LG 55LS4500 Dim Bars Across Screen

[maveriik]

Hi all, when I turn the TV on, everything works fine for about 5-10 seconds, until the TV boots up and it shows what input is on. After that there is a slight flash and the bars/parts of bars appear. Sometimes only half or parts of the bar appear and then another couple seconds later the other parts appear. I don't think it's burnt out or shorted LEDs because they all seem to work perfectly at the beginning... Here's a picture. This is the worst that it gets.

There is a blinking light that blinks 4 times, pauses, and then blinks 4 times again. It is LD701. The P/S board number is EAY62512801.

Some of my voltages are pretty messed up too.

The 24v pwr on is reading 7 volts.
I read some of the led's as well, I can post exact numbers later, but I think 2 VC's on the led's were around 54V and the rest around 38V.

I couldn't see any obvious bulged caps or anything.

Thanks!!!

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

first of all....take the screen in part and turn on with out screen you can see if there any fault at led.... if there no fault then back here.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

I don't think it is LED's because they all light up fine for 5-10 seconds and sometimes more if the TV has been unplugged and sitting for a while. It has worked for more than an hour when I first plugged it in after having it unplugged for a long time. I also just tried to check what I assume are the standby voltages, which I think are supposed to be 3.5V and I'm reading 7.3V....

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

Well, at least you need to find out if your meter and the battery fir the meter is any good or not.
What happen if your turn down the Backlights level (not brightness) down to 50%?
It looks like some of the LEDs are not on after heating up.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Meter is fine, measures correct voltage in from wall and has fresh battery. I've turned the backlight down all the way to zero and nothing changes. I've had it at 34% for now. It seems to me that there has to be something wrong with the power board because of that 7.3V reading when it is supposed to be 3.5V.

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

Can we see where exactly you measure this 7.3VDC and get the reading of 3.5VDC?
Something would have been badly damaged if it is really that high.
Same for this on post 1" The 24v pwr on is reading 7 volts."
"Meter is fine, measures correct voltage in from wall" But that is AC reading, how about DC reading on for I.E. BATTERIES?
Has to be error in measurement.

[Andrew F. Ali]

Re: LG 55LS4500 Dim Bars Across Screen

Weak LEDs....Backlight not fully on.....Suspect vdc reading not taken correctly as the LOW voltage for the 24Vdc and HIGH voltage for the 3.5Vdc will shutdown the SMPS. For those dc measurements use the chassis-GND as -ve for your meter.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Well guys, thanks for catching my rookie mistake. I hadn't switched to DC volts. Here are the detailed readouts:

24V PWRon : 3.41
24V : 25.1
3.5V : 3.58 (stby) 3.53 (on)
3.5V : 3.58 (stby) 3.53 (on)
12V : 12.25
12V : 12.25
12V : 12.25
Pdimm1_error : .11

LED's:

VC1 : 25
VC2 : 16.8
VC3 : 18.4
VC4 : 18.2
VC5 : 17.8
VC6 : 18
VC7 : 18.1
VC8 : 18
VC9 : 18
VC10: 18.4
VC11: 17.9
VC12: 24.9

LED+: 76.6

So the thing in question I guess is the 24V PWRon? I tried to take a reading as I turned on the tv and still had 3.4V.. don't know if that is out of wack but kind of seems like it is. Also the voltages on VC1 and VC12 seem to be a little high? And VC2 is a little low? Not sure..

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Also not sure about the Pdimm1_error.

Interesting thing of note I thought - I checked the voltages for VC1 and VC12 on tv startup when all the LED's light up fine. Those both measure around 18.6V until the bars decide to appear and then the voltage goes up to 25V...

[ReeceyBurger123]

Re: LG 55LS4500 Dim Bars Across Screen

Shorted Leds in the backlight, might be best to take the panel apart as Diah says so to test them as shown in my videos.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Okay, I have started to think more about Leds. I probably am going to take the panel apart soon, but would you still think it's shorted Leds even if the screen worked for a while when I hadn't had it on for a time? And it's not always full bars that show up on the screen, sometimes it's just like half of a bar.. Is the 3.4V on the 24V PWRon okay? Would there maybe be something wrong on the PS/Led driver board?

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

"24V PWRon : 3.41" 24V PWRON is the command signal from the Main board to turn on the 24V power supply, <1VDC = OFF, >2V or higher = ON.
I would say VC1, VC12 are bad.
How about adjust the Backlights level down to 50% (NOT BRIGHTNESS) to see what will happen?

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Hey budm, thanks for the insight. I currently have the backlights (not brightness) down to 25%. The same thing still happens.

You think it's the LEDs themselves and not something on the PS board? When I turn the TV on just now, only the top right corner LED has dimmed. Then after a couple minutes, the top left corner dimmed which produced the dim bar effect, and also a part on the left side dimmed. I think this is an edge-lit TV, could it be that the top right edge LED or LEDs are shorting and not allowing the correct current to flow through to the other ones if they are in series. But why would it only affect the top half of the screen?

Attached another picture of semi-dimmed.

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

Hey budm, thanks for the insight. I currently have the backlights (not brightness) down to 25%. The same thing still happens.

You think it's the LEDs themselves and not something on the PS board? When I turn the TV on just now, only the top right corner LED has dimmed. Then after a couple minutes, the top left corner dimmed which produced the dim bar effect, and also a part on the left side dimmed. I think this is an edge-lit TV, could it be that the top right edge LED or LEDs are shorting and not allowing the correct current to flow through to the other ones if they are in series. But why would it only affect the top half of the screen?

Attached another picture of semi-dimmed.

why don't post photos on of the power supply and how many cable groups going to main boards... if they are 2 sockets then you have other issue with local dimming.

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

https://www.badcaps.net/forum/attach...4&d=1480374011
It looks to me that the LEDs on the right are all on at lower level backlights setting because if you look your pictures above form post 1, you have dark shades on left and right side of the screen. You will need to replace the LEDs.
Now you only have on the left side.
https://www.badcaps.net/forum/attach...2&d=1480535200

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

switch it to service menu ( EZ_adjust ) and turn OFF local dimming.. then check ----- if you don't like to take screen in part or upload photos as requested.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Okay, if I let the TV sit it eventually goes to the top two bars and lower left corner that dim like in the first picture I uploaded. Here are pictures of the PS board and the main board as requested.

Diah I'm not sure how to get into the EZ-Adjust menu, I can get to the installation menu.

I checked the LED voltages again with those parts dimmed.

VC 1, 3, 7, 10, and 12 all have around 25V going to them. Those seem to be the ones where the bars are. See my third picture for that assumption.

So are we set on LED's then? Could it not be something wacky with the LED driver on the PS board (because the PS board has that LD701 light flashing)? I unhooked the LED cables and started up the TV, and it still gives the flashing light (which makes me think LEDs are okay, problem with PS/LED driver board).

I then plugged in the LED cables to the PS board and checked voltages, which all read around 20v consistently (which makes me think no shorts in LEDs otherwise wouldn't see constant voltage?) The LEDs did not light up the backlight after plugging in their cables with the TV on but the screen was still on as I could do the flashlight test and see it. Don't know if this info helps. Thanks for the help so far all!

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

forget my point to EZ_Adjust and local dimming , your set don't have. so 100% LED fault. take screen in part.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Alright, got busy through the holidays but now I have some time to try and make this tv good. I have it taken apart and I can see the side strips of leds.. where do I go from here? Should I start testing each led individually?

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

turn on your TV with out the screen.. and you will find which LED dimming or going off after awhile.. give time to them till the fault appear