55ub850v no picture

[thuss]

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

[budm]

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.

[thuss]

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

[thuss]

Bottom Left hand side of tcon

[CapLeaker]

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.

[thuss]

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?

[budm]

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?

[thuss]

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

[thuss]

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

[budm]

LG 6871L-3703M (6870C-0502C) T-Con Board.
There many power supplies Voltages that need to be tested.
Pictures provided by shopjimmy.

[thuss]

Thank you for that - would they range from say 1v up to a max of 24V?

[budm]

Originally Posted by thuss

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.

[thuss]

will do thanks

[satinser]

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.

[thuss]

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).

[thuss]

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

[nomoresonys]

Originally Posted by thuss

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?

[nomoresonys]

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?

[budm]

Originally Posted by thuss

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.

[Andrew F. Ali]

Originally Posted by budm

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.