Problem with connecting two projectors with iMac

[turbo911]

Hello everyone,

I have a big problem, as I've been trying for past 2 weeks to figure out how to make everything work.

In church, we switched to mac 2 weeks ago and I had to connect two projectors to it, one main and the second one is upstairs projecting on back wall for choir.

I connected both projectors with DVI-D Dual Link cables, and bought DVI-D to 2xDVI-D dual link splitter and apple mini display port to DVI adapter (which is DVI-D Dual link also). I connected everything to find out I get no output on projectors. The iMac doesn't even recognize them (if I go and click Detect Screens, nothing happens).

So I disconnect one projector, while the second one (main) is still connected and a moment later I see iMac recognized it and showed extended display on projector (don't need mirrored one).

Then I try to connect second (upstairs) projector along with first one, and I get nothing, along with first one loosing the connection. I disconnect the main projector and the second one starts working. So its either one or none. Then I tried to connect main projector back and out of no where, two of them worked like no problem. So I decided to restart computer and once it was one, I get no display again. So I had to repeat same procedure again (disconnect main projector while leaving upstairs one connected and then connecting main one back) and after that I get output. But if I restart again, I get no output, no idea why.

I though it was because of the non-powered splitter, so I bough powered one and when I connected everything, turned on computer, the main projector works but the upstairs one doesn't. It doesn't say there is no signal, it got detected but it shows the same picture when you disconnect cable from TV or you have poor antenna connection. So I though that is weird, tried different resolution and nothing.

I though its because of cable length but I tested it (described below) and it wasn't that. Main projectors DVI cable length is 25ft and upstairs one is 2x50ft connected together.

So I decided to connect non-powered DVI splitter back and connected it my old PC that I had there. I turned on PC and whoala it works no problem. I tried to disconnect and connect everything again to PC and everything work no problem. So I transfer same setup back to iMac but adding mini display to DVI adapter and I get no output.

Do you guys know what could be wrong? Is it because iMac doesn't support dual displays from mini display port? I called apple, asked them and they have no idea. I don't know what else to do and out of ideas, so if you can, please help or suggest.

Thank you so much, and sorry for long read, but that was the only way to explain my problem thoroughly.

God Bless,
Slava K.

[shortcircuitcg]

For better clarification.......are you hooking both dvi ports from the Mac to the splitter?

[turbo911]

I have this splitter

monoprice.com/ products/product.asp?c_id=101&cp_id=10113&cs_id=1011304&p_id=2518&seq=1&format=2
(delete space above)

With PC it works fine.

From iMac I have mini display to DVI adapter from apple which is DVI-D dual link
From that I have that splitter listed and then to that splitter I connected two projectors.
Also I tried this splitter too but it doesn't work either with mac and with PC it works.

us.startech.com/product/ ST124DVIA-4-Port-DVI-Video-Splitter-with-Audio
(delete space in link above since it doesn't allow me to post links)

[prochlea]

I know that mac's have started using HDCP on their outputs. It could be that you need an HDCP compliant DVI Distribution Amplifier.

[turbo911]

Originally Posted by prochlea

I know that mac's have started using HDCP on their outputs. It could be that you need an HDCP compliant DVI Distribution Amplifier.

The last link that I posted, the Startech DVI splitter has DVI, and HDCP compliant for easier HD video distribution.

Thing is with PC I had no problems, but with mac I have this problem, and I can't return it because I already bought propresenter and other software for it.

[[Director] drew ryan]

What is the possibility that the projector does not recognize the DHCP?

[turbo911]

Originally Posted by drew ryan

What is the possibility that the projector does not recognize the DHCP?

What do you mean?

Also on that Startech splitter it says max distance is 30ft and I have 100ft.

Another thought is that when I connect through non-powered DVI splitter (connect upstairs projector first and then connect main one second) it works fine, but if I restart computer it won't work and I have to do same procedure again.

[zactommo]

Originally Posted by turbo911

I connected both projectors with DVI-D Dual Link cables, and bought DVI-D to 2xDVI-D dual link splitter and apple mini display port to DVI adapter (which is DVI-D Dual link also). I connected everything to find out I get no output on projectors. The iMac doesn't even recognize them (if I go and click Detect Screens, nothing happens)..

Do you have specs or a model/brand number of the splitter your using?
It is a powered splitter/amplifier or a y cable sort of thing.

