LG 55UF6450 No Backlights

[eagle00799]

I have this tv that i'm trying to fix for a family member, LG 55UF6450 Ultra HD 4K LED tv. They said the picture went out but it still had sound, they no longer have the original remote so I have no remote to work with.
This is what I have so far.
I can not see any image on screen using flashlight.
i'm not sure of what input it is on and can not see menu to change the input but have tried all HDMI inputs but it made no difference so no image and no sound so far.
When powered on the red light on bottom front of tv blinks 2-3 times and lights on main board come on but no flash at all of backlights.
Voltages I have checked are as follows.
Main Cap is 160v-off/400v-on
t-con fuse reads 13.2v-on
Led+ is 129v on both positives when powered on and 62v when off.
Voltages on the connector when powered on are as follows.
PWR-On=3.3v
GND
13.3v
13.3v
GND
DVR-ON=3.4v
P-DIM1=0
GND
13.2v
13.2v
13.2v
P-DIM2=0
Not sure of which one of these controls the BL_ON.
Any idea's would be appreciated.

[R_J]

Re: LG 55UF6450 No Backlights

What is the voltage in the led- pins when on?
Do you see a quick flash of the led backlight at all

Put your model number into the search, there are a few other threads on this model
Like this one: https://www.badcaps.net/forum/showth...light=55UF6450

[Andrew F. Ali]

Re: LG 55UF6450 No Backlights

The DRV-ON pin would be the one to turn on the Backlights. If you say you have on both +ve pins to the backlights but does it remain at that voltage or does it go down to a lower voltage and did you measure the -ve backlight pins WRT chassis GND, if so what did you get? From what I read so far it would seem you have a bad backlights issue but we need more info to correctly guide you.

[eagle00799]

Re: LG 55UF6450 No Backlights

Hi RJ thanks for the reply, I get 8.6v and 6.7v on the 2 negative posts and I get no flash of backlights at all.

[eagle00799]

Re: LG 55UF6450 No Backlights

Hi Andrew thanks for your reply also, the 129v holds steady on both + posts and I get a 8.6v and 6.7v on the 2 negative- posts

[eagle00799]

Re: LG 55UF6450 No Backlights

So if I am getting voltage from the negative posts I assume it's shorted backlights?

[R_J]

Re: LG 55UF6450 No Backlights

Are you sure the backlights are not on? 129v - 8v = about 120 volts to the led's.
When you did the flashlight test did you have a source connected and did you have audio?

[eagle00799]

Re: LG 55UF6450 No Backlights

I had a dvd player connected to the HDMI but could not see or hear anything. I have no remote and can not see the menu to switch input.

[eagle00799]

Re: LG 55UF6450 No Backlights

The LG has 1 button on the bottom that controls everything so it's hard if not impossible to know how to get it to the right input.

[Diah]

Re: LG 55UF6450 No Backlights

if the back light voltage as you wrote show 129V. the LED should be light on when tv turn on and this you can easy to see them. if voltage there but thy are out then you have broken ( CUT OUT ) Led one or more.. but in this case with flash light you can see some things on the screen, look close at turn on in the middle of the screen or the top left.

[R_J]

Re: LG 55UF6450 No Backlights

connect the dvd to hdmi with dvd power off then turn tv on, then turn on the dvd, sometimes the tv will find it.
I guess you could try disconnecting one of the ribbons between the t-con and panel and see if you get anything on half the screen.

[Andrew F. Ali]

Re: LG 55UF6450 No Backlights

I agree with the other Learned Techs that are replying to your issue. Turn the TV on and look at the back of the TV. You should see through the holes if the Backlights come on or not Then with the TV on measure the voltage on the two ends of the T-CON Bd. fuse to see if there is any power to the T-CON Bd.

[eagle00799]

Re: LG 55UF6450 No Backlights

Ok I lucked out a bit, the remote for my LG DVD player works on the tv so I was able to switch inputs and now I have sound but still can not see any image. I disconnected each side of the t-con 0ne at a time and the side I disconnect will get a very quick and dim flash of light when powered on. I have 13.2 volts to both ends of the fuse on the t-con bd.

[eagle00799]

Re: LG 55UF6450 No Backlights

Pic of t-con bd, fuse F1 13.2 volts to both sides

[R_J]

Re: LG 55UF6450 No Backlights

This is where you take out your scope and check the signal on the lvds cable, without it the problem could be with the main board or t-con, I suspect main board myself.
If you disconnect the small white plug from the t-con do you get brighter backlights?

[eagle00799]

Re: LG 55UF6450 No Backlights

When I unplug the small white plug the lights come on full screen.

[R_J]

Re: LG 55UF6450 No Backlights

Ok, so your backlights are ok, and the power supply is ok, others have had problems with the mainboard. Shopjimmy had all 3 boards for under $90.00 but are out of stock.

[eagle00799]

Re: LG 55UF6450 No Backlights

Thanks for your help guys, I will see if I can find a main board. I have done some browsing and have seen many different boards for the LG 55UF6450, curious if any of those will work if I can't find the exact board that's in this tv.

[Andrew F. Ali]

Re: LG 55UF6450 No Backlights

The EAX- - - - - part number on the Main Bd. MUST match for the TV to work. Other boards that look similar but do not carry the same part No. would be outfitted with different software that will not math the T-CON Bd.

[Diah]

Re: LG 55UF6450 No Backlights

hmmm. most always tinny small boards from LG need heating later , as they used at manufacturing halogen free since 2015.

use hot air or backing offen ( with out air fellow ) to rebel the main board .. or just the reheat the main processor