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

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Do the screen have a bad logic board, if it doesn’t connect?


I have bought a defective Thunderbolt screen, described as a bad PSU failure, thinking it was a bargain. I managed to replace the PSU and get power to the unit. But the screen is still black.

When connecting to my MacBook, there is power, but my MacBook cannot find the screen,

What I have tried:

I tried to use external thunderbolt cable to connecton the back of the screen.

I tried smc reset and PRAM reset.

I also tried to connect to my imac to isolate problem with thunderbolt connection on my MacBook, still nothing.

I have checked that there is power to the logicboard, with an USB stick that lights up when connected. But the strange thing I have observed, is that when I connect through the thunderbolt on the back, there is no power to the usb stick.

What I want help with:

Can the MacBook recongnise the screen even though the thunderbolt lcd is not connect?

If so then I can maybe isolate the lcd as the problem

I suspect the lcd screen, the lcd flex cable and the logicboard. But as the screen itself cannot be found, can I conclude that it most probably the logicboard?

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Whenever I encounter a blown power supply, I ask the customer if they had a power outage (surge event) or lightning strike.

What can happen is the surge or lightning strike kills the power supply and if powerful enough of the ground path is through the logic board as something is connected through it the logic board can also be damaged.

So where does that leave us? I agree you likely have a blown logic board here as we can’t ask the original owner what happened.

As for using the Thunderbolt port to connect to your MacBook/MacBook Pro depending on the exact model you may need to use a mini DisplayPort cable to test things (I’ve not tried it this way). You still need to use the attached cable as the primary connection.

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You can use the thunderbolt port from the back with an external thunderbolt cable. So if the built in is defective, no replacement is needed. I have done it before and it is also mentioned on ifixit troubleshooting. Well I have bought a used logicboard on eBay, hopefully it will fix it.



Re-read what I said ;-}

I wasn't disagreeing with you on using a TB output as an input as TB is bi-directional! The issue was needing a mDP Vs a TB cable depending on your Mac system.


Sorry Dan, I was reading too fast. And you were right I forgot that there were a times where macs used mDP.

I was going to give up un fixing the screen, but took the chance with you expertise. And luckily I did manage to fix the Screen with a used logic board. Thanks for the help Dan.


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Thien Khanh Nguyen будет вечно благодарен.
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