LG 55LF6000-UB Screen goes white and bright on occasion

[dman535]

I picked up this TV and did an LED replacement. Seems to work fine - then today the screen goes white and gets all washed out.
Everything when back together fine with the exception of the Tcom board, the chassis was a little different and didn't accommodate mounting - would that cause this problem? It seems to only happen after the tv has been on for a while and is fixed by unplugging it and plugging it back in.

[budm]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I picked up this TV and did an LED replacement. Seems to work fine - then today the screen goes white and gets all washed out.
Everything when back together fine with the exception of the Tcom board, the chassis was a little different and didn't accommodate mounting - would that cause this problem? It seems to only happen after the tv has been on for a while and is fixed by unplugging it and plugging it back in.

That looks like bad GAMMA Voltage.
"Everything when back together fine with the exception of the Tcom board, the chassis was a little different and didn't accommodate mounting" What do you mean by that? Some one put something else in place?

[Diah]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

try to had reset with command ( IN_STOP ) to roll back all driver.

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

That looks like bad GAMMA Voltage.
"Everything when back together fine with the exception of the Tcom board, the chassis was a little different and didn't accommodate mounting" What do you mean by that? Some one put something else in place?

I had brand new LED strips installed in an LG 55LB5550-UY but the panel was damaged. I used that chassis to mount everything from the 55LF6000, and it fit fine - with exception of the tcom board at the center bottom. So I let the board float and secured the wires. It didn't appear that the board needed to be grounded or that there was a heat dissipation need - maybe I was wrong.

[diif]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I had exactly the same after I'd replaced a gamma IC. I forgot the thermal pad and they are sensitive to heat. Picture was ok for a while then washed out.

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I had exactly the same after I'd replaced a gamma IC. I forgot the thermal pad and they are sensitive to heat. Picture was ok for a while then washed out.

The chip I outlined in red is the gamma ic if I am not mistaken. Can I just add a heat sink to it to help dissipate the heat - I have some small ones I picked a while ago.

[diif]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I had to replace it again once the picture had gone white, it had failed again. They usually use a thick flexible thermal pad that touches the tcon shield like https://www.aliexpress.com/item/32392804900.html stacking if necessary to touch the shield

As long as it's not going to short anything whilst attached or again if it falls off I don't see why an aluminium one couldn't be used if you can't use your original shield as part of the heatsink.

You can measure the gamma voltages on the test points GM1, GM2.. to confirm it is the gamma IC that has failed.

[tvtimmy]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I would also add a ground wire from the tcon board to the chassis.

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

As I am looking over the pictures. I came to the conclusion that the 55LB5550-UY had a shield and the 55LF6000-UB did not. This picture I posted matches what this video screen shot from Shop Jimmy shows. If there is no shield than there is no provision for the silicone pad..am I mistaken?

Next steps:
Add ground wire
Check voltages at Tcon board and replace if needed.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Looks like you have the right conclusion, no shield required, one question is are the screws that hold the tcon in place also used for grounding? Is the chip too hot to touch? maybe check the tcon test points, might just be bad tcon. The tests narrow down the possibilities.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I picked up this TV and did an LED replacement. Seems to work fine - then today the screen goes white and gets all washed out.
Everything when back together fine with the exception of the Tcom board, the chassis was a little different and didn't accommodate mounting - would that cause this problem? It seems to only happen after the tv has been on for a while and is fixed by unplugging it and plugging it back in.

Do you mean unplugging power cord and replugging. If so do you do it immediately and it's cleared up even before tv cools down?

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Do you mean unplugging power cord and replugging. If so do you do it immediately and it's cleared up even before tv cools down?

I gave it maybe 2 minutes to cool down before plugging it back in.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Ok, so if it takes a while for fault to show up, maybe test those testpoints on tcon when first turned on, make note, then test them after fault shows up, see if you notice a difference on any of them. Would be nice to have a guide handy that told what each of those testpoints should read, would make troubleshooting tcons a lot easier.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Tcon here if that is the one you have, click picture to enlarge: https://www.shopjimmy.com/lg-st5461b...-con-board.htm

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

I added grounds and updated firmware on the TV. You can see the difference in the chassis to the board. Not how I usually want to do things, but thought ripping off the brand new LED strips from the old chassis would have caused more problems.

Will see if problem reappears, I did not make any attempts at this point to adapt any cooling to the IC.

[budm]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

So the two LCD panels are not the same model number, correct since the T-CON mounting holes are not the same?
May be one draws more current than the other?
I would look up the spec sheet of both panels and compare them.

[dman535]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

All the the components match from the original unit, with exception to the metal backing. Everything fit the same as the original except for the tcom board.
I had already replaced led strips on the 55lb550 and the lcd panel for damaged, so I got the 55lf600 and used all of its pieces with the 55lb550 back.

[budm]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Like I said, the panel are not the same model that is why the mounting holes for the T-con are not the same. https://www.badcaps.net/forum/attach...7&d=1565543476
You cannot use the T-CON board that was made for LCD panel that its belongs to?
What are the model number of the LCD panel? not the model number of the TV.
You can see the sticker: https://www.badcaps.net/forum/attach...4&d=1565533811
The spec sheet of the LCD panel will give you the electrical specification of the T-CON board which comes with the LCD panel.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

.

[nomoresonys]

Re: LG 55LF6000-UB Screen goes white and bright on occasion

Ok, if I understand it right, your panel is the ub, so you need a ub tcon at least, wasn't there a tcon in the other one?