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Old 04-30-2018, 08:47 PM   #1
thuss
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Default 55ub850v no picture

Hi

I could do with some advice.

Ive got a 55ub850v tv which turns and stays on, with backlights and sound but no picture.

The fuse on the the tcon has 11.78v on both sides.

There is also voltages on I assume test points at the bottom right hand corner of the tcon. There is also voltage present on the bottom left corner which fluctuate.

I have checked the (as much as I can) the components on the screen boards. They seem fine.

The psu output voltages are fine. The chips on the tcon is not very warm- whilst the main chip on the main board is hot-ish.

I was wondering if anyone could advise on what to check next or what they suspect is faulty?

I was going to change the main board.

Thanks in advance
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Old 04-30-2018, 09:43 PM   #2
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Default Re: 55ub850v no picture

What do you get on the screen if you have only one ribbon cable connected one at a time between T-CON and the tab boding board?
BTW, pictures are too out of focus to see Voltage test points on that T-CON board.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809

Last edited by budm; 04-30-2018 at 09:45 PM..
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Old 05-01-2018, 04:22 AM   #3
thuss
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Default Re: 55ub850v no picture

If I remove the one ribbon or both of them the screen still remains blank - I hope the attached photo of the voltages for the test points on the tcon (bottom right hand corner).

If I remember correctly they read between 1.2v to 13.9 and were static but not 18v.

There are no voltages written on the bottom left hand corner of the tcon.

When I removed the two ribbon cables from the tcon the voltages read the same.

Sorry really struggled to get clear focused photos
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Last edited by thuss; 05-01-2018 at 04:25 AM..
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Old 05-01-2018, 04:30 AM   #4
thuss
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Default Re: 55ub850v no picture

Bottom Left hand side of tcon
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Old 05-01-2018, 05:28 AM   #5
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Default Re: 55ub850v no picture

Check the LVDS with an oscilloscope. See if the main board puts anything out. Also check to see if the panel is getting any power.
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Old 05-01-2018, 05:15 PM   #6
thuss
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Default Re: 55ub850v no picture

no havent got a scope - the main board is getting power and then in return feeds power to the tcon hence the 11.8 v on the fuses.

Would the next step be to remove the Lvds and supply 12v to tcon fuse and connect vcc to pin 41?

Last edited by thuss; 05-01-2018 at 06:00 PM..
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Old 05-01-2018, 10:25 PM   #7
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Default Re: 55ub850v no picture

https://www.badcaps.net/forum/attach...3&d=1525142506
https://www.badcaps.net/forum/attach...0&d=1525170610
I still cannot see much test points on that inverter board, I cannot read the P/N on the barcode sticker and the P/N as printed on the board.
BTW, what brand is this 55ub850v?

Last edited by budm; 05-01-2018 at 10:27 PM..
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Old 05-02-2018, 09:20 AM   #8
thuss
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Default Re: 55ub850v no picture

its a lg tv and please see attached photo where I tested the voltages on the tcon

The part number is also on the photo
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Old 05-02-2018, 09:29 AM   #9
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Default Re: 55ub850v no picture

as far as I can make out the p/n 6807-0502c thats all there is on the board there is no additional stickers.

The second part number maybe 6871E - 3703M?

I assumed they were test points
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Last edited by thuss; 05-02-2018 at 09:39 AM..
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Old 05-02-2018, 09:38 AM   #10
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Default Re: 55ub850v no picture

LG 6871L-3703M (6870C-0502C) T-Con Board.
There many power supplies Voltages that need to be tested.
Pictures provided by shopjimmy.
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Old 05-02-2018, 10:03 AM   #11
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Default Re: 55ub850v no picture

Thank you for that - would they range from say 1v up to a max of 24V?
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Old 05-02-2018, 10:40 AM   #12
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Default Re: 55ub850v no picture

Quote:
Originally Posted by thuss View Post
Thank you for that - would they range from say 1v up to a max of 24V?
Voltage range of what test points?
Just report Voltages of all those test points, make sure to put down the name and follow by the Voltage reading.

