How do I adjust the brightness of a Thunderbolt display?

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Level 1

5 points

How do I adjust the brightness of a Thunderbolt display?

I have a 27-inch iMac running El Capitan and a 27-inch Thunderbolt monitor as a second display. I can't find a way to adjust the brightness of the Thunderbolt display so that it matches the brightness of my iMac display. I've tried through system preferences, but there is not provision for doing this. I've tried setting the Thunderbolt display as the primary monitor and that didn't work. I've also tried various combinations of pressing the control key and F1 and F2, option key with F1 and F2, command key and F1 and F2, etc. None of these seem to affect the brightness level of the thunderbolt display. Does anybody know how do do this?

iMac 27″, OS X 10.11

Posted on Sep 21, 2022 02:30 PM

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Answer 1

Sep 23, 2022 05:36 PM in response to Skylark83

<< USB ports on the display not working >>

that's why you can't adjust the brightness.

Apple has been chatting with its displays about setting across USB for many years. Much older displays lost their brightness slider when the USB was not connected. And no brightness slider means the keyboard keys can not work.

Does the display have external buttons?

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Answer 2

Skylark83 Author

Level 1

5 points

Sep 23, 2022 10:45 AM in response to Grant Bennet-Alder

Yes, absolutely, this is regarding a second display that is an Apple Thunderbolt 27-inch display., connected via the built-in display port cable.

My iMac is a late 2013, 3.5GHz i7 with 32GB of DDR3 memory and NVIDIA GeForce GTX 775M graphics card. I'm running El Capitan, v. 10.11.6 on it. I can't upgrade this machine's OS because I'm running a bunch of older software on it that won't run on a newer OS.

Even if I set the system preferences to mirror both display, changing the brightness for the iMac does not affect the other Apple monitor. Here's the hardware info from the system hardware summary:

Thunderbolt Display:

Vendor Name: Apple Inc.

Device Name: Thunderbolt Display

Vendor ID: 0x1

Device ID: 0x8002

Device Revision: 0x1

UID: 0x000100010022D8B0

Route String: 1

Firmware Version: 26.2

Port (Upstream):

Status: Device connected

Link Status: 0x2

Speed: Up to 10 Gb/s x2

Port Micro Firmware Version: 2.0.7

Cable Firmware Version: 0.1.18

and the graphics card info:

NVIDIA GeForce GTX 775M:

Chipset Model: NVIDIA GeForce GTX 775M

Type: GPU

Bus: PCIe

PCIe Lane Width: x16

VRAM (Total): 2048 MB

Vendor: NVIDIA (0x10de)

Device ID: 0x119d

Revision ID: 0x00a2

ROM Revision: 3782

Displays:

iMac:

Display Type: LCD

Resolution: 2560 x 1440

Pixel Depth: 32-Bit Color (ARGB8888)

Main Display: Yes

Mirror: Off

Online: Yes

Built-In: Yes

Thunderbolt Display:

Display Type: LCD

Resolution: 2560 x 1440

Pixel Depth: 32-Bit Color (ARGB8888)

Display Serial Number:

Mirror: Off

Online: Yes

Rotation: Supported

Connection Type: DisplayPort

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Answer 3

Skylark83 Author

Level 1

5 points

Sep 23, 2022 01:29 PM in response to Grant Bennet-Alder

Yes, it is plugged in directly into the iMac Thunderbolt port.

Funny you should ask about the ports. The USB ports on the back of the Thunderbolt display mysteriously stopped working about a year ago. One day they worked and the next day they didn't. I've called Apple about this several times and they couldn't help me. I've tried the basics like powering everything off, unplugging everything for a while, resetting pram, but none of those had any affect. So none of the USB ports on the back of the Thunderbolt display are currently working. This is a shame, because I used those ports all the time and it was one of the reasons I really liked the display. I haven't tried the fire wire ports recently so I'm not sure about them.

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Answer 4

Skylark83 Author

Level 1

5 points

Sep 24, 2022 02:12 PM in response to Grant Bennet-Alder

No, there are no external buttons on the display and I never connected the Thunderbolt display to the iMac with a USB cable. It has always been connected to the Thunderbolt port on the iMac via the cable built into the Thunderbolt display.

I only used the USB ports for connecting external drives, iPhone, iPod, SD card readers and things like that. The calibration and brightness of the display is supposed to be adjustable from the Mac OS system preferences and it used to work that way originally, but for some reason this method no longer works.

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Answer 5

Sep 24, 2022 02:43 PM in response to Skylark83

USB is included inside the Thunderbolt connection into the display, and splits off in a ThunderBolt Hub inside the display. So it does not need a separate USB connection on the Thunderbolt Display.

On the very similar Mini DisplayPort version of this display, there is a separate USB cord, and it must be plugged in to get Brightness to work.

One possible thing to try is to 'give the display a Timeout' -- make it sit in the corner with no data and no AC power cord at all for a quarter hour. See if it does a deep reset and its ThunderBolt Hub starts working properly again.

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