Third display not recognized by MacPro

Question

Third display not recognized by MacPro

I currently have 2 Dell monitors hooked up via display port adapters to two thunderbolt ports on the back of the MacPro. I just purchased a 3rd external TV monitor to use for previewing edits and connected it to the HDMI port on the back of the MacPro. It isn't recognized by the system as another display. I also tried a third thunderbolt > hdmi adapter that I had, with no luck.

When I remove one of my two monitors the HDMI port appears to be active and I get the extended desktop on the TV. Plugging back in the monitor doesn't bring that monitor back. I have to first unplug the HDMI, and then plug the monitor to get my dual configuration to return.

Very surprised by this, as my expectation was I can run 3 4k displays at once on this. I'm hardly pushing the limit with two 20" Dell 2007FP's and one external TV.

Any thoughts on why this is happening and how to resolve?

Thanks

Steve

Mac Pro, OS X Mavericks (10.9.4), 32GB RAM, 3.5Ghz 6-Core, Dual D500

Posted on Jan 16, 2015 11:43 AM

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Answer 1

The hatter

Level 9

61,031 points

Jan 16, 2015 11:49 AM in response to Stephen Barrante

This is the FAQ:

Thunderbolt ports and displays: Frequently asked questions (FAQ) - Apple Support

Using 4K displays and Ultra HD TVs with Mac computers - Apple Support

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Answer 2

lllaass

Level 10

210,519 points

Jan 16, 2015 12:31 PM in response to Stephen Barrante

I think you are running into bold italics:

Can I connect a DVI display?

Mac Pro supports DVI displays using Mini DisplayPort to DVI adapters. Use a single-link DVI adapter such as the Apple Mini DisplayPort to DVI adapter for DVI displays with a resolution up to 1920x1200. Use a Dual-Link DVI adapter such as the Apple Mini DisplayPort to Dual-Link DVI adapter for resolutions up to 2560x1600.

Mac Pro supports a total of two single-link DVI displays. If you connect a third DVI display using a passive adapter or a display via HDMI, it will cause one of the three displays to become inactive.

Can I connect more than 2 DVI or HDMI displays?

Mac Pro supports a total of two DVI or HDMI displays when connected via the built-in HDMI port or using the Apple Mini DisplayPort to DVI adapter. To connect additional DVI displays, use an active DVI adapter such as the Apple Mini DisplayPort to Dual-Link DVI adapter. You can connect up to six active adapter DVI displays. This requires a powered USB hub since Mac Pro offers four USB ports and you will need six to connect them all.

Which displays are active during startup?

Usually only one connected display will illuminate until OS X is finished starting.

From:

Mac Pro (Late 2013): Using multiple displays - Apple Support

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Answer 3

Jan 16, 2015 1:00 PM in response to lllaass

So... because I am using the two Mini Display Port adapters to go to each DVI cable / monitor, adding the HDMI is not supported?

And if I understand this correctly, In order for this to work my monitors would need to each have HDMI inputs so I only have to go from Thunderbolt to HDMI, without an adapters and then my 3rd monitor will work if I use the HDMI port...?

I think it's ridiculous that I'd have to use an active adapter to run 20" monitors, and tie up my USB ports on top of it. Maybe I can get away with only one...

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Answer 4

Jan 16, 2015 1:08 PM in response to Stephen Barrante

You do not need the very expensive (US$100) ACTIVE Dual Link Adapter, provided display width is under 1920 wide. Third party ACTIVE adapters from Mini DisplayPort (plugs into ThunderBolt) to Single-Link DVI are available for under US$35, and use the power from the interface (no USB needed).

Graphics card makers now talk about DVI and HDMI as "legacy" display interfaces. That sure makes me feel OLD.

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Answer 5

lllaass

Level 10

210,519 points

Jan 16, 2015 1:10 PM in response to Stephen Barrante

If the monitor is not greater than 1080p then you do not need the expensive dual-link adopter. You do however need an active mini displyaport to DVI adopter like:

http://www.startech.com/AV/Displayport-Converters/Mini-DisplayPort-to-DVI-Active -Adapter~MDP2DVIS

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Answer 6

Jan 16, 2015 1:12 PM in response to Grant Bennet-Alder

Thanks for the insight everyone.

Grant - the 3rd display has just the HDMI in, as it's a TV, so I guess I'm confused why the HDMI to HDMI isn't working. My other two displays are using the Single-Link Mini DisplayPort adapters. All displays are under 1920.

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Answer 7

Jan 16, 2015 1:15 PM in response to lllaass

Sorry - overlapping some responses here.

I'm currently using two http://www.amazon.com/gp/product/B007KB0EGC/ref=oh_aui_search_detailpage?ie=UTF8 &psc=1

So, Illaass you are saying that those are not the same as the adapter you listed? Also wondering if I do need to get the different adapter, can I get away with just using one? Rational, I'm "fixing" whatever issue was caused by adding the second display, so I can then support one additional display... make sense?

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Answer 8

lllaass

Level 10

210,519 points

Jan 16, 2015 1:19 PM in response to Stephen Barrante

Because you can on have two legacy (DVI or HDMI) monitors conected with simple, non-active adopters or straight HDMI connection. Plug the TV into the HDMI port of Mac and purchase an active mini displayport to DVI adopter and use one of your non-active mini displayport to DVI adopter

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Answer 9

lllaass

Level 10

210,519 points

Jan 16, 2015 1:22 PM in response to Stephen Barrante

The standard, run of the mill mini displayport to DVI adopter are not active. Did the package/description say active? Active ones cost more.

Stephen Barrante wrote:

Sorry - overlapping some responses here.

I'm currently using two http://www.amazon.com/gp/product/B007KB0EGC/ref=oh_aui_search_detailpage?ie=UTF8 &psc=1

So, Illaass you are saying that those are not the same as the adapter you listed? Also wondering if I do need to get the different adapter, can I get away with just using one? Rational, I'm "fixing" whatever issue was caused by adding the second display, so I can then support one additional display... make sense?

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Answer 10

Jan 16, 2015 1:25 PM in response to Stephen Barrante

These are recommended as well:

http://www.amazon.com/Accell-B087B-006B-2-DisplayPort-Single-Link-Certified/dp/B 0098HVZA0/ref=sr_1_3?ie=UTF8&qid=1421443353&sr=8-3&keywords=ACTIVE+DVI

to do the job, it needs to be sold as ACTIVE.

There are others available, but the Startech and Accell are recommended by AMD/ATI.

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Answer 11

Jan 16, 2015 1:33 PM in response to Grant Bennet-Alder

Thanks guys!

Not to get off topic, but out of curiosity does this only affect the ability of these ports to be used for display purposes? I have several Thunderbolt RAIDs connected (and distributed via different Bus's) and wondering if I should expect a drop in read/write speeds.

Best

Stephen

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Answer 12

Jan 16, 2015 1:47 PM in response to Stephen Barrante

Only affects conversion to "Legacy" Display interfaces, such as DVI. Mini DisplayPort (subset of ThunderBolt) uses lower Voltage and less power, so when you convert more than one to something (like DVI) that requires more power, you need an ACTIVE adapter to boost the levels up.

Not ThunderBolt stuff at all.

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Answer 13

Jan 16, 2015 1:51 PM in response to Grant Bennet-Alder

Thanks Grant, really appreciate it.

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