Fixed another iMac with failed LED bar (single LED failed)

[howardc64]

iMac 11,3. This one only had a single LED that failed.

Symptom, can only keep backlight on minimum. Light shuts off instantly if increase brightness. iMac still running. Can see high contrast image (About This Mac popup against black wall paper) with flash light test. Reduce brightness did not recover backlight. Have to reduce backlight level fully with keyboard, sleep (option+command+eject) followed by wake and backlight comes on again at minimum brightness.

Replaced inverter board with a 12,2 board and backlight would stay on at higher brightness (but still had various backlight flickering issues) which revealed a single failed LED (confirmed by LED tester after removal)



Fully disassemble and replace the LED bar fixed this

Apple Thunderbolt Display Black Blanking Out Repair

Thunderbolt Display uses an LG edge LED lit LCD Display (also 09-11 27" iMacs and 27" Cinema Displays). The LEDs are on the bottom edge of the...

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[Nguyen Duc Hieu]

iMac 11,3. This one only had a single LED that failed.

Symptom, can only keep backlight on minimum. Light shuts off instantly if increase brightness. iMac still running. Can see high contrast image (About This Mac popup against black wall paper) with flash light test. Reduce brightness did not recover backlight. Have to reduce backlight level fully with keyboard, sleep (option+command+eject) followed by wake and backlight comes on again at minimum brightness.

Replaced inverter board with a 12,2 board and backlight would stay on at higher brightness (but still had various backlight flickering issues) which revealed a single failed LED (confirmed by LED tester after removal)

View attachment 2461250

Fully disassemble and replace the LED bar fixed this

I assumed you could replace the defected LED cell... Of course, if you have a LED bar in stock, you won't have to go to that extent of repair.

 

[howardc64]

I assumed you could replace the defected LED cell... Of course, if you have a LED bar in stock, you won't have to go to that extent of repair.

Yes. Will try to replace LED cell to see if possible to succeed and report back. LED has a clear dome above with yellow phosphorus coating to convert blue LED to white color. Wonder if that will survive applying heat from under the bar to desolder LED. Discovered this when I accidentally popped off a couple to domes in prior repair efforts.

Also when I reflow the solder joint on each 4 corners of the LED, I notice the LED color temperature changed.

Finally, this iMac appears to be an graphics artists machine with heavy use. Signs are usually failing LED solder connection, LCD has some faded edge pixels until running for few hours. Also had a dead HDD with a lot of hours. So I thought changing to a lower age LED bar is probably good for longevity.

 

[howardc64]

Attempted to remove the LED. Did not succeed. LEDs are probably glued down.

• 450C hot air from under the LED bar
• Flux, added some leaded solder
• Tried heating from top directly over LED

Doesn't come off. Probably glued down under the LED chip. So entire LED bar replacement is probably necessary

 

[woutnme]

If are with glue and cant remove with hot air, or a iron plate under, can try with a nail grinder with care, stop when you see plated legs and can remove with iron hand welder.
That cant fail.

 

[howardc64]

If are with glue and cant remove with hot air, or a iron plate under, can try with a nail grinder with care, stop when you see plated legs and can remove with iron hand welder.
That cant fail.

Yes, that'd probably get it off but can't extract a good donor LED destructively.

 

[woutnme]

OHH you want only replace the led from the other? its cheaper remove and replace only the led with a new one.
Can check the VF and current, see a similar color and buy only the chip led. Maybe on internet found the chip led compatible...
The best way its replace the complete bar if are a paid job, for warranty... the customer dont will understand when broken again you want make it cheaper for him interest...
Good luck!