For the second time in six weeks, Apple yesterday delivered a firmware fix designed to stop 27-inch iMac screens from flickering.
Initial reports from users who installed the update were mixed, with more saying that the flickering continued than saying Apple 's second try had resolved their iMac's flaky display.
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"The 27-inch iMac Display Firmware Update 1.0 updates the display firmware on 27-inch iMac computers to address issues that may cause intermittent display flickering," Apple said in a curt description of Monday's fix .
In late December, Apple released a 27-inch iMac graphics firmware upgrade that was also pitched as a fix for flickering. Most users that reported the results of that update, however, said that it had not solved their problems .
Somewhat the same reaction was evident late Monday, although only a handful of users had posted their findings on the enormous support thread dedicated to flickering screens. "The second firmware didn't help me either," reported "dxgriffiths" on the 1,600-message thread. "Still getting little dropouts and surges in brightness every few minutes."
"I just installed the update, as it was restarting I had 2x blackscreens happen, which had not happen[ed] on this machine only the occasional flicker," added "Leisas4" on the same thread an hour later. "Not a good sign."
Others, however, said that the update had done the job. "Firmware seems good to me," said "Bamtan" just after midnight on Tuesday.
Display issues have plagued Apple's 27-inch iMac desktop computers since the new machines debuted Oct. 20 . Users have reported cracked screens, a yellow tint to the display, black banding and, of course, the irritating flickers.
The problems prompted Canadian Web developer Scott Pronych to collate the complaints on a specially built site, and reportedly was the reason Apple slapped a two-week shipping delay on 27-inch iMacs in mid-December 2009. Eleven days ago, Apple increased the delay between ordering and shipping a 27-inch iMac to three weeks, again raising rumors that the California computer maker was withholding new machines as it tried to figure out the cause of the various display problems.
Those rumors gained momentum Monday when the English-language version of the MacBidouille site cited a source who claimed that Apple had shut down the production lines for the 27-inch iMac, and would not turn the lines back on until it "found a reliable and definitive fix" for the display issues.
Pronych, who has heard from Apple resellers in the past about the 27-inch iMac's troubles, today said he couldn't confirm that Apple had, in fact, halted production. But there was certainly evidence that customers' orders were being delayed. "I've been fielding lots of e-mails today from irate people who are having their orders pushed back," Pronych said in an e-mail late Monday.
But delays aren't universal. "Apple is still shipping some computers, as a couple people wrote me today that they are expecting deliver of their iMacs this week, at least based on the courier tracking," said Pronych. "[But] it remains to be seen when these computers were manufactured."
Pronych based his last comment on data he pulled from his Apple iMac (Fall 2009) Issues site, which contains more than 1,600 individual reports of problems, 44 percent of them related to screen flickering.
Of the 198 iMacs that users reported receiving in January, 91, or 46 percent of the total, were actually assembled in 2009. The largest one-week batch represented -- Apple marks its machines by the week of the year they came off the line -- was the first week of 2010. Only 7 of the 198 iMacs shipped, or less than 4 percent, were manufactured after the second week of this year.
"It appears that not everything is fresh off the assembly line," Pronych observed. "For example, the iMac I received this month was a  Week 51 model." That iMac was Pronych's third; he returned the first two because of display problems.
The 294KB firmware update can be downloaded from Apple's support site .
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld . Follow Gregg on Twitter at @gkeizer , send e-mail to email@example.com or subscribe to Gregg's RSS feed .
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This story, "Apple issues second firmware fix for iMac screen flickering" was originally published by Computerworld.