Deep in the weeds with this THUNDERBOLT 27" display -I have no screen, and the thunderbolt connection not detected by an external computer, but power is getting to the logic board just fine. Tested the G, 12V, and 24V rails and power is fine on the logic board. When testing the smaller panel test points, fan, usb, etc. works great, but no power at the LCD power panel test points (Just to the left of the circled component in the pic attached). There should be 12v there according to the Technician's manual.

Ok, but there IS 12V right at the circled component on the one leg at the bottom, but 0 volts on either of the other two legs! So I suspect this part has failed.

Now the help! What is this part? Voltage divider or detector? It's labeled with either a "AM K" or "1 AM K" (K is sideways) although the 1 might just be a line indicating directionality? These components are all over the board and always gives voltage readings on all legs, so that's why I suspect this one is bad. Any super smart SMD folks know what this part is?

⟐ Commented January 21, 2026 at 18:21 MST

Thunderbolt Display connected to Mac mini 2018 MacOs 10.15.6 via Thunderbolt adapter to USB-C.

I’m skeptical of the display because no issues to TV but that’s HDMI signal not Thunderbolt. I’ve repaired the A1267 and hoping not to mess with this one.

#2-How hot is too hot for this display? Fan is running.

#3-Should Display USB ports always have constant power when Mac is off? Will not charge phone constanlty

Thanks in advance..

What’s supposed to be connected here?

No extra parts found

⟐ Commented January 10, 2026 at 11:38 MST

Symptoms

• The display shuts off randomly, but more frequently when my MacBook (late-2012 Retina) is closed.
• When closed: The display cuts out every 1–2 minutes or less.
• When open: It lasts 2–5 minutes before cutting out.
• If it cuts out while closed, the MacBook screen stays off until I unplug the display.
• If it cuts out while open, the MacBook screen remains on like normal.
• Moving the MacBook away from directly under the display significantly reduces the issue.
• Speakers will continue playing music, peripherals continue charging or maintain connection, macbook remains charging from the TB cable. No interruption when the display cuts.

Troubleshooting

• Checked, unplugged, and cleaned all cable connections.
• Updated my OpenCore Legacy Patcher (OCLP) build and patches.
• Reset NVRAM/PRAM—but I didn’t hear the Thunderbolt Display fan cycle.
• Noticed the display feels warm.

This makes me wonder if it’s heat-related. Since the issue improves when I move my MacBook away, I’m thinking the Thunderbolt Display’s cooling system might be failing or the heat from the MacBook is affecting it.

Does anyone have insights or similar experiences? Any suggestions on what to check next?

I've been waiting for a new thunderbolt m-to-m cable, it finally arrived. I plug it in and get nothing, the strange thing is one or two of the times that I attempted connected, the screen on both the mbpr and tb display flashed like it connected but then cut immediately back to mbpr.

The display fires up and works normal with the factory octopus power/tb cable (other than the intermittent cutting issue of course)

I'm lost. Is this new cable bad? I dont have any other TB2 devices to test this.

⟐ Commented November 16, 2025 at 12:16 MST

Strangely, even though when the video is not working, my MacBook still recognizes it (in the sense that I can select screen arrangement settings in System Preferences and also move my mouse onto the other screen). Furthermore, the speakers and camera still work when the screen is black.

I have tried resetting PRAM/SMC and tested multiple laptops and the problem persists. I have also tried using an external thunderbolt cable. Finally, I have shined a light on the display when it is dark and I can’t see any faint images.

Two things that sometimes work to “revive” the display are plugging the AC power cable into another outlet or unplugging the AC power cord where it connects to the back of the display and then plugging it back in. I have also noticed that if I accidentally bump the AC cable where it plugs into the back of the display, this can cause the screen to go black.

What is the likely culprit here? I suspect the AC power cable, but perhaps it is a logic board issue? Additionally, if the AC power cable is at fault, where can I find the right model? I don’t want to buy the wrong one by accident and I also want to make sure I buy from a reputable seller.

⟐ Answered July 08, 2025 at 13:49 MST

I don't have any troubleshooting tools but the USB port provides power to devices momentarily on plugging it into power then it does not.

Trying to get money back from seller but hopefully I can diagnose and correct beforehand.

Edit: power is being supplied from the charging cable to an old macbook. While this is charging the macbook, the usb appears to be getting intermittent power. I have an iphone pluuged into the USB and it will charge and uncharge by itself.

Thank you!

⟐ Commented January 18, 2025 at 6:33 MST

Edit: I have bought an A1312 iMac stand and it seems to fit fine. It’s about 9cm from the desk to the bottom of the display so if any other Thunderbolt Display owners would mind measuring to see if they are the same or not that would be awesome. Here are some pics of it all mounted up.

