KVM for 2x Apple LED Cinema Displays

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Level 1

15 points

KVM for 2x Apple LED Cinema Displays

I am trying to find a KVM that will work with my 2 Apple 27" LED Cinema Displays (not the thunderbolt ones) and am having no luck. I have bought 2 KVMs and dozens of mDP to DP adapters and none show a picture on either display.

I am using an Apple Mac Pro 6,1 and a PC and want to share the 2 displays between them.

If I connect the 2 displays to either computer it works perfectly. If i connect both computers to the KVM with 2 Samsung DP displays it works perfect. I don't understand why the Apple displays don't work.

Both computers do have a TB2 port if needed.

I considered using 2x Apple TB2 to TB3 adapters to connect the 2 computers to a TB3 KVM and the 2 displays with 2x mDP to USB-C adapters to the KVM or a TB3 dock with 2x DP outputs but wasn't sure if that would work and would be a very expensive option.

Do I need a KVM with EDID emulation?

Would converting the mDP of the displays to HDMI with an active adapter and using a HDMI KVM be a better option? If so how would i convert the HDMI back to DP for the 2 computers? Each computer does have 1 HDMI port if that helps.

Posted on Jun 24, 2025 01:17 AM

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Answer 1

Jun 24, 2025 07:00 AM in response to Peter Jason

Cinema display LED 27-in A1316 from 2011 is a 2560 by 1440 display that features lead-in cord with three connectors -- Mini DisplayPort, MagSafe-2 and a USB-A pigtail. It does NOT work with the Thunderbolt adapter, but works fine with a USB-C to miniDisplayPort adapter.

It includes three USB 2.0 ports and a convenient single cable with THREE connectors (Mini DisplayPort, MagSafe-2, and USB 2.0), a built-in iSight camera with a mic and a 2.1 speaker system.

These displays do NOT work with the ThunderBolt-2 <-> Thunderbolt-3 adapter, because they are not ThunderBolt displays.

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Answer 2

Jun 24, 2025 07:00 AM in response to Grant Bennet-Alder

DisplayPort cables are limited in LENGTH. Unless your KVM re-drives the signals, you need the total cable length to be ONE meter or less to avoid signals degrading and the displays dropping out. The Mac is very sensitive to this, especially in more modern MacOS.

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Answer 3

Peter Jason Author

Level 1

15 points

Jun 28, 2025 07:23 PM in response to Grant Bennet-Alder

It works fine with any of my other displays I have just not the apple ones, both the PC and Mac Pro work fine with the KVM I just cannot get the Apple Displays to show anything. I tried using a mDP to DP adapter as well as a mDP to DP 1M cable, both do not work. If i plug the displays into my TB2 dock or the TB2 to TB3 adapter they do in fact work fine, they also work fine with the mDP to DP adapters and mDP to DP 1M cables directly to the PC.

Also as stated in first post I wasn't suggesting to use TB adapters if you read it correctly. I was asking if I used a TB KVM connected to the PC and Mac Pro via TB and the 2x Apple displays to the KVM via DP would it make a difference. Nowhere did I say connect the displays to a TB port. Anyhow I still have yet to find any KVMs that support the Apple displays including the 24" LED ones so I may just rip the guts out of them and put new LCD driver boards in them and be done with it but its a huge undertaking.

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Answer 4

Peter Jason Author

Level 1

15 points

Jun 28, 2025 07:34 PM in response to Peter Jason

As for this myth about Macs not working with DP cables over 1M thats false, I have been using 2x Samsung DP displays on the same Mac Pro for over 5 years with 2x 10M cables with not one issue.

The issue with these displays I am finding has to do with the data interconnect where the display communicates with the computer to identify itself and the computer simply not responding so the displays never turn on.I know I can inject the EDIT to the graphics card to emulate a display being connected but I can't find any info about the reverse for sending a response to the displays. Of course Apple has to make things difficult in this manor as most displays don't look for a response code in order to turn on.

I have ordered a much better KVM with smart capabilities to see if that works. It claims to have 2 way EDID emulation so perhaps it will work.

I wrote an app to control the brightness, volume and cameras of both displays from within windows as the bootcamp ones won't install on a PC. Those work fine but I am unable to get the displays to identify as Apple Displays within windows hense why i think there is an issue with the communications between computer and display.

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Answer 5

Peter Jason Author

Level 1

15 points

Jun 28, 2025 08:00 PM in response to Peter Jason

Just an update, I got a 2:1, 1:2 bidirectional DP switch and it works fine just not an ideal solution as I would need 2 of them, plus a USB switch and a method of getting all 3 devices to switch at the same time.

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Answer 6

Jun 29, 2025 01:48 PM in response to Peter Jason

<< The issue with these displays I am finding has to do with the data interconnect where the display communicates with the computer to identify itself and the computer simply not responding so the displays never turn on. >>

Right idea, but you have who tells whom Backward.

The Mac does not rely on Windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

also, a KVM that does not pass the secondary data channel can not identify the display-name or its capabilities, so that display will stay dark, and the Mac settings will never reflect its name.

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Answer 7

Peter Jason Author

Level 1

15 points

Jun 30, 2025 01:22 AM in response to Grant Bennet-Alder

I am very confused, I already stated that with 2 different displays the KVM with PC and Mac connected works correctly its only when i introduce the 2 apple displays that it does not work, I don't see how this is an issue with the "Mac" not waking up the displays as wouldn't the "PC" do it? both the PC and Mac show nothing. With 2 samsung DP displays everything works as it should with both Mac and PC identifying the displays correctly.

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Answer 8

Jun 30, 2025 07:28 AM in response to Peter Jason

<< Also as stated in first post I wasn't suggesting to use TB adapters if you read it correctly. >>

The people who are answering your questions here are NOT Apple employees. They are other users, who Volunteer their time and energy to help you in whatever way they can. Apple provides the forum software and a place to hold the discussion, but most Apple employees are prohibited from posting here.

Sometimes you might get information that is tangential to you wanted to know, or WAY more information than you wanted. In some cases, this information is added deliberately to provide a more complete answer to similar questions of other users who may find this discussion by searching.

PLEASE try to be gracious in your responses. If you got more than you wanted to hear, Please do not assault the person who gave you tangential or ‘too much' information. Instead, understand that they were TRYING to be helpful, even if their answer did not line up perfectly with your query.

Just ignore the overage and get on with solving your problems, and count your blessings that someone was willing to make suggestions that MIGHT be helpful, even if the answer was "too much" or “way off base”.

If important parts of your question did not get answered, just ask a more pointed question and Readers will try again.

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Answer 9

Peter Jason Author

Level 1

15 points

Jun 30, 2025 10:14 PM in response to Peter Jason

The displayport switcher method is working fine and i don't understand why its makes a difference compared to a KVM. To use the switch method i need 2 of the DP switches and a USB switch as well. I would need to press 3 seperat buttons to get it to work and much more cable mess. There must be a way to use Apple displays with a KVM i just hav yet to figure out how.

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Answer 10

Peter Jason Author

Level 1

15 points

Jun 30, 2025 10:11 PM in response to Grant Bennet-Alder

I apologize. I didn't mean to come off that way. I am just frustrated and don't understand what's happening and why an Apple display makes such a difference compared to others.

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