HT202351: OS X: How to use multiple displays with your Mac in Mountain Lion and earlier

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jscmtl
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Q: IMac running 10.6.8, 2 Ghz Intel Core 2 duo, 3 gig 667 MHz SDRAM -using an external 21 inch Omnitech monitor for years, no problem- lately, my computer screens will temporarily go blue and the Hz rate changes from 59.9 to 60 image distorted. Help

IMac running 10.6.8, 2 Ghz Intel Core 2 duo, 3 gig 667 MHz SDRAM -using an external 21 inch Omnitech monitor for years, no problem- lately, my computer screens will temporarily go blue and the Hz rate changes from 59.9 to 60 image distorted on the external monitor. If I turn off and wait, it will go back to "normal" 59.9 Hz. Help!

iMac, Mac OS X (10.6.8)

Posted on Jul 3, 2015 9:58 AM

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jscmtl

Q: IMac running 10.6.8, 2 Ghz Intel Core 2 duo, 3 gig 667 MHz SDRAM -using an external 21 inch Omnitech monitor for years, no problem ... more

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  • by rkaufmann87,Helpful

    rkaufmann87 rkaufmann87 Jul 3, 2015 11:06 AM in response to jscmtl
    Level 9 (58,184 points)
    Photos for Mac
    Jul 3, 2015 11:06 AM in response to jscmtl

    The GPU may be failing. Run Apple's Hardware Test in extended mode 2-3 times back to back and if errors occur that confirms a hardware issue. Running AHT multiple times is necessary because it does not always pick up errors after the first or even second time. However when it does detect errors they are correct.

  • by jscmtl,

    jscmtl jscmtl Jul 3, 2015 1:35 PM in response to rkaufmann87
    Level 1 (0 points)
    Jul 3, 2015 1:35 PM in response to rkaufmann87

    Hi - sounds like a really good answer. The computer is getting a bit old. I will try this. Many thanks.