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Old 11-24-2021, 12:03 AM   #1
CityZen
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Default Samsung un48ju6700 half screen ghosting problem

This curved LCD TV has an issue affecting just the right side of the screen. It is not a backlight issue, although it might appear so from one of the attached images. The problem appears to be the right side of the screen not updating properly. Moving images on the very right side will leave a trail of ghost images. Although even just the computer cursor sitting still makes a vertical ghost band the entire height of the image. The color on the right side also looks like it doesn't have the full bit depth (the Windows background looked kind of dithered on that side).

I went into service mode and ran the various image tests, but all of them showed the same kinds of issues as mentioned.

Is the problem likely to be the T-con board, or the boards that connect to the bottom edge of the LCD itself, or something else?

Things I tried already (with no effect):
- swapping the left/right FPC cables between the T-con board and bottom edge boards.
- swapping the FPC cables that join the outermost bottom edge boards.
- undoing/redoing the clamps on the FPC cable between the main board and T-con board.
- gently pressing along the bottom edge boards and FPC connectors.

The pink star pattern is this image: https://support.lensstudio.snapchat....D0EBiX_5yg.gif
that I just magnified until it filled the screen. It's not so obvious in the picture, but on the TV, the color is very faded on the right side.
Attached Images
File Type: jpg 20211123_215732-s.jpg (146.6 KB, 26 views)
File Type: jpg 20211123_222011-s.jpg (127.1 KB, 33 views)
File Type: jpg 20211123_215911-s.jpg (230.3 KB, 20 views)
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Old 11-24-2021, 12:09 AM   #2
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Default Re: Samsung un48ju6700 half screen ghosting problem

Here's another picture I'd taken. Notice how the letters "HDMI" get smeared up and down the right side, as well as the disappearing background.
Attached Images
File Type: jpg 20211112_211346.jpg (364.2 KB, 26 views)
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Old 11-24-2021, 12:51 AM   #3
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Default Re: Samsung un48ju6700 half screen ghosting problem

It's a bad panel but there may be a workaround. If it has side tabs on the bad side, you can try ripping them all off.
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Old 11-24-2021, 02:27 AM   #4
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Default Re: Samsung un48ju6700 half screen ghosting problem

Bad panel pull off side tabs it may work
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Old 11-24-2021, 11:38 AM   #5
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Default Re: Samsung un48ju6700 half screen ghosting problem

removing the side tabs is not the best way, its like a finger amputation or similar, check the near thread of Ancient1.
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Old 11-25-2021, 12:43 AM   #6
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Default Re: Samsung un48ju6700 half screen ghosting problem

From looking at Youtube videos of repairs of Samsung TV's of similar vintage, it seems like there are only tabs on the bottom of the screen.

(This TV has 60 sets of plastic clips that hold the front bezel and rear metal to the LCD assembly, and I can't see the sides of the LCD without undoing all those.)

The tabs on the screen bottom have no test points. There are COF driver ICs, but again nothing to problem on the flex either.

Is it possible that the outer pair of tab boards are the horizontal drivers?
Attached Images
File Type: jpg 20211123_220220-s.jpg (387.0 KB, 17 views)
File Type: jpg 20211123_215911-c.jpg (142.1 KB, 11 views)
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Old 11-25-2021, 06:14 AM   #7
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Default Re: Samsung un48ju6700 half screen ghosting problem

Yes much probably you don't have side tabs, so the only way if i'm right is to block clock lines or start signal to the bad side..
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Old 11-26-2021, 06:33 PM   #8
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Default Re: Samsung un48ju6700 half screen ghosting problem

Yes, I just now understood what you meant after trying the experiment I mentioned.

If I leave the outer bottom board disconnected on the problematic side, the result was not as interesting as I hoped: the whole screen fails to show any image.

I did try various experiments masking out some of the connections, and they did make certain vertical bands of the screen display improperly.

