Working backlight and sound, but no picture (55LA6208)

[Carlozzz]

Hi,

I have a problem with my 55LA6208 LG led tv. When I turn on the tv, I only see a black screen. The black screen is powered by the leds in the background, so the back lightning is working fine.
The problem is that I don't see any pictures on the screen.

I think the fault wil be in the mainboard or the T-con board. I already measured the fuse on the T-con board, the fuse is just working fine.

So I have a tv with sound and a black screen powered by leds.

Is there anybody who knows what my problem could be?

[johns1mj]

Re: Working backlight and sound, but no picture (55LA6208)

Please include pictures of the back of the tv including input and t-con.

First double check connections. You can try disconnecting one ribbon at a time to see if half a picture shows up.

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

Please include pictures of the back of the tv including input and t-con.

First double check connections. You can try disconnecting one ribbon at a time to see if half a picture shows up.

There are two flat cables on the T-con board going to the screen, i disconnected one ribbon at a time, but it did not change anything, it is still a black screen with led lighting behind it.

Here are some pictures of the back of the tv:

[budm]

Re: Working backlight and sound, but no picture (55LA6208)

"I already measured the fuse on the T-con board, the fuse is just working fine." working fine? Do you mean it shows <1 Ohm of resistance?
So did you check to find out if you have 12VDC at both ends of the SMD fuse on the T-CON board with ref to the chassis GND?

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

Yes, there is 12VDC at both ends of the SMD fuse with ref to the chassis GND.

[Andrew F. Ali]

Re: Working backlight and sound, but no picture (55LA6208)

Let's see what we have:
1. BL-ON working as Backlights are ON
2. PS-ON working as TV is Powering ON
3. Audio working as TV sound can be heard
4. T-CON Bd Supply 12Vdc is good as 12Vdc is seen on both sides of Fuse

What input are you using?
Is this happening on ALL inputs?

OK then try cleaning and re-seating the Flat cable between the Main Bd and the T-CON Bd....Wipe the gold fingers on both ends with Isopropyl alcohol.

If that doesn't work then your Main Bd needs fixing/replacing

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

Thanks for the feedback!
I got this problem on all my inputs, if the problem was only on one input, I would have seen some pictures or input message when I changed channels. I tried cleaning the flat cable between mainboard and T-con board, but it did not make any difference.

Can I test something else to make sure my problem is in the mainboard and not the T-con board?

[Andrew F. Ali]

Re: Working backlight and sound, but no picture (55LA6208)

Yes you can check these voltages on the T-CON Bd.
Measure and report these voltages:
1. VGH (V0n) 20~30Vdc Gate ON supply
2. VGL (Voff) -5~-8Vdc Gate OFF Supply
3. VDD (Vlogic) 1.8~3.3Vdc Supply Logic Input (especially this one)
4. VDA (AVdd) 13~20Vdc Gamma Supply voltage

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

I got these voltages:

VGH: 0Vdc
VGL: -6.94Vdc
VDD: 0.5Vdc
And I could not find the VDA

I hope you know what the problem is.
Thanks in advance!

[Hamie]

Re: Working backlight and sound, but no picture (55LA6208)

Well with voltages like that you have a faulty TCON.

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

I changed the t-con board, but there is still no picture on the screen. The voltages I measured are the same as on the old t-con board.
Is there anybody who knows what my problem could be?

[dick_barton]

Re: Working backlight and sound, but no picture (55LA6208)

Disconnect the 2 panel cables from the Tcon and measure those voltages again.

Fault finding at a distance without the set in front of you is difficult at the best of times and you have had several helpful suggestions hopefully leading to narrowing down the fault.

[Carlozzz]

Re: Working backlight and sound, but no picture (55LA6208)

Thanks!

Measured it again without the cables connected:

VGH: 27,9Vdc
VGL: -6.9Vdc
VDD: 16.8Vdc

[Diah]

Re: Working backlight and sound, but no picture (55LA6208)

did you used before this fault your mobile screen mirroring with your LA6208?

in case you did or not, now you have LVDS com signal has being changed., this happen too if some one play with hidden menu EZ_Adjust.

try first to reset it to factory state by using (Smart Remote apk )at mobile android such galagxy S5 or any one had IR sender. the function button at this program called ( In_Stop ) one time press then with yours TV RC put 0413 the TV will go to stand by.. leave it one minute then start it again. hope your screen come back

[budm]

Re: Working backlight and sound, but no picture (55LA6208)

Thanks!

Measured it again without the cables connected:

VGH: 27,9Vdc
VGL: -6.9Vdc
VDD: 16.8Vdc

It sounds like you LCD panel is loading down your VGH supply when you gave the ribbon cables between the T-CON and the LCD panel connected.
Example of how VGx are generated and what they are for.
https://cdn.badcaps-static.com/pdfs/...b317805c9b.pdf
https://cdn.badcaps-static.com/pdfs/...6c316493a3.pdf

[Diah]

Re: Working backlight and sound, but no picture (55LA6208)

this is LG IPS Panel. had different feeds as usual. they shared this tech only with Sony. . there are no drops.

[dick_barton]

Re: Working backlight and sound, but no picture (55LA6208)

It sounds like you LCD panel is loading down your VGH supply when you gave the ribbon cables between the T-CON and the LCD panel connected.
Example of how VGx are generated and what they are for.
https://cdn.badcaps-static.com/pdfs/...b317805c9b.pdf
https://cdn.badcaps-static.com/pdfs/...6c316493a3.pdf

+1 Does appear to be some sort of loading on the Tcon supplies and I would be suspecting a possible panel fault.

[dick_barton]

Re: Working backlight and sound, but no picture (55LA6208)

this is LG IPS Panel. had different feeds as usual. they shared this tech only with Sony. . there are no drops.

Hello Diah,
Can you explain a little more what you think the problem may be regarding IPS panel.

[Alastair E]

Re: Working backlight and sound, but no picture (55LA6208)

Expect the panel itself. LG make utter shit panels!

[Diah]

Re: Working backlight and sound, but no picture (55LA6208)

Hello Diah,
Can you explain a little more what you think the problem may be regarding IPS panel.

hello Paul

over years till now, never found IPS Panel from LG get any operation Fault unless faced visibility damage by human.

the method where you use over this forum disconnect T-CON ribbon to Panel wouldn't work , because the feed are absolute different. its mean one half will be white but when you disconnected the other one only both side will be black,

there are no problem with panel.. as i said if it not had damage on right side down when you facing the panel