For the past few months my late 2013 iMac 21" has intermittently shown a screen display that has distorted colours somewhat similar to the colourful patterns you get in oily water. The seriousness and frequency occurrence of the distortion varies such that I've struggled to get a screenshot,
Last night I did manage and it seemed to be happening as I logged on - maybe 50% of the time. Sometimes it would improve after a short while, other times the display would stay distorted. My housemate has a different user profile and has also experienced the problem, so I know it is not an issue specific to my profile.
I contacted Apple Support on Twitter last night and they had me confirming iOS version (latest 10.12.1), presence of other peripherals (none other than an external HDD that has been plugged in since iMac purchase). Next step when I get home this evening will be to set up a test profile.
A week or so back I came home to find the screen was black with just a few notification panels superimposed in the top right corner. It took several reboots before I got my screen display back. That time, Apple had me perform a nvram reset and it hasn't recurred yet but the screen display issue isn't fixed.
My concern is that I'm heading for a hardware failure and my AppleCare expires before Christmas so am keen to get a resolution. Any ideas about what it could be and what Apple might have me do next? I have tried Googling the issue but nothing similar seemed to show up.
Last night I did manage and it seemed to be happening as I logged on - maybe 50% of the time. Sometimes it would improve after a short while, other times the display would stay distorted. My housemate has a different user profile and has also experienced the problem, so I know it is not an issue specific to my profile.
I contacted Apple Support on Twitter last night and they had me confirming iOS version (latest 10.12.1), presence of other peripherals (none other than an external HDD that has been plugged in since iMac purchase). Next step when I get home this evening will be to set up a test profile.
A week or so back I came home to find the screen was black with just a few notification panels superimposed in the top right corner. It took several reboots before I got my screen display back. That time, Apple had me perform a nvram reset and it hasn't recurred yet but the screen display issue isn't fixed.
My concern is that I'm heading for a hardware failure and my AppleCare expires before Christmas so am keen to get a resolution. Any ideas about what it could be and what Apple might have me do next? I have tried Googling the issue but nothing similar seemed to show up.