Re: LG 55LA740V Intermittent backlight band troubleshooting help.
Hi Corky,
I think I looked on ebay or amazona and found the entire metal strip with the led's on it. I ended up buying both the left and right instead of trying to find the exact led's that were bad and replace them. I remember I searched for a while but I found them! Good luck, I know there's got to be a couple out there......
maveriik
Member
Last Activity: 02-12-2018, 09:03 PM
Joined: 11-23-2016
Location: Mesa
-
Re: LG 55LA740V Intermittent backlight band troubleshooting help.
To give closure for my problem (slightly different tv version LG55LS4500), the thing that was causing the bands were the LED strips. I ended up just replacing the LED strips (they were on the sides, causing bands from left to right). If your led strips are on the top and bottom, they might be a likely culprit.Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
When I flip the probes around I don't get anything on any of the LEDs...Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Not sure if I'm doing it right, but here's the measurements I got for the first 11:
.673
.672
.671
.673
.673
.670
.672
.671
.672
.671
.671Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Okay, so are you saying I need to desolder all 11 of the group from the top right that go off and test them then? Because right now I get mostly the same reading on all of them..?...Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Or that must just be because I'm powering those LEDs with the 9V from the multimeter...Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Okay, so I turn off the power and then put my multimeter on diode mode? I checked the first 11 LEDs and they showed around .68 with the leads reversed.
Interestingly enough while I had one end of the multimeter on one of the LEDs that was out, I touched the metal of the tv and the LEDs came back on.. Does this mean that the LEDs are okay, and there is just a ground connection that gets too weak when it gets hot?Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Yeah those are bright. Okay well the first fault just appeared, in the top right corner (I have the picture a few posts back where it shows the dim spots). I checked the voltage to the LEDs when everything was good, and it seemed like the average good voltage was around 17VDC. Now when the top right corner went out (the first 11 LEDs on the top right side) the VC_1 voltage jumps to 24.5 and VC_2 has always looked a little low at 16.5VDC.Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Alright, I have the TV on. All the LED's are currently lit up but now I'll just wait for the problem to show up?Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Hey Diah, how do I turn the tv on without the t-con board plugged in?Leave a comment:
-
Re: LG 55LS4500 Dim Bars Across Screen
Here are some pictures for reference of the LED strip. Thanks....Leave a comment:
-
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?Leave a comment:
-
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.
...Leave a comment:
-
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...Leave a comment:
-
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?Leave a comment:
-
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...Leave a comment:
-
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...Leave a comment:
-
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.Leave a comment:
-
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....Leave a comment:
-
LG 55LS4500 Dim Bars Across Screen
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...
No activity results to display
Leave a comment: