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Aggie Mac Master
Aggie Mac Master, Mac Genius
Category: Mac
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Experience:  B.S. Biology from Texas A&M University and Long-time Mac User
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My new 24 iMac 2.8Ghz is set up, lovely, but acting

Resolved Question:

My new 24" iMac 2.8Ghz is set up, lovely, but acting odd. Whatever''s on the screen goes to gray or shades and repeats over and over making cursor insertion a challenge. Two or more documents reduce, split and rapidly oscillate. The harddrive icon won''t open when clicked. It chirps when I go into the dock, regardless of destination, and at other times on its own.

Spent time on the phone over the weekend w/ Apple Support and their solution is to send me FedEx labels for an exchange. Though just an end user, that seems unnecessary.

Ever come across this? Thanks in advance!


Submitted: 9 years ago.
Category: Mac
Expert:  Aggie Mac Master replied 9 years ago.
Step 1:
Get the program at You should use the native resolution for the 24" iMac (1920x1200).

Step 2:
In the program, go to the Custom tab. Press the + sign to create a custom setting. In the 'Timing Parameters' window, after making sure all the parameters are the same as the normal 1920x1200 setting, set the vertical scan rate at 70. Also, check the 'Positive synch' check-box. Save everything and reboot.

Step 3:
Open System Preferences, then Displays. Now you should have the Refresh Rate drop-down option enabled (should be 60). Select the 70 setting. Save and reboot.

Step 4:
You should have a flicker-free display now.

If this doesn't work, then go with the replacement option offered by AppleCare. I just bought a new 24" iMac too and I have not had any similar issue on it.

If there is anything else I can help with, please respond.

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