⟐ Edited by author January 10, 2025 at 23:21 MST

So far, I've tried cleaning the contacts with rubbing alcohol. This made them more visually attractive, but did not solve the problem.

Second, I tried using another macbook pro, but it had the same issue.

I've noticed that the thunderbolt connector heats up significantly when it's in use. I'm wondering if there's a heat-related issue that could be causing a broken connection in the electronics inside the connector. Any thoughts?

⟐ Commented January 06, 2025 at 8:33 MST

@danj Thanks Dan, mine is different. Look at the photo, I marked what seems to originate the bad smell. Is still the component you mentioned before?

⟐ Commented October 22, 2024 at 19:09 MST

recently, I put my MacBook Pro (2015) on my Thunderbolt Display to charge it up, as I always do. When I came back to it after a few hours, I noticed that it stopped charging, the laptop was around 60%. I tried re-connecting the MagSafe from the Thunderbolt Display and powered it off for a few minutes, but it didn't help - it seems that it won't charge any MacBooks anymore... The display functions normally otherwise, even though it makes a clicky noise when the brightness is at the maximum. It's very silent, but noticeable.

I did some research if this is a common problem, the only thing I found was that its sometimes the MagSafe converters that fail after some time. This is not the case for me, I connected an old MacBook (where the converter isn't needed to charge it) and got the same result - no charging.

The cable coming off the display is in pristine condition, no splits or fraying (yet), so replacing that probably won't solve my problem. The normal power adapter that came with my laptop still functions flawlessly.

My question would be if this happened to any of you as well and how could you fix this? Could this point to a defective logic board? Is it possible to have that repaired or should I get the whole board replaced?

Your help is very much appreciated!

UPDATE: See below what coconut battery indicates, in the bottom I specify the case.

⟐ Answer edited May 10, 2024 at 16:38 MST

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

⟐ Answered April 22, 2024 at 2:55 MST

When it doesn’t. The display is not recognised by the Mac. The MagSafe gives power (although not very much).

What are the troubleshooting steps from here?

(I took it to the local repair shop who charged me €20 for diagnosis and gave it back saying they couldn’t get it apart but it “doesn’t work” :-)

⟐ Answer accepted February 04, 2024 at 14:23 MST

Can this be fixed

⟐ Answered December 08, 2023 at 16:10 MST

⟐ Commented November 21, 2023 at 7:49 MST

I was given the task of fixing a Thunderbolt display at my university. If I can fix it, I get to keep it, so I accepted the challenge. First impressions of this display weren't too bad. The issue that it has however, is that when plugged in, all over the screen is a bunch of horizontal lines. I was told before testing it that when it was last powered on, there were only sections of the display that had lines, but I'm not certain if that was describing the same defect I was seeing on the display.

Either way, everything else seemed to work perfectly fine, so today I partially disassembled everything to see if there was anything clearly wrong. I can't remember if someone has already tried working on this unit before, but it looked very tidy. Everything looks intact, and visually the power supply and logic board looked good.

So, I'm not so sure where to start, I just know my issue may lie in either the logic board or the panel itself. I'm inclined to say the panel is flaky given the other issues I've seen here.

If anyone has any insight as to what I should try to do to troubleshoot, it would be greatly appreciated!!

⟐ Commented November 04, 2023 at 19:24 MST

Thanks for advise!

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?

⟐ Answered October 29, 2023 at 17:14 MST

THIS IS EXAMPLE

⟐ Answered October 16, 2023 at 15:53 MST

Today my thunderbolt display suddenly went very dim. I've tried turning it off and then back on again but it doesn't work. I tried to adjust the brigtness on the Macbook pro, when I moved the slider, sometimes the screen brightened and then went dark again.

Still unsure is this about the connection cable or the backlight.

Have any idea about this anyone?

https://youtube.com/shorts/hyUcPAxfNc8?s...

⟐ Answer accepted October 07, 2023 at 7:07 MST

A friend have a problem with his 27" Thunderbolt display. Is it really annoying buzzing sound. My first guess would be the power supply??

The display in functioning OK, but that noise is killing the entire office.

How is the front glass attached? Glue? Can't see that in the break down guide.

Anyone else seen this?

Thanks

Here is a video of the issue.

YOUTUBE Video

⟐ Commented September 25, 2023 at 15:41 MST

So, what could be wrong with this display? Any thoughts?

Thanks,

⟐ Answer accepted September 23, 2023 at 8:18 MST

⟐ Commented August 12, 2023 at 9:52 MST