LG 55ub830v - Back Light, Sound but no picture

[reeso3000]

Hi Guys!

I was given an LG 55uf850V by a friend who was told by LG that the panel had failed and would cost far too much to replace (All diagnosed over the phone). Can they really diagnose this so confidently over the phone?

Anyway I took the back off etc and after some googling thought I would swap the tcon due to it's low cost and easy replacement - It arrived yesterday and it made no difference (also replaced the ribbons as the second board came with some).

I have read a thread on here about a similar model tv (55ub850v) and it has a very similar looking tcon board so I tested the voltages I could match up that were suggested in the thread (A few test points were not present as far as I could see) and my findings are as follows:-

v18 0.41v
v14 3.95v
v 10 7.8v
v9 8.45v
v5 12.2v
v1 15.8v
vd0 16.7v
vcore 1.2v
vcourfb 5.76v
vcc18 1.82v
vgl1 negative 5v
vin 11.92v
vgh odd 28v/negative 5v
vgh even 28v/ negative 5v
vcom1 5.8v
vcom 2 5.9v

Just to note the vgh odd and even switch back and forth between 28v and negative 5v no idea if that's supposed to happen?

If I unplug the left side ribbon on the tcon I get just the white light on half of the screen and black with purple lines on the other, If I unplug just the right side ribbon the whole screen remains black. I have also found moving the ribbons slightly can cause changes to the lines. Voltages remain the same if the ribbons are disconnected or connected to the tcon board.


Any help would be great!!

Thanks in advance

[yohnsee]

Re: LG 55ub830v - Back Light, Sound but no picture

Hello,
I would have done the same to test the set out. I mean, to buy a new TCon.
You may already know this from your research, sound and backlights mean working main board and psu. If after replacing the Tcon nothing has changed, then yes, your display may be faulty. They diagnosed over the phone - a reason for this could be that the service guy already knew this series of TVs, and they may have a higher rate of defective LCDs. And guess what, he was right this time.

[reeso3000]

Re: LG 55ub830v - Back Light, Sound but no picture

Hi Yohnsee,
Thanks for the reply! In the other thread someone mentioned swapping the main board resolved the issue similar to this - is it possible the part of the main board has failed so it gives off sound but no picture and if so are there any checks I can do? also if the panel has failed is there much I can do to fix it? does the fact I can get some colours by removing ribbons mean anything at all? Thanks again!