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27" display with 2560 x 1440 pixels resolution Thunderbolt & MagSafe cable attachments

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Backlight for thunderbolt display failing at full power

Just bought an Apple Thunderbolt display off Craigslist, 27” (A1407 2011 model). The backlighting on the display bugs out when it’s at full brightness (as far as I can tell, the display works as intended at half brightness). I got a deal on it - so I’m mainly wondering if it’s something simple that I can repair, or if I should try to run down the person I got it from for a refund?

As I increase brightness to much beyond halfway, a few things happen:

  1. A slight buzz sound. The volume increasing proportionate to the brightness.
  2. Intermittently flickers (less than 1 second going totally black, then back immediately) 3 - After a few minutes, it goes completely black (it’s just the backlighting for the LCD, it’s still connected, and if I shine a flashlight on the screen and move something, I can barely make out a dim existence of a non-backlit display).
  3. Unplugging the monitor from thunderbolt does nothing, only unplugging from power and then plugging back in will get the backlight to come back.

Things I’ve tried:

  • Cycling power to devices
  • Software updates (  Port Micro Firmware Version: 2.0.7, and Firmware Version: 26.2)
  • Multiple different machines with and without uSB-c adapter
  • Different thunderbolt cable (vs the built-in one)
  • No other devices are plugged in besides power and thunderbolt.
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@danj and @oldturkey03 – you've both had great thoughts on similar problems would love your thoughts.

Maybe this one is related too? Brightness can be set only on low setting

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There is only two parts involved with the backlight: the logic board which is has the MOSFETs & inductors which controls the three backlight strings and the display assembly its self which has the backlight LED’s.

Your symptoms implies the LED driver logic is messed up on the logic board. If you want to try to fix the driver logic you’ll need to grab the schematics - board: 820-2997 drawing: 051-8774

Or just replace the logic board: 27" Thunderbolt Display Logic Board, Apple P/N 661-6060

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Awesome - do you have any indication that the problem has the probability of getting worse? I can live with it at a lower brightness, but probably want to fix/return if it's going to start blacking out at a lower brightness in soon.

Also there were some indications in other answers that buzzing because of brightness volumes were an indication of power supply issues - do you think that's a possibility?

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Coils buzz! You have three on the logic board (inductors) and you have a few coils within the power supply. Basically, either could be the source! Given the backlight its more likely the logic board inductors.

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Stevens sera éternellement reconnaissant.
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