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Old 07-10-2017, 04:32 PM   #1
engelwood39
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Default LG 55UF6450-UA with white screen

I have a LG 55UF6450-UA that when I turn it on it is just a white screen that does not show any menu or volume text on the screen and is unresponsive to remote commands except power on and power off. What are some things that I should test to try to narrow down the problem?
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Old 07-10-2017, 05:04 PM   #2
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Default Re: LG 55UF6450-UA with white screen

Check on both sides of t-con board fuse for voltage
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Old 07-10-2017, 05:09 PM   #3
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Default Re: LG 55UF6450-UA with white screen

Also to clarify and update after further testing... It is a dim lit screen when I turn it on, not a bright white (1st picture). When I unplug one side of the T-Con it gets bright white on one side (2nd and 3rd pictures). Also I have been able to get volume coming out of the TV from an input. I think that this might mean a bad T-con? Is that correct?
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Old 07-10-2017, 05:16 PM   #4
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Default Re: LG 55UF6450-UA with white screen

Quote:
Originally Posted by dskall View Post
Check on both sides of t-con board fuse for voltage
If this is the fuse I have circled in red then when I tested on each side I am getting 13.22V.
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Old 07-10-2017, 05:35 PM   #5
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Default Re: LG 55UF6450-UA with white screen

T-con on the bottom of the TV, you may have liquid damage to the panel, hope not.
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Old 07-10-2017, 05:50 PM   #6
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Default Re: LG 55UF6450-UA with white screen

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Originally Posted by cliff_hootarski View Post
T-con on the bottom of the TV, you may have liquid damage to the panel, hope not.
How would I tell if there's water damage on the panel?
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Old 07-10-2017, 06:35 PM   #7
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Default Re: LG 55UF6450-UA with white screen

I would check voltages on t-con

T-con voltages (typical)
1. Vin (Vcc): 12Vdc or 5Vdc
2. (Vlogic,LCM, Vddd,VCC): 3.3Vdc
3. Vda (Vs, Vsource,VDD, Vdda,Avdd): 14Vdc~20Vdc
4. Vgh (Vgon,VGHR, Von, Vddg): 20Vdc~30Vdc
5. Vgl (Vgoff,VST,VGHF,VGHEVEN, Voff,Veeg): -5Vdc~-7Vdc
6. HVDD about 8v
7. DVDD,VDDC 3.3v, 1.2v
8. VCOM about 28v
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Old 07-10-2017, 06:40 PM   #8
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Default Re: LG 55UF6450-UA with white screen

Panel dis-assembly. People spray screen cleaner or children spill liquids and they drain down to the tab bonds and eventually eat away the copper tracks that attach to the LCD panel.

If a replacement T-con is cheap enough and the seller has a rather liberal return policy, I would try to replace the T-con before panel tear down.
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Old 07-11-2017, 01:28 AM   #9
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Default Re: LG 55UF6450-UA with white screen

Quote:
Originally Posted by dskall View Post
I would check voltages on t-con

T-con voltages (typical)
1. Vin (Vcc): 12Vdc or 5Vdc.
(13.22)

2. (Vlogic,LCM, Vddd,VCC): 3.3Vdc
(3.3)

3. Vda (Vs, Vsource,VDD, Vdda,Avdd): 14Vdc~20Vdc
(16.61)

4. Vgh (Vgon,VGHR, Von, Vddg): 20Vdc~30Vdc
(27.9)

5. Vgl (Vgoff,VST,VGHF,VGHEVEN, Voff,Veeg): -5Vdc~-7Vdc.
(Flashing between -7 & 27)

6. HVDD about 8v.
(8.09)

7. DVDD,VDDC 3.3v, 1.2v
(can't find...)

8. VCOM about 28v
(5.5, says VCOM1)
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Old 07-11-2017, 02:21 AM   #10
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Default Re: LG 55UF6450-UA with white screen

in my notes, i have vcom listed as half of avdd approx.

perhaps someone can clarify this one.
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Old 07-11-2017, 10:16 AM   #11
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Default Re: LG 55UF6450-UA with white screen

VGL should be steady. Researched vcom should be around 5.5v. Still learning

Last edited by dskall; 07-11-2017 at 10:30 AM..
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Old 07-11-2017, 01:50 PM   #12
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Default Re: LG 55UF6450-UA with white screen

Run test patterns on the TCON.
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Old 07-11-2017, 01:52 PM   #13
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Default Re: LG 55UF6450-UA with white screen

Vgl isn't steady, your readings are normal.
I suspect bad mainboard as these UF models are breaking down all over the place and it's always the mainboard.

Test patterns will confirm.
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Old 07-11-2017, 03:10 PM   #14
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Default Re: LG 55UF6450-UA with white screen

Quote:
Originally Posted by Hamie View Post
Run test patterns on the TCON.
How do I run test patterns on the T-con? I am not sure what that means.
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Old 07-11-2017, 04:03 PM   #15
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Default Re: LG 55UF6450-UA with white screen

Disconnect the lvds cable.

Connect a wire from 12v on the power supply and solder it to the TCON fuse.

Finally solder a small piece of wire to the vdc test point and connect it to pin 44 on the TCON input.

Turn on the tv.
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Old 07-12-2017, 01:44 AM   #16
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Default Re: LG 55UF6450-UA with white screen

Quote:
Originally Posted by Hamie View Post
Disconnect the lvds cable.

Connect a wire from 12v on the power supply and solder it to the TCON fuse.

Finally solder a small piece of wire to the vdc test point and connect it to pin 44 on the TCON input.

Turn on the tv.
Okay, a few questions for clarification before i do this.

1) Is the lvds cable the input cable that comes into the topside of the TCON board?

2) I can't find a DC 12V+ source on the power board... Where should I be able to find this at?

3) Last, where is the VDC test point, n the TCON? I can't find it. Also I can't find a pin 44 on the TCON? Any help on location of these would be greatly appreciated.
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Old 07-12-2017, 10:49 AM   #17
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Default Re: LG 55UF6450-UA with white screen

This may help: http://www.lcdrepairguide.com/screen...28/LG-TCON.pdf
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Old 07-13-2017, 01:53 AM   #18
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Default Re: LG 55UF6450-UA with white screen

Quote:
Originally Posted by dskall View Post
Thanks for that reference! That is a mighty tough solder job! After I did that and turned it on it flashed: Black, White, Red, Green Blue.

Does this mean bad Main Board?
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Old 07-13-2017, 03:43 AM   #19
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Default Re: LG 55UF6450-UA with white screen

It certainly looks like it must be a main board problem. The above test eliminates any panel or Tcon fault since the pictures look good.
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Old 07-13-2017, 10:27 AM   #20
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Default Re: LG 55UF6450-UA with white screen

So my question. Does this just work for LG? Some or all LG t-con?
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