When Apple first announced the 27-inch iMac last month, tech enthusiasts the world over were rubbing their hands together at the prospect of owning one of largest all-in-one computer screens ever built.

But many of those same buyers are now flocking to the Apple user forum to report a multitude of hardware problems and voice their disappointment with the new iMac.

More than 600 posts have been devoted to problems with the 27-inch machine on the Apple forum, with the most commonly reported fault manifesting as a flicker or blackout that happens intermittently when the screen is switched on. This issue has been reported by users as far afield as North America, Europe and Australia.

The new iMacs ... customers complaining about flickering screens and blackouts.

"Got my new iMac shipped from Shanghai the very day they launched. Was really excited but now really dissapointed by this recurring problem . . . Sometimes the screen completely blacks out for 2-3 seconds on intervals of 5-6 secs and the machine becomes useless," wrote a forum user in the US.

"My problem is that the display seems to have this glitch. It happens mostly when I switch on after the display has been asleep for a while. Apple do not know what the problem is as I am on to them almost every day," wrote an Australian user.

A number of YouTube videos have also been posted by users highlighting the problem, while some prospective iMac customers have decided to postpone their purchases until they are certain any reported problems are fixed.

"Thanks. Just canceled my iMac order. I could have lived with a screen that is really a big mirror but if it also flickers that is a showstopper, sorry Apple," said a forum user in the Netherlands.

The problems with Apple's latest batch of iMacs are not confined to flickering. Some US users have also complained about the high end units with Intel's Core i7 chip arriving dead on arrival (DOA) or with cracked screens.

Staff at the Engadget blog wrote: "We're a little more familiar with the DOA issue, since the new i7 we just bought doesn't boot at all".

Many users on the Apple forum have reported that the company is replacing their faulty units without cost, although one Australian user wrote on the MacTalk forum that he was being charged a US$70 shipping fee because he was not located near an Apple store.

"Apple have a fairly good DOA policy. If you get a Mac and it doesn't work right, you've got 14 days to contact Apple and tell them what's wrong and chances are they will give you a replacement Mac instantly," said Anthony Agius, editor of the MacTalk blog.

Apple would not comment on the nature or scope of the problems reported on its forum, but it advises any customer having an issue with a Mac to contact AppleCare for support on 133 622.

- Sydney Morning Herald