Author Topic: Why do backlight LEDs burn out and go blue?  (Read 19951 times)

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Offline etiTopic starter

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Why do backlight LEDs burn out and go blue?
« on: November 05, 2021, 09:44:34 pm »
Why do backlight LEDs burn out and go blue?

12-11-21: (update) - attached, images of the faulty LEDs being tested. They have around 2.5v drop across them.

I've been given an LG 4K TV, and the backlight LEDs have been left on full whack, and have gone blue... but why does this happen - phosphor diminishing?

(14-11-21) Jump to this post to see macros of the bare LED die and lens type assy: https://www.eevblog.com/forum/chat/why-do-backlight-leds-burn-out-and-go-blue/msg3812753/#msg3812753

Edit (added info): just found this article >> https://jestineyong.com/quick-understanding-of-led-bulb-turning-blue/

https://www.circuitsonline.net/forum/view/148440

For anyone doubting that this is the case, see below:


« Last Edit: November 14, 2021, 09:05:48 pm by eti »
 
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Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #1 on: November 05, 2021, 10:16:58 pm »
They don't.  Your TV is in blue mode.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #2 on: November 05, 2021, 10:31:14 pm »
They don't.  Your TV is in blue mode.

 :-DD
 

Offline amyk

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Re: Why do backlight LEDs burn out and go blue?
« Reply #3 on: November 06, 2021, 12:28:34 am »
That doesn't look like the backlight, but rather (two!) missing channels of video data.
 

Offline IanB

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Re: Why do backlight LEDs burn out and go blue?
« Reply #4 on: November 06, 2021, 12:30:56 am »
Why do backlight LEDs burn out and go blue?

They don't. You have a TV with an undiagnosed fault where the symptom is a blue screen.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #5 on: November 06, 2021, 12:40:45 am »
Why do backlight LEDs burn out and go blue?

They don't. You have a TV with an undiagnosed fault where the symptom is a blue screen.

I beg to differ. Google "LG TV blue picture fault" and count the endless results that show engineers replacing the backlight strips that have gone blue.

I have another spare TV with led backlight (JVC) - would the LEDs be the same if I desoldered the working JVC ones and transplanted them onto the backlight strips of the LG?

Thanks.
« Last Edit: November 06, 2021, 12:42:17 am by eti »
 

Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #6 on: November 06, 2021, 12:44:15 am »
There actually is a blue mode in the service menu of most TVs, but looking more closely at your picture, that might not be it.  Is the white spot in the upper left a reflection or is that the sun appearing in the actual TV picture?

LG has an issue with LED backlights bluing with age, but I've never seen one that bad!  Unless the TV was simply left on in some function where nobody cared what it looked like, I can't imagine watching it long enough for it to get that bad--it takes years and years.  Why they do it I don't know, but it is a defective part.  A few minutes of disassembly will suffice to determine if this is the case.
« Last Edit: November 06, 2021, 12:46:23 am by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline IanB

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Re: Why do backlight LEDs burn out and go blue?
« Reply #7 on: November 06, 2021, 12:45:48 am »
I have another spare TV with led backlight (JVC) - would the LEDs be the same if I desoldered the working JVC ones and transplanted them onto the backlight strips of the LG?

It's impossible to say, since you have an undiagnosed fault with the current TV.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #8 on: November 06, 2021, 12:46:55 am »
I have another spare TV with led backlight (JVC) - would the LEDs be the same if I desoldered the working JVC ones and transplanted them onto the backlight strips of the LG?

It's impossible to say, since you have an undiagnosed fault with the current TV.

Diagnosis: LEDs have turned blue and need replacing. Did you even Google it?

https://jestineyong.com/quick-understanding-of-led-bulb-turning-blue/
« Last Edit: November 06, 2021, 12:50:47 am by eti »
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #9 on: November 06, 2021, 12:49:59 am »
There actually is a blue mode in the service menu of most TVs, but looking more closely at your picture, that might not be it.  Is the white spot in the upper left a reflection or is that the sun appearing in the actual TV picture?

LG has an issue with LED backlights bluing with age, but I've never seen one that bad!  Unless the TV was simply left on in some function where nobody cared what it looked like, I can't imagine watching it long enough for it to get that bad--it takes years and years.  Why they do it I don't know, but it is a defective part.  A few minutes of disassembly will suffice to determine if this is the case.

Yes, the bright spot upper left is a reflection. There seems to be a lack of understanding with others in this thread about exactly how white LEDs manage to emit white light - it's UV light which strikes a phosphor and that causes the phosphor to emit white light (I forget the physics term).

Yep LG definitely have an issue, and they also had HUGE numbers of issues with their smartphones a few years ago (different faults). A brand to avoid.
 

Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #10 on: November 06, 2021, 12:50:22 am »
I have another spare TV with led backlight (JVC) - would the LEDs be the same if I desoldered the working JVC ones and transplanted them onto the backlight strips of the LG?

Unless they are the same size and voltage--the LEDs are in series--no.  If you really do have the worst case of blue tint imaginable, then there are places that sell replacements.  What model is the TV.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #11 on: November 06, 2021, 12:53:07 am »
I have another spare TV with led backlight (JVC) - would the LEDs be the same if I desoldered the working JVC ones and transplanted them onto the backlight strips of the LG?

Unless they are the same size and voltage--the LEDs are in series--no.  If you really do have the worst case of blue tint imaginable, then there are places that sell replacements.  What model is the TV.

Actually it's nowhere near that blue in reality - more like a mid purple haze (makes sense as it's UV).

The TV is an LG 43uj630, and I've found the strips but would like to try the free repair first 😁

Thanks mate.
 

Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #12 on: November 06, 2021, 12:58:30 am »
Yes, the bright spot upper left is a reflection. There seems to be a lack of understanding with others in this thread about exactly how white LEDs manage to emit white light - it's UV light which strikes a phosphor and that causes the phosphor to emit white light (I forget the physics term).

Luminescence.  And it's widely known.  It's just a bit unusual to see white LEDs go that bad and still all work.  Perhaps they run too hot?  Was this used as some sort of static display or just someone's television?
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline IanB

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Re: Why do backlight LEDs burn out and go blue?
« Reply #13 on: November 06, 2021, 01:00:22 am »
There seems to be a lack of understanding with others in this thread about exactly how white LEDs manage to emit white light

No, there is a lack of understanding by certain people in this thread about how to diagnose faults. You have a probable cause, even a very likely cause, but you have not proven it to be the case. Especially since you posted a picture of a blue screen, but now you tell us it is not actually blue, but a kind of purple-hazy.

I'm seeing a pattern of you creating antagonizing threads, which means you are going into my ignore list. Goodbye.
 
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Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #14 on: November 06, 2021, 01:02:39 am »
Yes, the bright spot upper left is a reflection. There seems to be a lack of understanding with others in this thread about exactly how white LEDs manage to emit white light - it's UV light which strikes a phosphor and that causes the phosphor to emit white light (I forget the physics term).

Luminescence.  And it's widely known.  It's just a bit unusual to see white LEDs go that bad and still all work.  Perhaps they run too hot?  Was this used as some sort of static display or just someone's television?

It was in an old folks home. These questions have no answers I can give. Yes it’s widely known - you and I know that. IanB seems to think it’s “undiagnosed” when I can see the leds through the grilles in the rear of the set, glowing this purplish blue…

I’m not wanting to be awkward or rude, IanB, but it’s very much diagnosed. I’m moving on from that point, not backwards to an imagined other misdiagnosis.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #15 on: November 06, 2021, 01:03:32 am »
There seems to be a lack of understanding with others in this thread about exactly how white LEDs manage to emit white light

No, there is a lack of understanding by certain people in this thread about how to diagnose faults. You have a probable cause, even a very likely cause, but you have not proven it to be the case. Especially since you posted a picture of a blue screen, but now you tell us it is not actually blue, but a kind of purple-hazy.

I'm seeing a pattern of you creating antagonizing threads, which means you are going into my ignore list. Goodbye.

Wow. Okkkkk then. 

Blue, purplish blue, purple, whatever - what’s the difference? When a WHITE LED is meant to be white, splitting hairs over the shade of purple or blue that it’s clearly not meant to exhibit, might actually show that the antagonist is someone else. Ignore me if you wish, you’ve not helped the thread and clearly just want to storm out in a temper and make a flourish. Great.

I wasn’t asking IF the LEDs are the wrong colour, I asked why they go that way.

🤦‍♂️🤯
« Last Edit: November 06, 2021, 01:07:32 am by eti »
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #16 on: November 06, 2021, 01:18:53 am »
That doesn't look like the backlight, but rather (two!) missing channels of video data.

Thanks for the reply. Actually one can see the LEDs glowing this bluish purple through the grilles in the back of the set. Also the camera puts a very blue cast on what is, in actuality, a more purple hazy screen.

Looking past the "purple haze" one can see all the RGB data is present, as it's colour with a purple overly - it's nowhere as exaggerated as in the photo.
« Last Edit: November 06, 2021, 01:20:43 am by eti »
 

Offline amyk

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Re: Why do backlight LEDs burn out and go blue?
« Reply #17 on: November 06, 2021, 03:03:28 am »
I think you're being met with incredulity because that is an insanely blue photo you've taken, and while a few bluish patches would be clearly phosphor degradation, they must've really messed up a whole batch of LEDs for them to all go bad like that.

