Radeon Sapphire HD 7950 problem in 2010 Mac Pro

So the stock ATI Radeon HD 5770 is a dual link?

yes, but that is not what I was trying to call out.

I'm unclear as to why the DVI(s) on the HD 7950 doesn't work though–are you saying that it's not DL?

No,

If you use an adapter to Dual-link, it must be an Dual-Link DVI adapter (which also must be ab ACTIVE adapter).

If you use a cable for a Dual-Link display, it must be a Dual-Link DVI cable.

If you tried another DVI display and it does not work either, that suggests the DVI port on the card may be blown.

You can't support more than two "legacy" (non-DisplayPort family) displays at once unless some are using ACTIVE adapters.

The Sapphire HD Vapor-X has two DVI ports, see - http://www.sapphiretech.com/productdetial.asp?Pid=9213647F-B1DB-4945-BE33-8E1353 666B91&tag=download&lang=eng

One of these is listed as a DVI-A which means analogue and would only be suitable for analogue displays in other words VGA displays despite the fact it is a DVI connector. See http://www.networktechinc.com/blog/differences-between-dvi-connectors-and-signal s-2/276/ for an explanation of the different types of DVI connector.

The other DVI connector is a DVI-D connector which is a digital connector i.e. a 'real' DVI connection. 🙂 This is the one you need to use for the Cinema Display. You have not specifically stated which Cinema Display you have, as indicated by Grant larger Cinema displays need a 'dual-link' DVI-D interface and cable. Again if you refer to the NetworkTechInc article you will see that for Dual-Link support you need more pins, according to the picture on the SapphireTech webpage this card should have a dual-link interface although it does not specifically state this in the text. Based on my genuine Mac Edition 7950 card I would expect the Vapor-X to also be a dual-link capable connection.

You can confirm which Cinema Display you have by checking this article - Apple - Support - Technical Specifications

I would think the following would likely apply -

• The Vapor-X video card has a dual-link capable DVI-D interface
• The Cinema Display has a built-in cable
• If the Cinema Display built-in cable is a DVI cable it will - duh! have enough pins and that should be all you need
• If the built-in cable is not a DVI cable e.g. it is an old style ACD connector then you need two things, an Apple ACD to DVI adapter and a dual-link DVI cable (male to male), this is the ACD adapter https://www.amazon.com/Apple-M8661LL-DVI-Display-Adapter/dp/B00011KHT2 which is long discontinued
• If the built-in cable is a Mini Displayport cable it cannot be connected to the Vapor-X card
• If the built-in cable is a Thunderbolt cable it cannot be connected to the Vapor-X card

Cinema Display wider than 1920 wide (such as 30-in) requires Dual-Link DVD. All adapters and cables must be Dual-Link capable to pull this off, and vendors are very sloppy about labelling them.

In general, if you are using adapters, you must complete all conversion in ONE adapter, "stacking" adapters is almost never going to work.

But you’re saying that I can’t just plug the display into the DVI port on the card?

Of course you can plug the display directly into the port on the card, if the display has a captive cable (some do, some do not). If and only if you are using a third-party cable, you must assure yourself that your cable is indeed a Dual-Link DVI cable (they all look alike from the outside). And it you already have two other legacy cards powered up, some need ACTIVE adapters on those others, or test not more than two displays at once.

When I asked, you provided very little information about exactly what you were using and how you are connecting these. There are many different cinema displays, with many different cable arrangements and adapter setups that seem like they should work (but do not in certain edge cases). Many users have trouble with the complex interfacing to these cinema displays -- there are a lot of pitfalls.

Without enough information, I am forced to do a mind-dump of all possible related issues that I can think of, so that you can consider (and hopefully reject the ones that don't apply to your situation).

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If anything, Readers complain that I am too BLUNT when making suggestions. I am not implying anything, except that maybe that card is Broke, and IF you have not fallen into some of the obvious traps I already mentioned, you would need some more known-good things to test it with.

I get the impression you have previously used the same Cinema Display on the Mac via an older video card meaning you have proven the display is working. Please confirm.

I also get the impression you have previously used the same Vapor-X card in a PC successfully meaning it also has been working.

Is it possible to try the Vapor-X card in the PC with the Cinema Display connected to it?

What MacOS are you working in?

Which cinema display, with which interface?