Ticket Options

Question Profile

Question Details

TICKET ARCHIVE -> iMac screen dimming

selwest - Apr 16, 2007 - 6:22 am

My father has an iMac with a flat panel. After he has been using it for roughly half an hour, the screen starts to fade to white. Everything on the screen fades to white -- the window contents, the menus, the desktop. Everything.

I was playing around with this when I was visiting, and discovered a few really odd things.

1. The screen saver did not suffer from this. When I put it in screen saver mode, the colors were vivid and the blacks were really black.

2. If I used Safari to navigate to a web page that was very dark (such as the current Apple home page, with the picture of iPhone on a black background) the entire screen went back to normal: vivid colors, black blacks.

3. If I created a new tab in Safari, and navigated to a page that was very white (such as apple.com/support) the entire screen faded to white again, even the menus. I could toggle between the two tabs (apple.com and apple.com/support) and move the entire screen from fine to white.

4. If I made the Safari window smaller, the effect of toggling between the two windows affected the desktop that I could see in the space surrounding the Safari window. On the home page, all the icons and the desktop picture were vivid. On the support page, all the icons and the desktop picture were so washed out as to be virtually invisible.

5. If the computer is left in this condition for an hour or so, it will return to normal. Another half an hour of working with it, and the white screen comes back.

6. We raised the computer onto a cookie rack, to see if cooling the CPU would help. This made no difference.

Any ideas?

ishan - Apr 17, 2007 - 8:45 pm

It could be a video card going bad. There are some freeware utilities to test your video card available on macupdate.com and versiontracker.com, but they mainly test performance. If you have the original CDs that came with your father's iMac, there's an application on them called "Apple Hardware Diagnostic Utility" or "Apple Hardware Utility." Following the instructions in the Read Me file, boot up with that CD and let the program check all your components, including your video card. Other commercial programs, including Tech Tool Pro can do the same thing. If that says everything's OK, reset your PRAM by holding down command/option/p/r keys simultaneously while booting up until you hear three successive startup chimes, then let go. If that doesn't work, boot up in "Open Firmware" (hold down comamnd/option/o/f simultaneously at startup). At the prompt, type reset nv-ram, followed by a carriage return, then type reset-all, followed by a carriage return. Then type reboot and the iMac will boot nomrally.

Also check your vido card using System Profiler (in your Applications folder). Does it find the video card and say anything about problems with it?

If none of this works, follow the instructions on Apple's support pages to reset the SMC for your particular iMac (there are different instructions for different models). Finally, if that doesn't work, have it evaluated with an overnight stay at an Apple Store or authorized retailer so that they can reproduce the problem. Your video RAM or some other part of the video card may be going bad (which is what I suspect) and if the iMac is under warranty, the motherboard, to which the video card is welded will be replaced free of charge. If it not under AppleCare, you have a very expensive repair on your hands. I hope not.

Hope that helps and please let us know what happens. Thanks.

selwest - Apr 18, 2007 - 8:58 pm

Thanks for the thorough answer and all the suggestions. I have begun taking all the steps you recommended. I'll update this when I have either solved the problem or hit a dead end.