Repair led board of imac lcd

[mike01]

Hello,

i am trying to repair my led board from imac 27 lcd mid 2011. There are plenty of white smd leds on this board. Three of them where broken and so they emit blue light which should be white. I have searched via internet a lot of sites and the manyfacturer of this kind of smd leds (young lightning) but i could not find the same. Does anybody knows where i can get them or which alternative smd leds i could buy? Maybe someone knows where i can find the whole led board.

Thx

[Alex Eisenhut]

Check eBay but seems many LEDs may be of low quality.

If you can take close clear pictures of the LEDs and measure the voltage drop across a good one, that can narrow it down.

[wraper]

If you have some dead laptop, smartphone or desktop monitor screen with led backlight, then you could find there something similar. In my experience all LEDs were of the same form factor. If you can make a picture and write dimensions, I could check if I have something similar. I also can send a complete flex cable with such LEDs salvaged from laptop/smartphone or tablet LCD at the expense of shipping.
Actually I have backlight salvaged from sony tablet with flex marked with YOUNGLighting. Doesn't mean that leds are of the exactly same light output though.

[poot36]

The LEDs still work but I think that the phosphor that takes in the blue light and converts it to white light has come off.  I know that you can get plastic that is coated with this stuff (it is in the Philips tri shaped bulb) so maybe you could get it in a paint and just dab it on the broken LEDs.  It would be a lot safer then trying to remove smd parts off a flexible pcb.

[mike01]

Thank you all for your quick reply.The lcd is at one of my friends pc shop cause there was enough space to strip all the lcd.
I will check all that solutions you' ve written and will reply with photos 

[mike01]

Hello again i have uploaded the photos you asked me to show you of the leds.
Maybe you can help.

broken led on the board

good leds on the board

leds on the board without cap

pcb of the led

led of the board and no cap

Sorry but i don't have any other specs for the leds.

[wraper]

I don't have such. Do this display have wide color gamut? I would say that those seem to be GB-LEDs as it seems to be 2 dies in one package. One die is green, second is blue with red phosphor on top. If green led is dead it should emit purple color I guess. I also see that one one photo phosphor is transparent on one side, thats weird.

[wraper]

Googled a bit, 2011 imac don't seem to be wide color gamut, so they mighht be just weird regular LEDs

[wraper]

Anyway, you might get a hard time to get those. As it likely have the same LG  LCD panel as used in most 27"LED monitors, it might be worth to get some broken 27"screen with sRGB color gamut for parts. For example from dell U2713HM (not U2713H which is wide color gamut). As the panel itself should be the same, you could replace all backlight unit without worries that leds will have uneven brightness.

[mike01]

Do this display have wide color gamut?]

If you mean the backlight gamut than i believe it has only few ones.

On the last photo when you zoom in you can see that there is an 4 x 4 matrix
maybe there are these leds you say. Where can i found such GB-LEDs?

[wraper]

no, color gamut is about how many colors monitor can show. Anyway your display seem to be using regular panel.

[wraper]

I don't think you can get them otherwise than salvaging from broken lcd panel.

[mike01]

thx for the additional information

maybe it is better to buy a new display or purchase one from ebay

[mike01]

Hello again my friend has mentioned that the leds are 2,5V if this gives more light to the problem.

[blob810]

Hello Mike,

i have the same problem here on my iMac 27 Late 2009.
Did you already solve the problem and give me a tip where i can buy those led´s.

Thank you

[wraper]

As you are two already, you could make a group buy of dead lcd panel to salvage the leds