Just to clarify, what is your desired result?

Do you realize the purpose of dual link DVI. Dual Link DVI means double the amount of data as single link DVI. It exists to drive ultra high resolution monitors, upto 3,840 × 2,400, such as the 30inch cinema displays. You can get 1080 on single link DVI, and dual link does not allow you to use two independent displays on a single output, it just for a single high resolution display, incase there was any confusion.

[six5tring]

100 ft... that is a seriously long way for DVI-D! I struggle to go more than 15 ft reliably (if going 1080p), 25ft at lower resolutions say 720p.

The only way I can see a 100ft run working is if the PC is talking DVI-A. Using an active DVI-D split is certainly forcing it down the D route thus at 100ft it is struggling.

Can you set the system up locally ie. bring the projectors to the DA and patch them to see what happens.

It could be an HDCP issue. I can't find information quickly googling for how many keys the iMac's support. Different sources support differing numbers of devices attached. (It's a real head ache)... using 2 projectors and a splitter the mac has to talk to 3 devices so requires 3 keys.

As I said I would put everything in the same room and short patch the lot for problem solving. This will then answer if it a cable length issue or hdcp or if you are now actually running DVI-D rather than A.

Hope that helps a little.

Ben

[turbo911]

Originally Posted by zactommo

Do you have specs or a model/brand number of the splitter your using?
It is a powered splitter/amplifier or a y cable sort of thing.

Just to clarify, what is your desired result?

Do you realize the purpose of dual link DVI. Dual Link DVI means double the amount of data as single link DVI. It exists to drive ultra high resolution monitors, upto 3,840 × 2,400, such as the 30inch cinema displays. You can get 1080 on single link DVI, and dual link does not allow you to use two independent displays on a single output, it just for a single high resolution display, incase there was any confusion.

Sorry for a lot of info, but the links were posted in the second post, but here they are again.

This is non-powered DVI-D Dual Link splitter (be sure to delete spaces since I am not allowed to post links yet)
monoprice.com/ products/product.asp?c_id=101&cp_id=10113&cs_id=1011304&p_id=2518&seq=1&format=2

Here's the powered splitter (again delete spaces)
us.startech.com/ product/ST124DVIA-4-Port-DVI-Video-Splitter-with-Audio

Our desired result is to have the same image showing on both projectors, but not using mirrored display. Basically enabling second output on iMac and having a splitter to share same output by both projectors.

Yes, I know what DVI-A, DVI-I, DVI-D (dual/single display means)

Originally Posted by six5tring

100 ft... that is a seriously long way for DVI-D! I struggle to go more than 15 ft reliably (if going 1080p), 25ft at lower resolutions say 720p.

The only way I can see a 100ft run working is if the PC is talking DVI-A. Using an active DVI-D split is certainly forcing it down the D route thus at 100ft it is struggling.

Can you set the system up locally ie. bring the projectors to the DA and patch them to see what happens.

It could be an HDCP issue. I can't find information quickly googling for how many keys the iMac's support. Different sources support differing numbers of devices attached. (It's a real head ache)... using 2 projectors and a splitter the mac has to talk to 3 devices so requires 3 keys.

As I said I would put everything in the same room and short patch the lot for problem solving. This will then answer if it a cable length issue or hdcp or if you are now actually running DVI-D rather than A.

Hope that helps a little.

Ben

Yes, I know it is a very long cable and with PC we had no issues and everything was working fine. I was able to run both projectors at 1080p through that DVI-D y splitter (non-powered one) with no problems. We have NEC NP4100 and Optoma HD72 projectors.

On a PC we had cheapest video card, Radeon X550, where iMac has Radeon HD 4670.

Yes, I know what you mean, I will try to bring the upstairs projector down and connect it there with shorter cable along with the main one to see if it is really a cable problem or HDCP.

Thank you for help, and I will let you know tomorrow, once I go back to church and try that option.

Thanks again.

[six5tring]

I still can't find the maximum hdpc limit for the mac/graphics card. The graphics card bangs on about having 2 keys per dual link but if this is all they can give your going to run into problems. 2 keys seems rather stingy!

Ben

[turbo911]

I see. I am going right now back to church to test if it is the HDCP problem or the cable length. I am also going to best buy to test there, if they let me, with an iMac and two projectors to make sure it is not adapters.

Slava