).

Thanks to everyone for their help and insight. If I ever have a flash of inspiration and get it working: I'll reply here to let you know what happens.

(This post was edited by mattkorz on Aug 28, 2013, 3:14 AM)

74f100
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Aug 28, 2013, 3:26 AM

Post #18 of 18 (15947 views)
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Re: [mattkorz] [ABORTED] Samsung UN46D6400 No picture, backlight is on [In reply to]	Can't Post

These sets can be a real nightmare to troubleshoot video issues. I've got 2 in the shop now, with messed up video. I tried scoping both, and still couldn't come up with a conclusive panel or T/C.

The main is usually fairly easy to isolate out.
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