LG 42LN5200 Vertical Line

[DOPPLERBOB]

Hi All,
I am attempting to get the above mentioned set working. It has a July, 2013 date code and I purchased it on Black Friday, 2013. The original problem was a dark screen ( no backlight ) but everything else was normal. I determined it was the LED's at fault so I took it apart down to the LED's , tested each LED with my DVM on the diode test range so the LED"s would light up, and found one open LED. I tried reflowing the solder pads going to the LED just in case it was just a bad connection, but no luck. So I "bypassed" the LED using 5 1N4004 diodes in series. Bango, the LED's now light and the wife brings out the champagne. But I say not so fast. Lets wait until it is all together before we celebrate. So I reassembled everything back to just short of putting the back cover back on. I fire up the TV and darn, there is a 1/4 inch vertical line directly in the middle of the screen. The rest of the picture is perfect. I wonder if I damaged the LCD Panel? I tried re-seating the flex connectors going to the T-Con board, cleaned the contacts with meth, and even took the whole thing apart again to make sure the flexprints going to the panel didn't get crimped or something. Before I part the whole thing out I wanted to see if there was anything else I can to to verify for sure that the Vertical line is because of a damaged LCD. Any other things I can eliminate? Any ideas would be appreciated.
Bob

[Hamie]

Re: LG 42LN5200 Vertical Line

Check the COF where the black line is? have you ripped it or lifted it by mistake.

[DOPPLERBOB]

Re: LG 42LN5200 Vertical Line

I imagine COF is the flexprint that goes from the small PC boards directly to the LCD? If so, yes I checked them when I took the whole thing apart the second time. They looked OK, but I am wondering if there is a small tear that I cannot see internally. Maybe one of the traces inside the print? Is there any other troubleshooting I can do, such as what to expect if I lift the ribbons to the T-Con ect. and if they would eliminate anything else it could be. I have no way to fix and bond new prints going to the screen so if that is what it turns out to be then it will be lights out and put the champagne back on ice for the next celebration.

[dick_barton]

Re: LG 42LN5200 Vertical Line

I assume you disconnected the panel from the Tcon board when you worked on it by flicking up the connector tabs on the Tcon connectors to remove the ribbon cables.

Reseat the ribbons again and ensure that they are correctly seated before closing down the flaps.

[DOPPLERBOB]

Re: LG 42LN5200 Vertical Line

I assume you disconnected the panel from the Tcon board when you worked on it by flicking up the connector tabs on the Tcon connectors to remove the ribbon cables.

Reseat the ribbons again and ensure that they are correctly seated before closing down the flaps.

Yes sir, I did disconnect those ribbon cables when I took everything apart. I re-seated them several times hoping that it might correct the line. I also cleaned the connectors with meth ( I use methanol solution also on camera sensors because it doesn't leave residue behind).

[dick_barton]

Re: LG 42LN5200 Vertical Line

If you apply careful pressure where the ribbon joins the panel or on the IC in the middle of the ribbon does the line go?

[JeffJ]

Re: LG 42LN5200 Vertical Line

Yes sir, I did disconnect those ribbon cables when I took everything apart. I re-seated them several times hoping that it might correct the line. I also cleaned the connectors with meth ( I use methanol solution also on camera sensors because it doesn't leave residue behind).

The ribbons that go from the tcon to the panel, can you remove them and inspect the pad contacts. I have seen when seating them that a pad on the ribbons becomes sheared off, lifted and/or bent to the side and shorting another. I've done it my self.

[DOPPLERBOB]

Re: LG 42LN5200 Vertical Line

If you apply careful pressure where the ribbon joins the panel or on the IC in the middle of the ribbon does the line go?

Yes I tried that for quite sometime. All 6 of the ribbons that go to the panel and to the 2 thin PC boards along the bottom rail. I rubbed them all while watching the screen- the line never changed. I came to the conclusion that it is the LCD internally itself? Don't know if that could be it or not.

[DOPPLERBOB]

Re: LG 42LN5200 Vertical Line

The ribbons that go from the tcon to the panel, can you remove them and inspect the pad contacts. I have seen when seating them that a pad on the ribbons becomes sheared off, lifted and/or bent to the side and shorting another. I've done it my self.

I will have to look at that closer and see. Thank You for that suggestion.

[DOPPLERBOB]

Re: LG 42LN5200 Vertical Line

All ribbons look fine. Both the ribbons and connector pins all look good under a mag glass. I swapped ribbons with same result. Guess the problem is the panel itself. Oh well I was so excited when I found the bad LED and bypassed it, and got the backlights to work. Guess I was too rough taking the panel apart to get to the backlights. Can't believe LG doesn't get a class action suit for this problem. This TV is barely 3 years old.
Off topic but does anybody have the correct approximate Backlight, Brightness, and Contrast settings I should set my NEW TV for to prevent this?
Bob