LG 55" Curved Model 55UG870T - No picture

[angelos]

Hi Guys,
I got in this set that has no image but the back lights are running. I tested all the usual issues relating to panel faults and there were none. On the TCON, the two LVDS cables were unplugged coming from the main board and then when i started the TV i got the burn in mode (green, blue red , white etc cycling). This tells me that the panel is ok. The only thing i am not 100% sure of is that i dont know if my TCON, head end is being processed. But i doubt its that. The LVDS cable looks clean. No water damage in TV and not much dust.
I measured all the power supply voltages and they were spot on.
The only thing remaining is the main board. I know LG have issues with the processor balls (BGA) going dry joint but what i want to know is how to be 100% sure that the fault is the main board and not something else.
When plugging in HDMI1 i do get audio from the movie i am playing so that part is ok.
I added some photos to jog your minds if you now the set and its common faults.
I had to drop the resolution of the photos because it would not upload.

Kind regards
A Anagnostou

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Did you try an update?

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Nope. I have never asked LG for support. I will try it. Over the courier of next week I will try find out who can supply me the firmware.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Hi Nomoresonys,
I just found the LG site that can supply me with the software update. If you look at the procedure. It prompts you to make a choice so now I am in the blind. I can't see what is happening. The procedure does not say if you must have the tv unplugged and then insert usb stick into the tv. I am going to post some screen shots of the "How to upgrade" file.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Sorry, I used my cell phone to screen grab the manual. How would I go about doing the firmware update in the blind?

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Did you try a simple reset, unplug tv for 5 minutes, hold power button on tv in for 30 seconds, then plug it back in and try it.

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Another thing to try is to simultaneously hit the power key and the volume down key, then unplug your television for a while.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Are these the standard reset procedures specifically for LG? I will try it later today.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

I was told by a colleague that if you have a blank screen but look at the screen at an oblique angle and you see a purplish hue then that means the panel is good but we are not getting any video. So that would mean the video processor is faulty on the main board. The cost of the main board is 41% of the cost of a new tv. Nice Hey, What a waste. To the rubbish bin.

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Need to check the tcon, check vgh, vgl etc, there's probably 100 videos on youtube for fully checking tcons.

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

If the tcon readings are not what they should be, unhook tcon ribbons going to panel on tcon side and retest.

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

When you lightly touch/tap the screen you get light flashes correct?

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Sometimes one of the little mlc caps responsible for vgh will go bad on tcon, resulting in no picture.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Need to check the tcon, check vgh, vgl etc, there's probably 100 videos on youtube for fully checking tcons.

All the Voltages are correct.
VGH = 28V
VGL = -6V
AVDD = 17V
HAVDD = 8.5V

Remember that i said i one of my previous posts that when i unplugged the LVDS cables but left in the other two cables (refer to photo tcon.jpg) and i started up the tv like that. The LED panel started showing, Green, blue, red, white, black and repeated it indefinately. This is ageing mode. This tells me the panel and its voltages are fine.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

When you lightly touch/tap the screen you get light flashes correct?

Absolutely backlights are running.

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

This is a tough one but it does seem fixable, had the aging mode on my old sony and an update fixed it, but that tv didn't need any remote commands to update, I just put in usb and turn it on, wonder if there's some kind of auto-run update for this type of situation?

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

All the Voltages are correct.
VGH = 28V
VGL = -6V
AVDD = 17V
HAVDD = 8.5V

Remember that i said i one of my previous posts that when i unplugged the LVDS cables but left in the other two cables (refer to photo tcon.jpg) and i started up the tv like that. The LED panel started showing, Green, blue, red, white, black and repeated it indefinately. This is ageing mode. This tells me the panel and its voltages are fine.

Wouldn't this mean theres a problem in the panel, ribbon cable or one of the panel driver/address boards?

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

Wonder if tape cut-off method would work.

[angelos]

Re: LG 55" Curved Model 55UG870T - No picture

Wonder if tape cut-off method would work.

I tried that and it made no difference. When you have a short in the panel and "tape off" the guilty circuit then your DC to DC IC starts to generate the VGH, VGL... voltages and that's why you get a picture. My panel voltages are always present.
When putting the panel into ageing mode and i get the tv to cycle red, green blue etc.. then i inspect the image. There is no line, blemish or darkened spot visible on the panel. I have a pure uniform image telling me the panel is fine. What do you think?

[nomoresonys]

Re: LG 55" Curved Model 55UG870T - No picture

And your sure the ribbon cables to panel are all good, clean, undamaged.