LG LCD 47LD520 - Intermittent horizontal black lines with 'shift'


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LG LCD 47LD520 - Intermittent horizontal black lines with 'shift'

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Pauley
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Sep 14, 2015, 8:03 PM

Post #1 of 6 (2292 views)
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LG LCD 47LD520 - Intermittent horizontal black lines with 'shift'	Can't Post

Hi there,
I have fairly good debug/repair skills, but was hoping for some insight on this one, since I typically do not repair TVs.

I have an LG 47LD520. Everything was fine and then this issue appeared:
1) Screen looks fine (except for three horizontal black lines about 1/3 from the top)
2) ~1.5 seconds later, some lines on about the bottom fifth of the screen turn black, but they appear shifted above where they should be and also stretched a bit (i.e. the black lines are about 1 out of every 3 on the bottom fifth, and then they appear on the next 2/5th and 3/5th of the screen, so it is not a linear shift of the lines). The affected lines are flickering very quickly, so you can tell it is not a solid signal.
3)~ 2 seconds later it goes back to step 1 and repeats.

This appears on every input and with the menus on.

I took the TV apart to see if I could see any obvious issues (blown parts, vented caps, etc.) and saw nothing.

Here is the interesting piece that may help someone diagnose, or at least give me some insight. There are two flex cables running from the main board to the panel. When I unplug just the left cable, the left side of the TV is solid white (as expected) but the right side shows the expected image, but it is rock steady. No more of the black horizontal lines at all. When I unplug just the right cable, the right side is white, but the problem is present.

I swapped cables and it did not follow the cable, so the cables are good. I also cleaned the cables and connectors.

So, the panel is probably fine, since I am able to get half of the screen to be steady. I think I narrowed down to either the main board or the panel circuitry that the flex cable attaches to (tcon, which is sandwiched in some metal along the top edge of the tv - could not find an easy way to access that board).

What confuses me is why would a signal from the left side affect both sides of the display. I'm sure there is an obvious answer for those that know which signals go to which cable, but it really seems like the left and right signals are pretty independent and just handle each side of their screen. But, there is obviously something from the left side cable that causes issues on both sides of the screen.

Thoughts/Ideas?

Thanks,
Pauley

(This post was edited by Pauley on Sep 14, 2015, 8:11 PM)

jts1957
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Sep 14, 2015, 9:40 PM

Post #2 of 6 (2286 views)
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Re: [Pauley] LG LCD 47LD520 - Intermittent horizontal black lines with 'shift' [In reply to]	Can't Post

Boards along edge of panel are Grid / Source drivers. Shielded board that receives connection from the Main Board is Tcon.

As Shop Jimmy says next to all their tcons: Horizontal lines on the screen are virtually NEVER caused by a bad T-con board. Horizontal lines indicate a defective LCD panel (screen).

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Pauley
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Sep 14, 2015, 11:11 PM

Post #3 of 6 (2282 views)
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Re: [jts1957] LG LCD 47LD520 - Intermittent horizontal black lines with 'shift' [In reply to]	Can't Post

@jts1957: Thank you for your response. I saw a video of a Samsung (?) TV and the guy showed a tcon that was along the edge, which looked like my LG.

For clarity, the flex cable connects the main board to the two boards on the edge of the TV. So, does the main board always connect to tcon (and thus these are tcons along the edge), or is a tcon sometimes 'skipped' or integrated so that on my tv the main board connects directly to the grid/source drivers?

However, it seems like it may be a moot point since it appears a general rule of thumb is that horizontal line issues just about always are tied to a bad panel. I had done some research, and it seemed that was primarily relevant if the horizontal lines were consistent. Mine are not.

Just want to make doubly sure before I throw out the unit and try to sell the other components on ebay (could probably make about $200 to help fund the replacement).

I am tempted to try swapping the left and right outputs to see what happens, but I don't know if the signals would match - best to not play around like that.

Thank you, again,
Pauley

jts1957
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Sep 14, 2015, 11:41 PM

Post #4 of 6 (2280 views)
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Re: [Pauley] LG LCD 47LD520 - Intermittent horizontal black lines with 'shift' [In reply to]	Can't Post

See if this helps: http://elektrotanya.com/...1b.pdf/download.html

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Pauley
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Sep 17, 2015, 2:42 PM

Post #5 of 6 (2253 views)
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Re: [jts1957] LG LCD 47LD520 - Intermittent horizontal black lines with 'shift' [In reply to]	Can't Post

Thank you for the pdf link. It shows that I cannot swap the flex cable. Oh well, didn't think it would work, but know I know.

Interestingly, the exploded diagram does not match my tv since it does not show the power motherboard that my tv has. Also, it did not show the boards along the edge of the tv, so I guess it just considers them to be part of the panel.

Quote

Boards along edge of panel are Grid / Source drivers. Shielded board that receives connection from the Main Board is Tcon.

Okay, I am thinking those boards along the edge that the flex cables plug into from the main board are Tcon. They are definitely shileded and I can see some EMC foam gasket used to connect the board to the shielding.

Since the horizontal lines are probably not the tcon, that leaves the panel or the mainboard. I wish I could get more definitive, but what does your gut tell you on this? Remember, when I have just the right flex cable plugged in, all of the horizontal line issues go away and the screen holds a solid image (granted with the left half being solid white). I'd hate to spend $100+ on a new main board and be wrong.

Pauley

jts1957
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Sep 17, 2015, 3:47 PM

Post #6 of 6 (2251 views)
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Re: [Pauley] LG LCD 47LD520 - Intermittent horizontal black lines with 'shift' [In reply to]	Can't Post

Could be a difference in suffix:
LG Electronics/Zenith 47LD520-UA.AUSWLVR
LG Electronics/Zenith 47LD520UAAUSWLUR

http://www.shopjimmy.com/lg/47ld520-ua

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