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The pretty image above (image from apple discussions) just happened to my BTO Core Duo iMac 20", which was bought from a retailer. According to the link, this happens often when affected iMacs are woken from sleep. The effect completely fades away over 20-30 minutes. Apparently the motherboard or video card is overheating the display in sleep mode. Take a look at the discussion on Apple's website.

This is my second iMac. The first was received on 16th May (after ordering 4th May), and it was returned DOA on the 18th with a (different) video problem.

I received this Mac 15 days later on the 2nd of June. Note that this problem has only occurred once (so far) - this morning. Other than that, the Mac has been excellent (and I don't want to be without it now ;p). This iMac (bto 20", 256mb, 2gb, 500gb) is 9 days old - so if I am to return it within the 10 day 'early life' period, it has to be tomorrow.

I have two options.. I could return it and get a brand new machine, and risk dead pixels (or a generally worse machine) and up to 3 weeks wait; or I could just hold on to it and get it repaired at my leisure (a week max without it). What would you do - repair or replace?

I'd go for replace.

have you done the latest firmware, 1.0.1 and the smc update as well. id go for a replacement again - 3rd time lucky

<div class='quotetop'>QUOTE(The Architect.mac @ Jun 11 2006, 03:32 PM) [snapback]182491[/snapback]</div>Yep, while a firmware fix would be nice, everything is up to date. Although the problem seems somewhat common, at this stage there is apparently no official documentation on it. Seems like it has been going for a few months, with people just having their logic boards, displays, video cards, or whole computers replaced.

I'm just not sure if I want to erase, box up the whole thing, drive it back and wait a few weeks. It probably shouldn't take that long to do a BTO (according to Apple's website), but it seems to take 2-3 weeks from this retailer, who is just ordering through Apple like any other retailer would.

Is there any sense to replacing the whole machine rather than repairing it?

the same thing happened to mine after waking it from sleep after the first night (Friday morning) - vertical banding, black squares, severe interlacing (like a refresh rate issue), and discolored horizontal lines. You're right that most of it clears up, but some of it stuck around for a few hours, and one single-pixel line across the screen didn't clear up.

I took it back DOA, and got a new model that day. Since then, I've used it for a couple of days without updating the SMC firmware and by disabling the sleep option, and I haven't had any problems. These appear to be the two commalities with all the occurances of this issue (though waking from sleep looks like the trigger).

It does look like an overheating issue, though I'm not entirely sure how it's caused. In my case, it looks like it caused a more permanent display issue (the horizontal line) while all the other symptoms faded away. This was the techie's justification of the doa, as it was the only symptom that was still there (the techie did apparently know of the issue).

I'm following this issue with interest, as I want to use the sleep option - I've gotten so used to it having had the powerbook.

EDIT: Mine only had the extra RAM, so it wasn't BTO and I could take another model straight away - phew...

Update - I am getting a refund

I asked if I could hold on to the affected machine while waiting for a new one to be ordered. As expected, they said no, so I have arranged a refund instead.

I might wait for Rev B. Macrumors now lists the iMac as statistically "updates soon". Hopefully that'll be of the Core 2 Duo variety in 1-2 months ;p.

I've had the same problem with mine since waking it from sleep a couple times. I'm on applecare, so couldn't I technically wait till rev b and then claim that the problem just started, and replace it then?

<div class='quotetop'>QUOTE(Wrathchild @ Jun 13 2006, 05:23 PM) [snapback]183425[/snapback]</div>They will most likely replace the logic board, GPU, or display. That is what happened to everybody who had it 'repaired' in the Apple.com discussions page. Other people on that page either had their machine replaced (in its first 14 days), or simply turned off the display sleep function.

You could only really try for a Rev B iMac if you had your machine repaired at least 3 times.