LG 42LK520 Stuck on LG Logo screen even without TCON?

[jason123]

Hi Folks,
Just picked up this TV and the symptoms are non-responsive. It turns on, you can see the LG logo, when you click the menu button, you can tell that the upper left corner is changing but the LOGO overlay is on the screen.
The weirdest thing ever is if I power it up with the 2 ribbon cables form TCON to Panel disconnected the LOGO is still visible / DIM. It's like the logo is stuck on the panel (in color so not burnt in)

When I disconnect one of the ribbon cables, one side goes black and the other side has logo but the upper strip is white just like when you activate a menu. When I disconnect the other ribbon cable, the other side goes white but logo overlay is still on that side! very odd!

Labeled voltages seem to check out.
20 V and 3.5 from power board to Main card are at 20.32 V and 3.38 V
12 V to TCON is 12.03V
I see various voltages on the boards - not labeled so I don't know variance over nominal

[ducky29]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

Maybe you might have severe screen burn in.

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

I considered that, but the logo goes away on one half when you disconnect both ribbons. See photo ...other thoughts?

[petehall347]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

which cables are you disconnecting ? out or in ?

[R_J]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

Looks like he is disconnecting the lvds cables not the cable between t-con and panel.

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

Cables from TCON to panel [out]

[petehall347]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

most odd .. seems like that panel has a memory of some sort .

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

I am perplexed also...i would like to part it out and sell the main board tcon and power .. but i want to make sure they're not defective

[petehall347]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

to be sure remove all cables from t con and try again

[budm]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

So all you have is backlights, no active circuit connected to the LCD panel so all the pixels are dead but yet you can see color image on the screen, makes mo sense to me.

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

You're seeing what i am seeing...i have no clue what's going on. I am open to suggestions and and tests... i just want to make sure i don't sell bad parts

[petehall347]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

reverse engineer the panel i say .. i dont have the knowledge for that by the way as just learning

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

Update... accidentally touched the tcon and picture on screen updated. Repeated touching in that area seems to get it going temporarily suggesting TCON problem?

[Diah]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

at yours first post photo the T-CON was unprotected with Metal shield. this mean allot, at this point there are some damage at LCD where no discharge from LCD .
1- did the TV go to standby mode ? if yes
2 send command IN STOP to discharge eeprom and whole set to factory condition.
i posted over here apk on android can do this job within any mobile had IR sender.

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

I got rid of my last android S6 with ir
The tcon has a metal shield...i took ot off for the photo and to measure voltages

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

replaced the TCON board and the TV is working great. Thank you all for the help!

[jason123]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

A bit pre-mature celebration. So TCON seems to have fixed the issue. I watched one full movie, and it was great. This morning, went to turn it on, and the same problem as before. Logo screen overlay is stuck on the screen. Help!

[maxvalutech]

Re: LG 42LK520 Stuck on LG Logo screen even without TCON?

I'm no expert but doesn't tcon have an erase circuit and as its only the logo that doesn't erase then it would seem the that the ic on which that logo is stored isn't switching off its transmission once displayed at start. The model I'm working on now shows logo at switch on for a few seconds it then goes off as do backlights I think then they switch on again with TV going and menus etc available. If this is usual for LG sets it indicates two separate processes take place. The set I'm working on does have backlight problems.