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

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How to diagnose thunderbolt display?

Got my thunderbolt display completely black, nothing shows up on screen, no sound from speaker, no iCam, and it won’t charge my Macbook Pro laptop either (the charging light is not on at all). Is there a way to diagnose which component failed, PSU, logic board or thunderbolt cable itself?

Thanks for advise!

Update (11/03/2021)

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Hi Dan, here are the pictures I just took, the TB cable looks good physically. Unfortunately, I don’t have the separate TB a as available, but I can buy one if it is necessary. So, if I get the images showing up with the separate TB cable, does it mean the internal TB cable is bad? And if no images with that separate TB connected, which means the logic board is bad?

Отвечено! Посмотреть ответ У меня та же проблема

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I'm scared to think that this entire discussion took place in 2021 when just getting another Apple TB display can go for $100 off any secondhand market. Was the time spent here harassing Dan (who has nothing to do apparently) worth it? Let's assume you earn $100 in at least 4 hours working, which is way more than you committed to this post, how is this a justifiable use of time?


@applepoor - Its called COVID ;-{

FYI - A used display runs from $200 ~ 500 USD


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Well from your symptoms your power supply has failed.

If you had a USB Mini Voltmeter you should see the 5volts on the USB ports which is likely not present here. Opening the display you could also test the voltages the 120 AC entering and the power feeds to the logic board and MagSafe cable.

27" Thunderbolt Display Power Supply - 250W, Apple P/N 661-6048

USB Mini Voltmeter Изображение


USB Mini Voltmeter


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Thanks Dan, so, in order to do that test, I need to have the power cable connected to the wall plug, and insert that USB Mini Voltmeter into one of the usb ports at the back, right? And also, do you have instructions how to test that voltages the 120 AC entering the power?


@lovecd - Yes! That's the easiest go - no go test you can do with the USB meter.

And yes, thats with the system plugged in to AC and press the power button the meter should react if the issue is something other than a power supply. If not it's the power supply.

If you are not comfortable with using a DVM meter and probes testing 120 voltages, its best not to risk it as you could get hurt.

This is after you've properly opened the system (unplugged) and then probe the power supply directly after you plug the system back in. This is to check if the socket is bad vs the power supply as that could also be bad.


@danj - Thanks Dan, will try that.


@danj - Hi Dan, here is the update, got the USB multimeter from local store and have it connected with thunderbolt display, surprisingly, it does show 5V on all USB ports there, and I can hear some sound from the PSU area after the connection with multimeter, does this mean the PSU is still good, and the issue will be either logic board or thunderbolt cable?

P.S, it still can not power on the macbook pro on the charging port.

Any thoughts?


@lovecd - That sounds encouraging! OK What does the TB and MagSafe cables look like are they damaged in any way? Post a few pics if that helps Adding images to an existing question

Do you have a regular TB cable? If you do plug it in one of the back ports of the display and then plug in the other end into your iMac or Mac Pro system. That will work as a connection! Did that work?


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Tom будет вечно благодарен.
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