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Display in Safe Mode vs. Normal Mode

Late 2006 iMac recently started to have constant freeze up issues and horizontal lines in display. From what I have read, the likely culprit might be a video card. But I noticed, when the iMac starts up in Safe Mode, the machine operates fine and with no random horizontal lines in display. My question, what system items related to display/video are not loaded in safe mode that is making this difference ?

iMac, Mac OS X (10.4.11)

Posted on May 7, 2013 5:30 PM

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16 replies

May 8, 2013 6:35 AM in response to den.thed

Thanks for the link to Safe Mode info. And I realize Safe Mode loads certain extensions, but it was my observation during safe boot that my display did not have horizontal lines. My objective is to start machine in normal mode, disable problematic display/video extensions, and hopefully machine operates fine along with the proper display. I am trying to identify the display/video items/extensions to disable and should of worded my question differently.

May 8, 2013 7:04 AM in response to JeffreySmith

It's most likely not displaying those artifacts in Safe Mode because Quartz Extreme graphics is disasbled, only a bare bones graphics configuration. Probably not extensions related. More likely the GPU or GPU chip has failed. It might be the graphics drivers. For that you could reinstall, but it's usually not that.


Safe Mode in Mac OS X v10.5 or later also disables Quartz Extreme (hardware accelerated graphics).

You could try running the hardware test in extended, but getting a negative may not be all that meaningul, since it's not a great diagnostic. Might need to run several loops.


http://support.apple.com/kb/ht1509

May 8, 2013 8:16 AM in response to JeffreySmith

According to that KB article, whether or not you have it, it won't be disabled in Safe Mode, so it's not that. Have you installed any non-Apple programs that would have placed extensions or made system modifications?


Open Terminal in Utilities and copy/paste


kextstat | grep -v apple



Are you running any A-V? And yes run the AHT again in extended mode.

May 8, 2013 8:54 AM in response to JeffreySmith

In that case, I think my original diagnosis is the most likely and that KB article is incorrect. Not for your OS, but here's someone who claims to have disabled it. You could do a search for "disable quartz extreme OSX"


If you can do that, I don't know what effect that will have on graphics rendering where it will be needed. Sounds like you'll be running crippled. I'd make a backup before trying this. That's really all I know.


https://discussions.apple.com/thread/3993919?start=0&tstart=0

May 8, 2013 6:26 PM in response to JeffreySmith

Those models had issues with lines on the display that required replacing the Display. There was even an extended warranty program that ran for a year or so after the Apple and Apple Care warranties ran out.


From this point on it will only get worse and you will either start getting more line or the lines will turn into wider bands.


You have several options.


1. Replace the display. (which will cost more than the iMac is worth if you can find a replacement)


2. Connect an external DVI or VGA monitor to it and disconnect the internal monitor.


3. Buy a new iMac and sell that one on e-bay or craigs list for parts.

May 9, 2013 3:51 AM in response to JeffreySmith

Jeffrey, some years ago I was able to get Apple to extend the time on one of the repair programs by saying that I shouldn't be penalized just because my computer happened to last longer. The store denied my request, but I contacted Apple executive customer care, who authorized it. A major obstacle might be that they don't have those screens any longer.

May 9, 2013 5:04 AM in response to JeffreySmith

there were a couple of recent threads in similar vein - removing the graphics driver kext(s) seemingly allowed a regular boot at the expense of slow/no graphics & 'dvd player app' not working. Needed to know what graphics chip the imac used, then the relevant files were removed. Far from ideal, and you should follow the good advice given already before pursuing that.

May 9, 2013 7:35 AM in response to JeffreySmith

If you really want to get into this, you don't necessarily have to remove the extensions. You can use sudo kextunload, which will disable them without deleting them. To reverse you would use sudo kextload. That way you can test a particular kext for its effect.


Open Terminal in Utilities and leave a space after sudo kextunload then drag in the kext in question. Hit return, whereupon you will be asked to enter your admin password, which you won't see anywhere when you enter it, and given a scary warning about using sudo. Hit return again. Getting a new $ sign prompt will mean it's been unloaded. You may also get a message saying it's not allowed or has failed, for one reason or another.


Not sure if a restart will be required or not after the unloads.


I wouldn't do this however without a reliable backup, since you might inadvertently remove disable a kext that will prevent booting.

Display in Safe Mode vs. Normal Mode

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