Last edited by budm; 05-02-2018 at 10:41 AM..
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Old 05-02-2018, 06:03 PM   #13
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Default Re: 55ub850v no picture

will do thanks
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Old 05-02-2018, 06:19 PM   #14
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Default Re: 55ub850v no picture

Had two of this model both with the issues you describe in the last couple of months both were caused by faulty main boards. In both instances a replacement main board resolved the problem.Also from what I remember the 49" board will also work with no adjustments.
Hope this helps.
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Old 05-16-2018, 07:19 PM   #15
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Default Re: 55ub850v no picture

Hi

Sorry about the late response. The readings on the tcon were as follows

v18-1.6mv
v15-1.9mv
v14-1.7
v12-1.6
v10-1.6
v9-13.4
v7-13.5
v5-13.5
v4-13.7
v1-13.7mv
vdd- 1.74v
vcourfb- 1.7
vcc18- 1.6
vglI- 18.3
VIN- 11.78v
VGH - 1.5mv
VDD - 0.7
VCOM2- 22mv
VCOM1- 22mv
VCORE- 1.5mv
VGH_R- 1.4mv
VGH_even- 5.8mv
VGH_ ODD- 5.7mv


I think its the screen but any advice would be appreciated. I changed the main board still has the same symptoms. i.e No picture (the replacement board was out of a broken 49ub850v screen tv with a display).
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Old 05-16-2018, 07:21 PM   #16
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Default Re: 55ub850v no picture

I also swapped my main board (from 55ub850v) into the broken screen 49ub850v turns on and displays a broken picture.

I also swapped the tcon out of the broken screen 49yb850v into the 55ub850v but still no picture
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Old 05-16-2018, 08:46 PM   #17
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Default Re: 55ub850v no picture

Quote:
Originally Posted by thuss View Post
I also swapped my main board (from 55ub850v) into the broken screen 49ub850v turns on and displays a broken picture.

I also swapped the tcon out of the broken screen 49yb850v into the 55ub850v but still no picture
Guess it's possible that the tcon from the 49 isn't a match for the 55?

Last edited by nomoresonys; 05-16-2018 at 08:48 PM..
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Old 05-16-2018, 08:52 PM   #18
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Default Re: 55ub850v no picture

One thing to try, put the 49 tcon back in the broken screen and see if it still has the picture, a lot of times a bad panel will kill a tcon. Did you try the tcon from 55 into 49?
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Old 05-16-2018, 10:54 PM   #19
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Default Re: 55ub850v no picture

Quote:
Originally Posted by thuss View Post
Hi

Sorry about the late response. The readings on the tcon were as follows

v18-1.6mv
v15-1.9mv
v14-1.7
v12-1.6
v10-1.6
v9-13.4
v7-13.5
v5-13.5
v4-13.7
v1-13.7mv
vdd- 1.74v
vcourfb- 1.7
vcc18- 1.6
vglI- 18.3
VIN- 11.78v
VGH - 1.5mv
VDD - 0.7
VCOM2- 22mv
VCOM1- 22mv
VCORE- 1.5mv
VGH_R- 1.4mv
VGH_even- 5.8mv
VGH_ ODD- 5.7mv


I think its the screen but any advice would be appreciated. I changed the main board still has the same symptoms. i.e No picture (the replacement board was out of a broken 49ub850v screen tv with a display).
T-CON board is dead, it has 12V feeding it but lots of Voltages are really really low. Do you get the same readings if the cables between T-CON and LCD panel are removed. The board may not be compatible with your screen, also can be bad panel that causes lots of Voltages on T-CON to be low.
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Old 05-17-2018, 05:51 AM   #20
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Default Re: 55ub850v no picture

Quote:
Originally Posted by budm View Post
T-CON board is dead, it has 12V feeding it but lots of Voltages are really really low. Do you get the same readings if the cables between T-CON and LCD panel are removed. The board may not be compatible with your screen, also can be bad panel that causes lots of Voltages on T-CON to be low.
+10 Bad panel sorry to say. With 12V supply coming in and getting only mV on several of those test points, it would appear that either the T-CON is not working as previously stated or the Panel. I suspect the Panel though.
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