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I have an interesting, yet very frustrating problem. I have two computers, both running win7 32 bit, and both with ATI Firepro V4800 graphics cards. Both are using the DVI port and two DP to DVI adapters to connect 3 monitors.

One of them is able to display three desktops, while the other fails at enabling the third, displaying "cannot save changes" in display properties while requiring that one monitor must be disabled when making the change in CCC.

I've verified that both computers have the same driver version and that both are using the same DP-DVI adapters.

This articles suggests a few things to try, but none of its suggestions seem to work either.

I'm kind of at my wits end, hence my posting here. If this is not an appropriate question for SU, I apologize.

I admit that I am not very familiar with the differences between dual link and single link DVI, and that is something I have not verified is standardized between the two computers. Is that a possible reason one is working and the other isn't? How do I check if the DVI cable is a single link, or dual link?

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What happens if you switch the 3rd monitor (and cable and DP->DVI convertor) between the computers? Should that work then what happens with only part of the set swapped? –  Hennes Sep 12 '12 at 15:43
    
@Hennes I made the swap, and on the one computer is still running the three displays, but the other computer still is not. –  Jared275 Sep 12 '12 at 15:56
    
Assuming you rebooted in between you know can ignore three potential problem areas. It is a start. - You could try 0) make a backup) 1) deinstall driver software 2) reboot, clean leftovers from drivers. 3) reboot. 4) reinstall drivers. 5) reboot. 6) test again. –  Hennes Sep 12 '12 at 16:01
    
@Hennes: Before I do that, what exactly do you mean by "clean leftovers from drivers"? –  Jared275 Sep 12 '12 at 16:12
    
Check for left over folders, possibly containing configuration files. Optionally run a registry cleaner or a generic cleaner (I do not work for Piriform but I am quite fond of ccleaner). –  Hennes Sep 12 '12 at 16:20
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3 Answers

I had been using two passive DisplayPort-to-DVI adapters and one plain DVI cable fine when I was running three monitors; two were the same size, and one was a larger size. I was able to fix this problem by switching one of the adapters to be an active DisplayPort-to-DVI adapater.

Now the V4800 runs three monitors with different resolutions successfully (1680x1050, 1920x1200, and 1280x1024).

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up vote 1 down vote accepted

Uninstalling, and completely removing all of the driver files with the Driver Fusion utility recommended here, and then reinstalling driver 8.773.1.1000 seemed to do the trick.

I suspect that installing the newest driver would have worked as well, but I knew that the older driver worked on the other computer, and I didn't want to risk having to do the process again.

Thanks to Hennes for recommending this approach, and allquixotic for the info on DVI,

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Are all three monitors exactly the same on both computers? If not, you may be hitting a resolution limit.

The V4800 is an Evergreen-era GPU (actually one iteration later) so I'm a little surprised that it doesn't support up to three 1920x1080 displays...

I admit that I am not very familiar with the differences between dual link and single link DVI, and that is something I have not verified is standardized between the two computers. Is that a possible reason one is working and the other isn't? How do I check if the DVI cable is a single link, or dual link?

Single link DVI has "missing square pins" or "missing holes" (depending on whether you're looking at male or female connector).

Dual link DVI has square pins all the way across.

The difference:

various DVI connectors pinouts

Single Link has a lower maximum resolution (or lower refresh rate if higher resolution) because it can transmit less data with less pins. Dual Link can transmit the highest maximum resolution / refresh rate. Cable lengths also can affect resolution.

For a full description, see Wikipedia.

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The two computers do have different monitors. The one that is working has two 1680x1050's and one 1920x1080. The one that isn't working has three 1920x1080's. I lowered the resolution two 1680x1050 for the monitors, but that didn't make a difference either. –  Jared275 Sep 12 '12 at 15:58
    
Also, I just confirmed that both computers are using all single link DVI-D cables –  Jared275 Sep 12 '12 at 16:09
    
@Jared275 try those three 1080p monitors on the working PC and let us know if it fails or not. –  gronostaj Feb 28 '13 at 20:41
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