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I recently got a Mac Mini at work. I have two of the same monitor connected to it:

  • one over HDMI->DVI adapter and DVI cable, and
  • one over MiniDisplayPort->VGA adapter and VGA cable

Sometimes (often several times a day, not predictable) the display that is connected over HDMI->DVI will show rainbow static (similar to the snow on a TV, except multicolored). If I disconnect the adapter from the Mac, the situation resolves itself temporarily. If I simply sit and wait, the problem stops after several seconds to a minute.

I have replaced the DVI cable. I have swapped the two monitors, and whichever is connected over HDMI->DVI will snow, and the other will not.

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Have you maybe tried with another monitor model/brand? If you say the two are alike, maybe it's a really weird hardware combination issue. I have a Mac Mini at work that also doesn't play that nicely with some monitors. Also, have you installed all software updates? –  slhck Jun 11 '11 at 21:13
    
I installed all software updates. I tried it with a different monitor, DVI cable and HDMI adapter (all my own personal hardware) and my monitor did not seem to have the issue. I am presently using the old monitor, the replaced DVI cable, and my own HDMI->DVI adapter, and have not seen the issue all day. I am going to exchange the DVI->HDMI adapter and hope that this fixes my issue. –  jaf1230 Jun 13 '11 at 20:08
    
Came into work just now and got snow. I have changed everything past the Mini (adapter, dvi cable, screen). It could (I guess) be the model of the monitor and/or the resolution, but my guess is that it's the Mini. –  jaf1230 Jun 15 '11 at 13:10
    
Hm, could definitely be a hardware issue on the Mini. Like the Thunderbolt ports of the new Macbooks -- they had some issues like you describe too. If you can't try with another Mini it'd be best to get a replacement. –  slhck Jun 15 '11 at 13:12

2 Answers 2

Often this is caused by a Sync issue. I've found that when I am called in for this issue that most often it is solved with a higher quality cable. I would recommend a 24 or 28 gauge HDMI to DVI cable, and skip the adaptor all together.

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I have a Hot Corner that puts my MBP to sleep, which I use when getting up at work. When I come back and wake the computer, yeah, about half the time I see (taste?) the rainbow on my external Samsung monitor (connected with Thunderbolt to DVI). Using the Hot Corner again and then waking the computer again always fixes it.

I think David Joyce is onto something: it sure looks to me like the monitor is just not waking up quite as quickly as the Mac expects it to, and they get out of sync. Then, once the monitor is woken up, sleeping the Mac and waking it again fixes the problem.

Since this is Apple, I think it's likely that Macs are just not very tolerant of non-Apple peripherals with complicated protocols, like displays and WiFi, so I'd suggest getting a Cinema Display. Whether this is because non-Apple peripherals are crappy, or because Apple doesn't bother testing much with non-Apple stuff...the world may never know.

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