LG 65UH615A - Backlight on with No Picture Black Screen

[jimmyboy111]

you press the power button and get the backlights so the mainboard must be functioning at some level .. standby 5v is normal and power supply rails are clean and normal

.. I am trying to see if I get sound by pressing changing inputs but not luck .. 12v is on the t-con and I have swapped the power and t-con board already which leaves me at the mainboard again .. the main was swapped as well and I got the same black screen no image so either it is the main or I got a board with the same problem as the original

.. guessing maybe bad flash or cpu problems on main .. if anyone has any clues send me a message

Thanks

[Diah]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

check yours lcd panel.. if you disconnect one side ribbon cable between t-CON and panel you will see half picture on one side of the panel.. also on the panel boards you have U ribbon cable can remove one on each side to have 3/4 of screen side image... all will goes to one result panel broken some where

[jimmyboy111]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

Did that .. disconnecting left and then right of t-con .. no real difference

.. panel boards? do you mean the panel driver chips on the edge of the glass? .. I havent looked at those yet .. good idea .. I had someone spill soda on a screen and screw those up before since it would run to the bottom of the screen

[jimmyboy111]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

checked the driver boards on the edge of the glass panel .. all look normal no corrosion or dirty connectors .. checked again with scope .. notice that the T-CON main processor is not running normal temp .. dead although there is clearly 12v on the main fuse and the diode input on the board
.. unplugged all the edge panel drivers and now it runs but now the mainboard does not turn on the backlight

.. connected to left alone and the t-con runs but no backlight .. connecting to right driver board and all the voltages get dragged down
.. there is only a few caps and a single ST Micro controller chip on the driver board but I cannot find any info on the SMD code .. any help would be appreciated

PHOTOS

https://imgur.com/a/1C6vFlc

[budm]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

No cables between T-CON and the Tab bonding board, then check the resistance of all the MLCC (Multi Layer Ceramic Cap) on the tab bonding boards to see if any of them show low resistance (<100 Ohms).

[diif]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

It's an I2c eeprom probably holding EDID information. You can check the voltage at the VCC pad or check the resistance between that and ground. It's more likely to be a shorted capacitor.

[jimmyboy111]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

Thanks Bud .. yes did that all showed normal no shorted ceramics .. just checked there is a short to the ground test pad on the board to pins 1 2 3 and 4 on the chip so it is toast .. turned on the board one more time and the 3.3v test pad on the driver board shows 1v but the chip doesnt seem that hot

Diif .. is EDID is unique to this specific TV or could I rip one off another broken panel?

[budm]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

Thanks Bud .. yes did that all showed normal no shorted ceramics .. just checked there is a short to the ground test pad on the board to pins 1 2 3 and 4 on the chip so it is toast .. turned on the board one more time and the 3.3v test pad on the driver board shows 1v but the chip doesnt seem that hot

Diif .. is EDID is unique to this specific TV or could I rip one off another broken panel?

But pin 1,2, 3, and 4 are connected to Ground plane as you can see the traces. What is the resistance between GND and VCC test pads?

[jimmyboy111]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

When your right your right .. kind of strange having a micro with 4 pins all connected I didn't look close enough .. pulled out a better ohmmeter with sharper probes and I found 3 shorted caps .. any suggestions on swapping caps so close to tab bonds? I guess maybe some low temp solder and a tiny iron

[nomoresonys]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

Could be only one is shorted, remove one on an end, see if it's shorted out of circuit and see if other 2 are still shorted.

[budm]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

When your right your right .. kind of strange having a micro with 4 pins all connected I didn't look close enough .. pulled out a better ohmmeter with sharper probes and I found 3 shorted caps .. any suggestions on swapping caps so close to tab bonds? I guess maybe some low temp solder and a tiny iron

Show us the pictures fo the suspected bad caps.
I use 40W wide tip soldering iron and add Lead solder to each end of the cap to remove it.

[jimmyboy111]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

You guys are on a roll today Attaboy .. I put a meter on low ohms and found the ceramic on the driver board with the lowest value removed it and the others opened up guess they were in parallel .. swapped in a ceramic cap from junk board and now it's firing up .. I was about to give up this one

.. the LG 4K tv's have bad ceramics in them I wonder how long before the next one shorts out

[budm]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

MLCC failure mode is shorts circuit or low Ohm mode, this happens to just about all brands of TV not just LG, you will see lots of threads about bad MLCC, we all have lots of experience about these failed MLCC.
BTW, if you did not use good meter and good probes then we would not have found out the cause of the problem, remote troubleshooting requires valid data, I am glad you did find good meter and probes.

[nomoresonys]

Re: LG 65UH615A - Backlight on with No Picture Black Screen

Nice save, nice big ole 65 incher too.