55la6205 backlight issues

[speedymmx]

Re: 55la6205 backlight issues

OK so I took the TV apart and i'm down to the LED stripes panel, how can I test or find out which ones are bad?



Thanks

[ReeceyBurger123]

Re: 55la6205 backlight issues

You have a Dmm ?

[ReeceyBurger123]

Re: 55la6205 backlight issues

Its not going to be easy I tell you !

[speedymmx]

Re: 55la6205 backlight issues

You have a Dmm ?

Yes I have one, I haven't turn the TV on or done anything yet..

[speedymmx]

Re: 55la6205 backlight issues

Ok so I decided to turn on the TV and all the LEDs light up fine? but still shuts down after a bit, how do I find out if there is an open circuit on which LED strip ??

I thought if there was a bad led it will simply just not light up???

Thanks

[ReeceyBurger123]

Re: 55la6205 backlight issues

Ok, right you see the little connectors between the Led strips seen them become flacky and corroded after time and they fail to make contact tripping the whole BL possibly worth removing the strips and adding some fresh solder to them.

[budm]

Re: 55la6205 backlight issues

You do have video source connected to the TV so it will not go into standby, right?
Same Voltage readings as in post #5?
This is what I got:

When the backlight is on and working, showing the LG logo floating across the screen the DCV are as follows from left to right connectors

LED + 133.5
LED - 32.9
LED + 177.5
LED - 43.1

When the backlight randomly turns off the DCV are:

LED + 84.4
LED - 5.36
LED + 84.4
LED - 166.0 this readout goes up and down from 177 down to 166...
Something does not add up with those readings.

[speedymmx]

Re: 55la6205 backlight issues

just took another reading and I see some changes on the -

LED + 133.5
LED - 5V
LED + 177 still higher than the other positive
LED - 5V

when the backlight goes out the second + that is at 177 goes up to 200 now until it slowly goes down to 84V.

anything else I can test????

[budm]

Re: 55la6205 backlight issues

I look look at the LEDs trips in the pictures and I can see Seven strips (12 LEDs per strip), there are two LED driver circuits so one driver must be driving 3 strips (36 LEDs) and another one drives 4 strips (48 LEDs), so that may explain why one has higher Voltage than the other.

'when the backlight goes out the second + that is at 177 goes up to 200 now until it slowly goes down to 84V.' It should not go up unless the load is not connected, you do not see the Voltage rise on the one with 133.5V reading?

[speedymmx]

Re: 55la6205 backlight issues

Just took the reading again the + with 177 is steady at that voltage when the backlight is on, I waited until it shutdown and it went up to 215V and started coming down slowly.

Unplugged waited 2 minutes did the same with the other + 135 steady and when the BL shutsdown there are no power surges or anything just starts to come down to 84V slowly......

[budm]

Re: 55la6205 backlight issues

That means that LED strings connected to that 177V pin has gone open circuit(the Voltage will rise when the load is not present, or the return line that goes to the PWM Power MOSFET has stop conducting. I still think one or more of the LEDs have gone open circuit in the top four LED strips after they warm up.
You have already check and reseat the connectors for those 4 LED strips (the top four).
It looks like you can swap the LED strips to see if the Voltage will rise on the 133V driver.

[ReeceyBurger123]

Re: 55la6205 backlight issues

Thats why I said about the connectors Budm.

[ReeceyBurger123]

Re: 55la6205 backlight issues

Ive seen them break down weirdly, sometimes on start up and sometimes while on/intermittent connector.

[budm]

Re: 55la6205 backlight issues

That is why I asked the OP again since he did not indicate if he did as you have suggested in post 26.

[speedymmx]

Re: 55la6205 backlight issues

That is why I asked the OP again since he did not indicate if he did as you have suggested in post 26.

hi, Guys, no I haven't checked the connectors on the strips, I will do it now and see if it anything changes.

Thanks

[speedymmx]

Re: 55la6205 backlight issues

OK so i reseated the strips and connectors and now the TV wont turn on at all.
All I get is a quick flash of some of the leds and that's it, so something happened when I reseated the connectors and moved the strips???

[budm]

Re: 55la6205 backlight issues

OK so i reseated the strips and connectors and now the TV wont turn on at all.
All I get is a quick flash of some of the leds and that's it, so something happened when I reseated the connectors and moved the strips???

I think you found the cause of the problem, there is/are bad connections/solder joints on the LEDs strips connectors/wire terminals that you will need to locate, clean, and re-solder.

[sdogs]

Re: 55la6205 backlight issues

OK so i reseated the strips and connectors and now the TV wont turn on at all.
All I get is a quick flash of some of the leds and that's it, so something happened when I reseated the connectors and moved the strips???

Hi, :-)
I have the same TV, in the European format has the name 55LA620S, I have a very similar problem to yours, specifically, at times, remains switched on for many hours without any problems, sometimes the backlight turns off after a few moments. In any case the defect is manifested in a completely random way.
I purchased a new psu and are waiting to receive it but, after your post, I think I have some serious doubts about the psu.
You have found the solution to the failure?
best regards
Sdogs

[jdaproduca]

Re: 55la6205 backlight issues

You need to tear the panel open and resolder the connectors that look like the ones in the picture. Over time with the heat the connector develops cracks and oxidizes.

[Kjata]

Re: 55la6205 backlight issues

Hi speedymmx,

I have the same model of tv with the same exact issue, were you able to fix yours?