LG 55LM4600 faulty LED Driver or Backlights?

[tvfixer007]

Any idea what the cause of this could be? I have a dark spot on the right side of the screen. When I go to the menu and turn screen off, and then press a button on the remote to turn screen back on the dark spot is gone for 5 seconds. Every time I do that the dark spot goes away for 5 seconds and comes back.

I originally presumed it was a bad LED.... but it doesn't make sense to me that it would work for 5 seconds then stop!?

https://www.youtube.com/watch?v=dUi1...ature=youtu.be

[JeffJ]

Re: LG 55LM4600 faulty LED Driver or Backlights?

This is an edge lit tv and its clearly one of the banks of edge lighting failing. The fact it works for a few seconds is weird.

If i had to guess that bank on the right side has a dead shorted led and the PSU is shutting down that PWM bank when it detects abnormal draw.

[budm]

Re: LG 55LM4600 faulty LED Driver or Backlights?

It does look like some LEDs in that section shorted out so the circuit goes into over current shutdown.

[tvfixer007]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Was hoping it wasn't bad LEDs. Kind of figured it was but I thought if LEDs are shorted they don't work at all.

I'm going to take the panel apart when I wake up in the morning and test all the LEDs.

[budm]

Re: LG 55LM4600 faulty LED Driver or Backlights?

LEDs are connected in series to form LED strings, there may be 4 strings of LEDs used in that panel, so if some are shorted out the rest if the LEDs in that string will still light up, like Christmas lights..

[CapLeaker]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Looks like an LED failure to me too...

[tvfixer007]

Re: LG 55LM4600 faulty LED Driver or Backlights?

I took out the strip and tested the LEDs one by one with a battery. They all lit up and were relatively close in brightness. Also in the attached image if I touch my meter probe or any metal tip on the PDIM and PDIM2 (J47, J44) jumpers the backlights flicker.

Leaving the TV on for a while the left side LED strip starts acting up in the same manner. Which is really confusing me. Why would the other LED strip start acting up much later?

When that first section of LEDs cut off, they are actually still on with a very faint glow coming from them.

[martino]

Re: LG 55LM4600 faulty LED Driver or Backlights?

I would have plugged the strip back in and let the tv drive them,that way you could see them fail after a few sec. Battery testing them prob didn't trigger the defective one.

[DOPPLERBOB]

Re: LG 55LM4600 faulty LED Driver or Backlights?

It's most likely an LED failure at full operating current. The battery test is good to weed out open or shorted LED's, but it really doesn't test the LED's under normal operating current and after they heat up. I had the same problem. I operated the LED's normally with it taken apart so I could watch. I sped up the process by using a hair dryer on the suspected defective area. One LED would open up and the whole strip of 6 goes out (in series). Turned out to be a bad solder connection to the LED.

[CapLeaker]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Plug the LED's back in, put your DMM to DC V and probe each LED string while turning the TV on. That will give you a clue on which string the problem is. LED's can fail like that. They may work for 5 seconds or even 5 or 20 minutes then go out. You can try to turn the back light down to next to nothing and probably the LED will stay on longer.

[tvfixer007]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Plug the LED's back in, put your DMM to DC V and probe each LED string while turning the TV on. That will give you a clue on which string the problem is. LED's can fail like that. They may work for 5 seconds or even 5 or 20 minutes then go out. You can try to turn the back light down to next to nothing and probably the LED will stay on longer.

I realize now how stupid I am! I found the bad LEDs but these things are way too hard to remove! So I'll be ordering new strips instead, and I'll post my final result when I get the TV back together.

[CapLeaker]

Re: LG 55LM4600 faulty LED Driver or Backlights?

I realize now how stupid I am! I found the bad LEDs but these things are way too hard to remove! So I'll be ordering new strips instead, and I'll post my final result when I get the TV back together.

Sounds like a plan...

[tvfixer007]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Hello,
we're sorry to inform you that one of the LED strips you purchased has been damaged during shipment. We shipped the items out yesterday and USPS brought the package back this morning only for us to see that the strips had been damaged beyond repair. At the moment we only have one strip left to be able to replace and that is the Led Backligth Strip LG 55LM6200 6922L-0003A 6920L-0001C 6916L0782A (strip and holder) #L0003A. We can refund you the complete cost of the other LED since we cannot replace that one at this time, but we can still ship out the 6922L-0003A. If you would like us to ship that part out, please let us know and we'll refund you the cost and ship it out again today! We apologize for any inconvenience this causes you and we hope you understand.
Thank you

--
Michael Barriel
MBS Electronic Inc. & MyShopTV

So much for fixing this TV. I found 2 strips for $32.99, and they said one got damaged in shipping. The one I really needed. Only had to be shipped from Miami to Tampa. Find that kind of odd really.

[dskall]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Don't think they are that hard to replace with heat gun or iron. You could buy strip and replace bad led's with it.

[CapLeaker]

Re: LG 55LM4600 faulty LED Driver or Backlights?

Maybe use Reeceyburger's stacking method. There is a video from him on youtube about that.

[tvfixer007]

Re: LG 55LM4600 faulty LED Driver or Backlights?

These edge lit bars are hard to repair. I messed up the tracing somehow. Just decided to replace both of them with good LEDs. TV is now working great, thanks everyone!