If you open it up and show the backlights themselves, that would clear up a lot of the disbelief.

"Roses are red,
violets are blue
so are these LEDs
but they can't believe it's true."
« Last Edit: November 06, 2021, 03:06:29 am by amyk »
 

Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #18 on: November 06, 2021, 03:16:03 am »
Here's my TV in blue mode.  It has no LEDs.  The picture is pretty close to the way I saw it and I've never seen an LED-backlit TV look anything remotely similar.  Like the OP, the only visible light that isn't blue is a reflection.

« Last Edit: November 06, 2021, 03:17:34 am by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline etiTopic starter

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Re: Why do backlight LEDs burn out and go blue?
« Reply #19 on: November 06, 2021, 03:32:40 am »
I think you're being met with incredulity because that is an insanely blue photo you've taken, and while a few bluish patches would be clearly phosphor degradation, they must've really messed up a whole batch of LEDs for them to all go bad like that.

If you open it up and show the backlights themselves, that would clear up a lot of the disbelief.

"Roses are red,
violets are blue
so are these LEDs
but they can't believe it's true."

I've no desire to "prove" it to one bloke who's gone off in a tantrum and blocked me. Meh.

If you Google the symptoms it's EVERYWHERE and extremely widely known re LG LED backlit TVs.

If that bloke  can be bothered to form a pedantic reply on a forum, he can at least use those typing fingers to do a TRIVIAL bit of research for about 5 mins.
« Last Edit: November 06, 2021, 03:36:59 am by eti »
 

Online Siwastaja

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Re: Why do backlight LEDs burn out and go blue?
« Reply #20 on: November 06, 2021, 08:13:26 am »
More likely the backlight consists of RGB LEDs and R, G have failed for a reason or another. Or, the signal chain has failed regarding R and G.

Very unlikely this is due to using white LEDs with slowly failed phosphors to the point image is completely blue. But of course, that's possible, too.

The fact that others have seen the same failure to the point it's a very common issue is interesting, because it should indicate someone knows the likely cause. This should make your life easier; Google further until you find an explanation from someone who actually investigated what's wrong. But obviously if you refuse to investigate and fixate into the initial idea of white LED phosphors failing like in one documented case in an LED lightbulb with external phosphors, then there is nothing we can do.

Fixation is a bitch. Airplanes have crashed thanks to fixation. I feel sorry for you, but good luck.
 

Offline Twoflower

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Re: Why do backlight LEDs burn out and go blue?
« Reply #21 on: November 06, 2021, 10:14:55 am »
Could that be that the TV uses kind of 'remote phosphor'? Some TV-Sets use blue LEDs with a bar contain the phosphor or nano-crystals (most of them contain cadmium!) to transform the blue light to the specific spectra required. If that piece fell off/moved that only the light from the LEDs enters the diffusor of the LCD?

But often there are LEDs on two edges (if not spread over the background). That would rule out the idea the the remote phosphor bar is the culprit unless both fell of the same way. Unless the TV experienced any kind of stress (quick change or high temperature, vibartion...) that made fell off the phosphor?

EDIT: I missed the point that you actually mentioned that it was on at full whack. So the LEDs ran hot and the phosphor might have been damaged/detached from the LEDs.

I think RGB LEDs for background illumination is not commonly used anymore. From what I've heard too many problems with the uniformity of the used LEDs (brightness, aging, color...) and too expensive.
« Last Edit: November 06, 2021, 10:29:22 am by Twoflower »
 

Offline bdunham7

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Re: Why do backlight LEDs burn out and go blue?
« Reply #22 on: November 06, 2021, 02:26:39 pm »
Here's a photo of failed LED strip from such a TV.


A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Online themadhippy

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Re: Why do backlight LEDs burn out and go blue?
« Reply #23 on: November 06, 2021, 02:50:10 pm »
Quote
They don't.  Your TV is in blue mode
is that for viewing adult movies?
 

Offline ealex

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Re: Why do backlight LEDs burn out and go blue?
« Reply #24 on: November 06, 2021, 05:58:53 pm »
@bdunham7: that's exactly how the leds looked like in the LG i've recently repaired.

the phosphorus layer was flaking off, and most of the leds where pure blue.
there where no signs of overheating.

the fix was easy, but handling the huge glass pane is scary

@eti - i don't think you can desolder those, they are bare dies on the pcb, with a lens glued above.
the replacement led strips are cheap, just take care to get the proper ones, and maybe some good / thin double sided tape
 
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