LG 55UJ6300 Very Dim

[dhoff024]

I am trying to diagnose my mother and father in laws TV. The TV has a picture and is functioning properly other than the screen is very dim. If you are in a bright sunny room you can't see anything but if you are in a dark room you can see the picture but you can tell it's not right. I don't know if it's an LED probably, I have had other LG's that had nothing but problems with the LED's but when those had problems the screen would be completely black. Would love some help diagnosing so I can get this fixed for them. Thanks in advance!

[neilc6]

Re: LG 55UJ6300 Very Dim

Backlight issues are 99% the backlights themselves. On LGs, the protection circuitry usually kicks in to shut down the backlights but I have seen it a few times where it doesn't. https://techhometravel.com/lg-ln-ser...ed-backlights/

[dhoff024]

Re: LG 55UJ6300 Very Dim

Backlight issues are 99% the backlights themselves. On LGs, the protection circuitry usually kicks in to shut down the backlights but I have seen it a few times where it doesn't. https://techhometravel.com/lg-ln-ser...ed-backlights/

Thank you, I suspected backlight was the problem since I have had that issue with other LG's but other would flash or just not light up this lights up but is very dim so wanted to get some opinions before I went ordering new LED's.

[R_J]

Re: LG 55UJ6300 Very Dim

Measure the voltage across the +/- on the plug going to the led's, it should be around 130vdc

[dskall]

Re: LG 55UJ6300 Very Dim

I repaired one that had 3 out of 16 strips working. And it still had a picture.

[dhoff024]

Re: LG 55UJ6300 Very Dim

Measure the voltage across the +/- on the plug going to the led's, it should be around 130vdc

I am coming up with 211 volts DC. Tested several times 211 each time.

[dhoff024]

Re: LG 55UJ6300 Very Dim

I repaired one that had 3 out of 16 strips working. And it still had a picture.

My gut tells me it's the LED's since it seems to be so common with these LG's but I have never seen one still have some backlight and a picture like all the ones i have done have had no backlight or it would flash then go out.

[R_J]

Re: LG 55UJ6300 Very Dim

I am coming up with 211 volts DC. Tested several times 211 each time.

211 volts seems high, I suspect some of the led's in the panel are bad, there is less current being drawn so the voltage goes up.
Looking at shopjimmy, there are 10 strips with 4 led's on each, 40 x 3volt =120v total
It looks like the backlight control circuit is quite simple and keeps operating if a few leds are bad, not like some circuits that will shut down if even one led is weak.

[dhoff024]

Re: LG 55UJ6300 Very Dim

211 volts seems high, I suspect some of the led's in the panel are bad, there is less current being drawn so the voltage goes up.
Looking at shopjimmy, there are 10 strips with 4 led's on each, 40 x 3volt =120v total
It looks like the backlight control circuit is quite simple and keeps operating if a few leds are bad, not like some circuits that will shut down if even one led is weak.

Ordered some LED's from shop Jimmy. Got the TV torn apart today and think I found the culprit as you can see in the photo. I will update once I get the parts and get it put back together.

[neilc6]

Re: LG 55UJ6300 Very Dim

On that model the LEDs turn blue as well. Best to replace them all with the TV apart.

[sigmeyer]

Re: LG 55UJ6300 Very Dim

Yes , i can confirm i have repaired these sets before , 99% is the backlight , if you have some parts lying around and a 10Watt 33k-ish ohm resistor you can build a simple Backlight tester to save you the time of troubleshooting elsewhere.

[dhoff024]

Re: LG 55UJ6300 Very Dim

Ok so I replaced the backlight and all was good for a day now the backlight is completely out but picture can be seen with a flashlight could the backlight really be bad again or could the be a power supply problem?

[dskall]

Re: LG 55UJ6300 Very Dim

Again you will need to measure your backlight voltages.

[neilc6]

Re: LG 55UJ6300 Very Dim

Did you replace all the strips with new or just the bad strip? Did you turn down the backlight level after the repair and check all inputs and apps?

[dhoff024]

Re: LG 55UJ6300 Very Dim

All strips were replaced with new ones from shop Jimmy. I just checked voltage and I am at 254 volts DC. I did not turn down the backlight or change anything just replaced the LED's and put it back together. Worked perfect for a day now no backlight at all.

[dskall]

Re: LG 55UJ6300 Very Dim

I assume you don't have a backlight tester. You probably have an open circuit.

[dhoff024]

Re: LG 55UJ6300 Very Dim

I found the culprit after tearing the TV back apart. Now I need to get the parts warrantied by shop jimmy.

[nomoresonys]

Re: LG 55UJ6300 Very Dim

did you test the new leds before installing them? is that burnout in the exact same place as the original fault?

[dhoff024]

Re: LG 55UJ6300 Very Dim

did you test the new leds before installing them? is that burnout in the exact same place as the original fault?

I did not test the new ones before installing. This burnout is not in the same spot.