After thinking about the way LCD screens are driven, I realized that the horizontal rows are only driven by timing signals, whereas the vertical columns are driven by pixel data.
Only two signals are needed for the rows: the clock (count) and start (reset) signals you mentioned.

I may try some more masking to see if I can isolate them on the joiner flex cable, but it's kind of tedious. A glass workbench would be helpful, so I don't have to keep lifting the TV up and setting it back flat again each time.
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Old 11-27-2021, 12:13 AM   #9
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Default Re: Samsung un48ju6700 half screen ghosting problem

it is needed a photo of tcon board without eventual metal frames
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Old 11-27-2021, 12:39 AM   #10
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Default Re: Samsung un48ju6700 half screen ghosting problem

T-Con:
Attached Images
File Type: jpg 20211124_221621-s.jpg (874.6 KB, 15 views)
File Type: jpg 20211124_221843-s.jpg (625.4 KB, 9 views)
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Old 11-27-2021, 08:15 AM   #11
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Default Re: Samsung un48ju6700 half screen ghosting problem

Remove the sticker and do a photo of that connector area without flash reflection
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Old 12-04-2021, 11:47 PM   #12
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Default Re: Samsung un48ju6700 half screen ghosting problem

Okay, took a while, but here are better T-Con pictures.
Also, I removed the bezel, and discovered there are side tabs.
Attached Images
File Type: jpg 20211203_191216-s.jpg (1.01 MB, 5 views)
File Type: jpg 20211203_185739-s.jpg (615.1 KB, 2 views)
File Type: jpg 20211126_201222-s.jpg (139.7 KB, 8 views)
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Old 12-05-2021, 02:13 AM   #13
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Default Re: Samsung un48ju6700 half screen ghosting problem

Follow the near discussion of Ancient1, there are all the directives..
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Old 12-05-2021, 10:27 PM   #14
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Default Re: Samsung un48ju6700 half screen ghosting problem

Okay, so if I understand you correctly, you are saying that the right side of the screen is missing either the VGL or VGH drive voltage, and that it might be possible to fix that by measuring the testpoints on the side tabs to look for these voltages, find out where it is missing from (compare left and right sides), and then to find a source of the missing voltage (either on Tcon or bottom drive boards) and wire it to the lowest test point where the signal is missing from. Is that right?
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Old 12-06-2021, 02:18 AM   #15
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Default Re: Samsung un48ju6700 half screen ghosting problem

It is right except that you better wire it on distribution board not tcon..
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Old 12-29-2021, 06:53 PM   #16
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Default Re: Samsung un48ju6700 half screen ghosting problem

Okay, so I wasn't able to get back to this set until this evening.

I measured the voltages on the lowest tabs on the left and right sides. I was able to find 26V and -6.6V on both sides. I'm not sure what to conclude from this.
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Old 12-29-2021, 07:27 PM   #17
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Default Re: Samsung un48ju6700 half screen ghosting problem

This is probably due to right side gate COF tab (one of them shorted) issue. I recently repaired a 4k one (Symptoms: right side dark and slow motion image) and I had to remove all the right side COF tabs to get the panel to working correctly. You need to have side COF tabs on both sides of the panel to do that, otherwise this trick won't work and you surely end up with totally useless panel. After removing tabs picture might show little bit discolored (which happened to me in my case) on the right side but only a very sharp eye would notice that. That happens because after removing one side COF tabs the other side's COF tabs has to do all the gate driving on both sides and most of the time they are bit weak for that. Here are some videos that might help you.
https://www.youtube.com/watch?v=c2d68zLWVc0

https://www.youtube.com/watch?v=l5Xx6__1CP0&t=68s
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Old 12-30-2021, 06:50 AM   #18
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Default Re: Samsung un48ju6700 half screen ghosting problem

I can only add to what the previous user said, talking simple, try to cut the vcc that feeds right gate cofs, then turn tv on, then off, join back the cutting, turn again on and hope for the image to come back and good..before this is useful save all tcon eproms content..
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