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

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Replaced the PSU, Logic Board and Cable - Still disconnecting

Hi

My Apple 27” Thunderbolt display started disconnecting and the screen would blackout.

I’ve replaced the TB/Magsafe cable, the power supply, and the logic board. The screen is able to show an image - but only for a few seconds before going black again. If I unplug the cable from my mac and immediately plug it in again, the image does not come back. But if I wait 5-10 minutes and plug it in again, the image show up briefly before the screen goes black again.

In “System Report” there is nothing connected to the thunderbolt port when the screen is black. So it’s not detecting the logic board I assume.

The MagSafe is able to charge my Macbook Pro so I do not suspect the EMI filter is cutting out, as the PSU would have no power or at least intermitting power. The charge light is solid.

Can it be the backlight of the LCD panel itself that is broken? It is able to light up, so maybe some driver circuitry? The reason I am not sure is, when the display goes black, MacOS blinks like the screen is physically disconnecting. To my understand, the backlight driver is “dumb”. It would not cause the thunderbolt connection to drop.

I’ve tested with three different Macbooks.

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Well, you’ve almost shown the kitchen sink at it!

Sadly, I’m suspecting the backlight within the display or the thermal sensor within the T-CON is failing. If you have a spare display you could try swapping it out.

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Hi

Thanks for taking your time to answer.

I've replaced the logic board, so I guess it cannot be the T-CON?

Here's a short video: https://imgur.com/a/ZTPv7mu

As you might be able to tell, the Thunderbolt bus says "No device connected" for both ports. Even when the picture on the screen is showing. Not sure if this is because the screen is not connected long enough for the system to update or if this is related to the computer not detecting the screen properly.

Wouldn't my computer still be able to recognize the screen is connected via Thunderbolt even though the backlight is not working? Or will a faulty backlight provide feedback to the logic board telling it not to present itself to the computer connected?

Edit: found out you have to refresh the "System Profile". I was able to catch the display connected. https://imgur.com/a/MgRaQVl. After five seconds the screen went black and it was being detected anymore. This leads me to think it has something to do with the logic board.

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@kgeeee - The T-CON is the logic board in the display assembly (where the display cable connects to). If the T-Con sensor signals the display is too hot it will shut the display down so you wouldn't see it as a viable display.

27" iMac LCD TCON Controller Board - SD E3 This might work or at least offer you the needed parts to fix yours.

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@danj Yeah, that could likely be the culprit. But would it cause the screen not to be detected via Thunderbolt?

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@kgeeee - Yes, added some more info

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@danj Thanks, again. It seems this is for the 27" iMac.

It does seems the T-CON is not the same for the iMac and Thunderbolt display if I read this correctly: Can I swap a LCD from a 27" 2009 iMac into a 27" thunderbolt display?

Also it seems there is no T-CON available for sale at the same site:

https://www.thebookyard.com/parts-apple-...

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