LG 65UK6090PUA - picture dark

[Danstona]

Was watching this set, and suddenly it went dark. Picture is still visible, just very dark. Tried checking all settings, adjusting brightness to 100% no change. Reset through menus, no change.
bought used boards from ebay (power and input boards) replaced with same results, changing brightness does seem to have a slight affect.. but not to normal visibility of picture.
I'm handy, fixed TVs before.. I can't see any issues with boards... hoping someone can point me in the right direction to properly diagnose. I don't believe the LEDs are caput, since the picture is on and equal across screen for visibility... just too dark.
thanks

[nomoresonys]

Pictures of each board and one including all the boards.

[nomoresonys]

We no longer help people who do not post pictures... maybe that's just me.

[Danstona]

replacement power board

[Danstona]

original power board

[Danstona]

original input board

[Danstona]

replacement input board

[Storyteller12]

My guess is backlights. Especially if you replaced both boards and same symptom. But you need a multimeter and led tester to test the backlights.

[Danstona]

Well I have good multimeter.. I would need to know what the led tester is... with the back off, they light up... I just feel like they should either work or not... not be half bright but still be defective.

[nomoresonys]

So you're saying when you turn tv on you can see the backlights are on, can you very carefully check the dc voltage of looks like C611 the 460 volt capacitor put a probe on each lead, use CAUTION it could be about 400 volts, so watch where you put your hands, you don't want that going thru you, don't do if you're uncomfortable with this kind of testing.

[nomoresonys]

Something to try, heat up looks like C205 500 volt capacitor for a minute or so with a hairdryer, try tv, see if there's any change, don't wait til it cools down, try it while it's still hot.

[nomoresonys]

Since things acted the same, maybe keep original mainboard in for testing.

[Danstona]

Sorry for such a long time since testing. I still have the set in basement for repairing, I just had some issues preventing me from doing the tests.
I checked voltage on the c611 460v cap and it has 21.7v on each lead to a grounding screw.
I tried heating up c205 as suggested and if any change, it was the tv not starting immediately, but no chance in picture at all.

[EazyBone]

Long time.. lol anyway, still backlights should be tested. Using a tester. Amazon $15

[Davi.p]

Hi, sorry i do not understand well if the light from the back could he considered ok or not. Anyway my two checks: is there a light sensor on a separate small pcb watching the room? Have you opened the panel leds pool and saw how the bars are made? Some Samsung bars comprises opto diodes in a series, for light measuring, the series could be broken.. bye..

[Danstona]

See photos, both are taken in darkened room

[EazyBone]

Is the photo of the screen showing the defect of being dark? Am I missing something it looks fine. Can you circle whatever it is.

[Danstona]

This is the image, this is from a completely black room. The picture is very "dim" it's there, but it's as if the backlights aren't firing fully. This is why I don't think it's the backlights that are the issue, they all work, but the whole screen is very dark.
I can test them if you explain the process, I purchased the tester now.

[KYBOSH]

Its likely your backlights. When they fail they usually very noticeable (whole sections of the strip are out) but its possible that failing LEDs with higher resistances can drop the overall brightness of a number of strips. This TV set us about 6 years old so a replacement of the LED lightstrip wouldnt be a bad idea (~$50US on shopjimmy) if you intend on keeping it for the long haul. The chances of the PSU doing this (without throwing an error) is almost non-existent.
Good Luck!

Also be sure to send a video feed to the TV to gauge its proper brightness. The menu/screensaver screens are programmed to have pretty light brightness settings. If you want to show an example then install a FireTv doggle on it, crank the brightness up and then show us what you are seeing.

[Davi.p]

The chances of the PSU doing this (without throwing an error) is almost non-existent. Good Luck!

You let me think also to another possible issue, that is... right the power supply! The backlight controller ic sometimes fails alone, also in such a way..