LG 55LS4500 Dim Bars Across Screen

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Here are some pictures for reference of the LED strip. Thanks.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Hey Diah, how do I turn the tv on without the t-con board plugged in?

[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

put them back and turn on your tv with out screen connected. to check with your eyes which LED will go off or dim or blinking etc. at this stage you cant use measurement as it may LED read correct but after while go fault. so visual check most important now at first stage.

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

T-CON keep it install and plunged to main board.. only the LCD keep it out

[maveriik]

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?

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

yes. and use sun glasses to take look deep if there one between other dim or off

[maveriik]

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.

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

now . need to turn off the TV and make each led as diode check it.
also need to messure the led long and wide. i think they are 7030 . mean 7 mm x 3 mm . 6.3 volts forward . check after you are knowing those. write here to drive you where to buy 100 pieces for less than 7 USD

[maveriik]

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?

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

Or that must just be because I'm powering those LEDs with the 9V from the multimeter...

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

Or that must just be because I'm powering those LEDs with the 9V from the multimeter...

wrong. LEd should be tested one by one as Diode. not as group. because if one LED of this group cut off then all the rst will be off. either if one get shorted the complete group will be go to Zero V. and the tv register error.
so if one or more you have fault.. the time now to replace LEDs how much you can you are good to have new backlight.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

wrong. LEd should be tested one by one as Diode. not as group. because if one LED of this group cut off then all the rst will be off. either if one get shorted the complete group will be go to Zero V. and the tv register error.
so if one or more you have fault.. the time now to replace LEDs how much you can you are good to have new backlight.

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..?

[Diah]

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..?

no need to take any out for test... write down the average value you measure of them with yours DMM one by one as Diode test

[maveriik]

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
.671

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

Those readings are the Vf of the protection diode, you need to reverse your meter probes and test them again.

[maveriik]

Re: LG 55LS4500 Dim Bars Across Screen

When I flip the probes around I don't get anything on any of the LEDs...

[budm]

Re: LG 55LS4500 Dim Bars Across Screen

They are dual-LED (6V, LEDs connected in series) then your meter may not be able to test them.

[Diah]

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
.671

this reading to me this groups LED are correct.
we have now issue that the Vf currents cut down after while, since you don't have LED Tester, you can use this method to narrow the fault.

follow the line - of this LED groups to the MB sockets, you need to replace the - line with other groups of the same strips. to see if the fault of this first groups remain or the fault will appear to the group you replaced the - line with.
if the fault show that the other groups turn off after while we have here issue with MB. if the first group keep turn off then need to replace all the 11 LED.

tips to do this test you can do it on the cable which go from MB socket to the strips, at the middle of the way separated the line then cut the one belong to this fault first group with other group line. after repair and test you can easily bring them back as they are.

[Diah]

Re: LG 55LS4500 Dim Bars Across Screen

correct Typo (( MB )) mean PWB