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

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Apple Thunderbolt Display backlight issue?

Hi Team,

I'm hoping someone can help me with the issue with my thunderbolt display.

Here is whats happening

When I plug it in initially the screen will light up normally. Then after a period anytime from a few seconds to a couple of hours it will go black.

things to note:

-Everything plugged in to the display still works; webcam, usb ports, cooling fans etc.

-I can see the monitor from the system report and the latest firmware is present (26.2)

-I can see a faint outline of my desktop on my darkened screen if I hold a light up to it

I have taken it to an apple repair shop and after a cursory look they identified the logic board to be at fault. they have quoted $350 to replace it. A bit too much to spend on an old screen.

I have looked at reflowing the board in the oven or under a heat gun (hey what have I got to loose right?!) but there are lots of plastic parts and I think I might do more damage than good.

Maybe someone might have a better idea?

Please help

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@danj you have commented on a couple of these issues

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Thank you @danj & @oldturkey03! I'm reaching the extent of my expertise. I can pull apart the components but I'm a bit lost when it comes to DVM measurements and even finding the fuse for the screen. I have uploaded a couple of photos of the logic board

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Thank you. I should mention I'm in Australia. I'm hoping to try something to repair the board before replacing it

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@alexreid Paul Daniels can help you at Charter Towers Phone and Computer Repairs

http://ctpc.biz/

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3 Answers

Chosen Solution

@alexreid a reflow probably will not work since you have images just not a backlight. I'd start by checking things like C1100 to see if you have 3.3V going to your backlight enable circuitry etc. (also possibly a backlight fuse) to see what the power situation is on that one. Post some good images of your board with your question so we can see what you see. Use this guide Adding images to an existing question for that. We might identify the components in question. Check things like step 12 of this teardown Apple Thunderbolt Display Teardown it shows your LED driver (HV9982) in the black square.

Apple Thunderbolt Display Image

Guide

Apple Thunderbolt Display Teardown

Difficulty:

Moderate

iFixit Image

Guide

Adding images to an existing question

Difficulty:

Very easy

2 - 5 minutes

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@oldturkey03 I've added a couple of images of the logic board. Visually I can't see anything wrong with LED driver. There are however a couple of suspect components with a chalky white residue on the back of the board near the solder points

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@alexreid that area looks like it did get hot. Does not look like dust. This repair would require using schematics and micro soldering experiences etc. You can see if anybody like @reecee or @tcrs_circuit can provide you with more help in that aspect. Otherwise the only real option you would have is to replace the board.

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Surprisingly this is an easy fix for someone who has micro soldering skills and access to the SMT parts.

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Hmmmm and you elaborate? which part?

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You'll need to get your hands on the schematics and board layout drawings and know how to use a DVM to measure the voltages.

Review the IFIXIT teardown Apple Thunderbolt Display Teardown Steps 11 & 12. Check the Supertex switch-mode LED driver. Given the fact the screen winks out I'm suspecting one of the caps is bad or you have a cold solder joint.

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So would you suggest trying to reflow that chip with a heat gun first? or taking it to someone and trying to replace it?

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You really need to properly diagnose using a DVM and measure the voltages.

As OldTurkey stated the issue is more likely a failing capacitor which I agree,

Reflowing the chip is not what I was thinking, Its more an issue of replacing. This chip often fails. but you need to check it before you replace.

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DO NOT heatgun that!!!! You will risk ruining it.

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I'm not sure what else you can do, but this is a source for the part although it is currently out of stock. https://beetstech.com/product/thunderbol...

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Alex Reid will be eternally grateful.
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