nMP - HDMI video issues?

I know there probably aren't a lot of you out there yet with a similar configuration to mine .... But just wanted to pass along my experiences and see if anyone else has run into them too.

I have the new Mac Pro configured with 3 27" LG monitors (IPS panels running at 1920x1200 native resolution). The first one is attached directly to the HDMI output on the nMP, while the second is attached via a Mini-DisplayPort to HDMI dongle. As per Apple's documentation, I purchased the Apple Mini-DisplayPort to dual-link DVI adapter ($99 -- grr!) to make the 3rd. display work properly. (Apparently the nMP can't drive more than 2 displays off of Mini-DP dongles and/or the HDMI port on the back of the machine. If you want to add a 3rd., 4th., etc. and they're not true Apple branded Thunderbolt displays, you need the expensive dual-link DVI adapter for each of them.)

So anyway.... that was all fine and well, except after I bought a new triple display stand for my monitors and took all of them off of their factory stands -- my 6 foot HDMI cable barely reached even the display closest to my nMP. So I went out and bought a brand new 12' HDMI cable (a "Craig" branded cable sold at the local CVS pharmacy -- which I know may not be the fanciest brand, but it felt thick and well made enough).

Well.... now, it seems whichever monitor I attach that 12' cable to? That monitor has a problem where it powers itself completely off when the nMP puts the displays to sleep. The other 2 screens come right back to life with a click of the mouse and/or tap of the keyboard.

I find it hard to believe that the extra 6' of cable length actually makes the signal so weak it starts having these problems, but perhaps so?!

Answering my own question ....

Well, I got another HDMI cable to test with, and it appears things are working fine now with the 12' cable replaced with a 10' cable I borrowed from my Roku box upstairs.

So I know my issue was the new 12' HDMI cable I was using, but not sure if it exceeds some kind of maximum usable length for the nMP -- or if it's simply a cable with some odd wiring?

Ah, good to know!

I guess Apple's knowledge base note on nMP video configurations never mentions that, because they don't sell their own active single link DVI to Mini-DP adapter?

I wasn't aware such a thing existed or I would have gone that route.

demars said:

Just for the record, if your resolution does not actually require dual link DVI (maximum resolution for single link is 1900x1200) you can get a much cheaper single link DVI to DisplayPort active adapter (they run around $30). What won't work (for more than two ports) is a passive adapter.

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That makes sense.... But just curious? Would these cheap, longer than 3 metre cables still work properly in most television applications then? Or are you saying they're simply junk and really don't work well in ANY application?

(I'm just thinking these cables would get returned so often, they'd take them off the market, if there weren't people successfully using them with other things. Are computer to video display applications more demanding than most audio-video uses for them?)

theSeb said:

It's the cable. Once you go beyond around 3 metres many of the cheap cables don't work properly. It has nothing to do with the mac.

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