Currently Being ModeratedJul 29, 2012 3:13 PM (in response to Fused0ne)
I am having the same issue. iMac 29" Mid 2011, 16gb ram, upgraded to Mountain lion then my hdmi out to tv flickers and audio gets muted every few seconds.. very annoying. I am sure apple will be releasing a fix in the next update.
You can roll back by doing a clean install of lion provided you have time machine backups for the previous OS. If you bought your copy legitimately through the Apple Store, you can download the installation again from your purchases. Just use your time machine backup to restore your computer to the previous OS.
Hope this helps, and hope apple fixes this before you resort to downgrading.
Currently Being ModeratedJul 29, 2012 7:00 PM (in response to arnoldbn)
I hope they come out with a fix, unfortunatly I didn't have a drive to be able to use Time Machine so I could not make a backup.
I got both Lion and Mountain Lion from the App store, I bought my Mac last Sept after Lion had just been out for a bit so I was eligible for a upgrade... although the store said macs ready with Lion mine was not... but no biggie I updated it, thought I did find it odd that in Sept when I got it, it was still a Early 2011 model I would have figured it be late so no Power Nap for me... Anyways back on topic, I had a $100 credit to the app store I got for getting my mac at my schools Apple store so I thought eh, why not. I still had most of the credit so in a way Mountain Lion was free... I read as many reviews and opinions before doing so and I did not see anything regarding flicker issues until I saw it myself and searched specifically for that.
I do hope they update or something to fix this, its very frustrating. I can't imagine trying to back everything up manually elsewhere and do a clean install.
I tried to reset PRAM but it will not reset, cause I don't here the two start up tones your supposed to hear, I wonder if the settings or steps changed for Mountain Lion.
Currently Being ModeratedAug 1, 2012 7:40 AM (in response to Fused0ne)
I'm having the same issue with MacBook Pro + thunderbolt + Apple Cinema Display
Currently Being ModeratedAug 4, 2012 1:32 AM (in response to Fused0ne)
Same here on rMBP /w and external 27" acer monitor connected via HDMI.
Also sometimes when waking up from sleep the external screen display is comepltely garbled and i need to unplug to get it working again.
And the new AirSync Mirror is also playing up every time. At first activation it'll shrink the screen to 2/3rds of the tv screen. Need to Deactivate and reactivate for it to proper work.
So seems like there are screen issues all over the place.
Hoping apple will release a fix for that soon.
Currently Being ModeratedAug 4, 2012 3:25 AM (in response to Fused0ne)
HI Everyone, i have had the same issue i have an imac 27 inch and yesterday i upgraded to mountain lion, immediatly i noticed the screen flicker and came on here to see if there was a solution. i have however turned the brightness down slightly and it has cured my imac from flickering, maybe try this for now until apple sort it out. i have only done this aprox 30 mins ago and so far no problem, ill keep you posted if it starts again.
Currently Being ModeratedAug 4, 2012 1:23 PM (in response to Fused0ne)
Getting similar issue of infrequent screen flickering on 2011 MacMini running into a 2010 Cinema Display. Only happened since upgrade to Mountain Lion. Screen goes black for about half a second second and then returns.
Other than this, no issues at all and no error log entries of any relevance, or reports generated of incicdents at the time the screen flashes black.
Currently Being ModeratedAug 7, 2012 3:13 AM (in response to Fused0ne)
Similar things here. Bought an 27" Thunderbolt Cinema Display. When connected to my Retina MBP flickering at unpredictable moments. I don't know if it's a Mountain Lion issue, since I bought the display after the new OSX.
Currently Being ModeratedAug 7, 2012 5:27 PM (in response to Fused0ne)
Similar issue. As RMWoodward describes, my screen alternates from working for one second or so to all grey for a second or so to working for a second to all grey for a second.... constantly. My set up is a Mac Mini + HDMI cable + InFocus ScreenPlay projector.
I JUST bought the Mac Mini (shipped with Lion) and hooked things up. It worked fine. I then upgraded to Mountain Lion and suddenly the issue started. The HDMI cable should not be a problem as that gives no issues when I use it to connect my other computers to the same projector.
How do I go about downgrading to Lion again? I don't have any external drives.
Currently Being ModeratedAug 17, 2012 5:32 PM (in response to SombodyHelpMe)
Still no replies or news from Apple regarding, real shame.
Currently Being ModeratedSep 3, 2012 9:15 PM (in response to Fused0ne)
I wish I’d heard about this issue before updgrading to Mountain Lion a few hours ago. Now I have to determine the easiest way to downgrade back to Lion or just stop using an external monitor until a fix arrives. I'm using a 2011 11" MacBook Air, with a 24" 1920 × 1200 monitor connected to the Thunderbolt port with a Mini DisplayPort to DisplayPort cable.
Currently Being ModeratedSep 3, 2012 10:56 PM (in response to yonatron)
Now that'd be quite overkill to get rid of a single flickering to black and back to normal for connecting to a display. WHile surely it is annoying it does not repeat. Once you connected to a display and it flickered it won't bug you again until you disconnect and reconnect again.
Currently Being ModeratedSep 4, 2012 2:22 PM (in response to neongrau)
I’m not sure where you’re getting the idea that this is only happening once after connecting the display. Most people on this thread have said it happens repeatedly. With me there’s a brief flicker of a randomly-positioned horizontal band of pixels every few seconds, and several times a minute the screen goes completely black for up to 2 seconds. Either downgrading to Lion or temporarily forgoing the monitor are my only reasonable options, because this is more than slightly annoying.
Currently Being ModeratedSep 4, 2012 2:27 PM (in response to Fused0ne)
I had no luck with AppleCare phone support, but I have a Genius Bar appointment for Friday. I’ll report back here if they have anything useful to say.
So far, SMC reset, PRAM reset, reinstalling from the Restore partition, creating a new user account, and Safe Boot have all been fruitless.
The problem goes away when I boot from a Lion USB drive, so I know it's a Mountain Lion issue.
Currently Being ModeratedSep 19, 2012 6:53 PM (in response to Fused0ne)
Great news!! I just installed Mountain Lion 10.8.2 - and the flickering stopped. I'm guessing Apple has fixed this issue with their latest update. This issue appears to have been an issue with 10.8.1 only as 10.8.0 didn't seem to do this on my Thunderbolt display connected to my MacBook Pro [15-inch, early 2011].