Backlight issue LG 50ln5600

[7thkey]

I have an issue with 3 backlight strings not lighting. I turn TV on top 2 strings light, bottom string lights. Middle 3 do not. Then all backlights turn off due to protect . I tried switching out different working stings to result in always the same result. This model has the led drivers built into power supply. I replaced power supply also same result. I do have picture and sound via flashlight test.

From top to bottom led+ 108 to 78, led- 40, led+ 170 then slowly drops,led- 61.

I have not replaced or tried a bypass jump of main board. I have not replaced the led strip connector board (66371-0021A) it shows no sign of distress or problems.

I've seen similar models have bad LEDs and diodes have been used in place. My problem is not open LEDs as mine all work and check out.

Any help would be appreciated thank you.

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

Leds don't fail open they fail like incandescent light bulbs and just plain don't light due to the whisker inside of them snapping. The leds strips will be wired in series so if one diode fails the rest of the strip wont light. Can you take photos of the inside of the screen and of the strips please.

[tom66]

Re: Backlight issue LG 50ln5600

Leds don't fail open they fail like incandescent light bulbs and just plain don't light due to the whisker inside of them snapping. The leds strips will be wired in series so if one diode fails the rest of the strip wont light. Can you take photos of the inside of the screen and of the strips please.

If they failed open, you would expect the rest of the strip to fail.
If they failed SHORT, then the strip would work but that LED would be out.

[7thkey]

Re: Backlight issue LG 50ln5600

I'll get a picture up tomorrow. Each led strip is made up of 2 strips. They are in 6 rows top to bottom. No matter what set of LEDs I swap in. Only the same 3 rows light up then shut off. If I swap the lighting 3 with the non lighting 3 the same three rows continue to light . At first I believed 3 rows of LEDs were bad and needed replaced. I swapped those rows with the working LEDs and they would not light. The LEDs open or shorted does not seem to be the issue. The issue is what would make 3 entire middle rows not light up if the LEDs on those rows are all in working order?

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

Ahh right ok and how are they connected, as in what type of connectors go to the leds ?

[7thkey]

Re: Backlight issue LG 50ln5600

Ahh right ok and how are they connected, as in what type of connectors go to the leds ?

They have a plastic plug in type connector.

This is the direct replacement parts for it.. Each LED string is 2 pieces that attach to one another forming 6 long strings that connect to that board by the same plug in.

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

Hmm ok, in the past I have had issues with them plastic plugs corroding and not making a proper connection to the strips. Do you have a multimeter so you can see if there is continuity between the connections to see if the connection is being made and working ?

[7thkey]

Re: Backlight issue LG 50ln5600

Hmm ok, in the past I have had issues with them plastic plugs corroding and not making a proper connection to the strips. Do you have a multimeter so you can see if there is continuity between the connections to see if the connection is being made and working ?

The LED strips do have a + - test points. I believe I can test them in diode mode. I'll try that tomorrow and get some readings. I really don't think its a contact though as I can switch out different strips and they light up in the working rows.

[7thkey]

Re: Backlight issue LG 50ln5600

Pictures of LED setup.
Second picture shows one set lit 3 sets light up and then go out fast . I have swapped out all LED strips and no LEDs are out.
In the last picture I labeled them 1-6 to show voltage (red x indicates does not light up on start up) the red x LED strips do work though if I swap them.
1) 63v
2) 170-78v
3) 146-55v
4) 50-0v
5) 110v-78v
6) 86v-55v

The first voltage is power on voltage.
The second voltage is the constant it ticks down to and stops at.

Well it won't let me upload the photos. I'll try later I guess

[7thkey]

Re: Backlight issue LG 50ln5600







3rd pic upside down not sure why sorry.

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

Wait so when you swap the strips into the others position they light ?

[7thkey]

Re: Backlight issue LG 50ln5600

Wait so when you swap the strips into the others position they light ?

Ya if I put the non lighting LED strings in the 3 spots that light they light up. Clearly position 4 is where the voltage stops. I have tested that strip and nothing it lights up fine in the top spot. So what would cause one string to get no voltage on power up? The green connection board is 6637L-0021A. The power supply EAX64905501 v2.2 was swapped out for another same version I was told was tested and working properly. I guess it is possible I got a bad board but to both have the same LED string out is unlikely. Is it possible the motherboard could be not sending the signal to the LED drivers on the power supply? Is there a way to run the power supply not connected to the motherboard (jumper maybe)?

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

Right I know you may have done this already but, carefully check all the strips and use a pen or something to mark off the strips so that you know they are definalty good. I dont think that the mobo is at fault possibly the boost converter but sounds like a tricky one.

[7thkey]

Re: Backlight issue LG 50ln5600

Right I know you may have done this already but, carefully check all the strips and use a pen or something to mark off the strips so that you know they are definalty good. I dont think that the mobo is at fault possibly the boost converter but sounds like a tricky one.

All strips are good. I have done the diode to ground test and each one separate . Every led lights then fades properly as the remaining voltage is drained. So boost converter? On what board is that as I already replaced the power supply/LED driver board?

[Agent24]

Re: Backlight issue LG 50ln5600

Ya if I put the non lighting LED strings in the 3 spots that light they light up. Clearly position 4 is where the voltage stops. I have tested that strip and nothing it lights up fine in the top spot. So what would cause one string to get no voltage on power up? The green connection board is 6637L-0021A. The power supply EAX64905501 v2.2 was swapped out for another same version I was told was tested and working properly. I guess it is possible I got a bad board but to both have the same LED string out is unlikely. Is it possible the motherboard could be not sending the signal to the LED drivers on the power supply? Is there a way to run the power supply not connected to the motherboard (jumper maybe)?

It sounds to me like that Green board on the end that all the LED strips connect to is bad at some places. Maybe some of the connectors are bad or there are broken traces or cracked solder joints. That would fit with the strips lighting or not lighting depending on which position you plug them into.

Have you checked for continuity between the plug from the PSU and the outputs to each of the LED strings?

[7thkey]

Re: Backlight issue LG 50ln5600

I did in the start of the post . I measured the 2 led+ and 2 led-. I have not replaced the thin green board yet. That's my next step unless someone chimes in on what would cause one string to get no voltage. I've tried 2 different power supply's.

[7thkey]

Re: Backlight issue LG 50ln5600

So today I measured the voltage on the 4 points on the plug that connects to the thin green led board. Before they enter board they are 78,0,78,0 that seems up to spec. I'm thinking at this point replace all LED strips and that green board. The LED strips may light up fine but if one is triggering the protection shut off.

[Hamie]

Re: Backlight issue LG 50ln5600

Maybe it's just not making a connection, what about dabbing a bit of solder on the Led strings so it fits tighter into the harness.

[ReeceyBurger123]

Re: Backlight issue LG 50ln5600

I agree with Hamie add some fresh solder to the points. If that fails pull off the plastic connector thats at the end of each strip and bridge the gap with solder and some wire.

[Hamie]

Re: Backlight issue LG 50ln5600

You may not actually need to desolder the connector, most led strips have a + and - points, you could simply connect those points with a bit of wire to the board.