imac keeps flashing black screen

[madeirabhoy]

apologies i posted this in iMac forum and got no answers, but maybe its not specifically an iMac problem, I've no idea if its hardware or software related.


just in the last week or so my mac has started, maybe only once or twice a day, flashing to a black screen just for half a second. always when I'm doing something, never when its idle. the easiest way i can explain it is either its a bit like when you watch someone logging into your mac using screen sharing (I'm not suggesting its this) or your screen saver goes to kick in.

now its an iMac 2011 so I'm scared its the graphics card going, but i don't think so. it could be something software related, i recently downgraded to yosemite from el capital beta. maybe i should try upgrading to the gold master.

ill twice a day, sometimes playing start craft 2, sometimes in safari, the screen will go black, its not a flash but its not long, half a second.

 

[madeirabhoy]

right i don't think its hardware, because its doing it tons now but when i restart in windows 10 it doesn't do it

 

[madeirabhoy]

this is really doing my nut in. doing it more than ever. in os x at least once every 5 mins, screen goes black for half a second. I've installed the El capitan GM in case it was something in yosemite. I've stopped every startup thingy like dropbox etc, so there's nothing else running. even if I'm just in safari it does it every 5 mins. in fact its mainly in safari but then I'm mainly in safari.

going to play some windows games for a bit to see if it does it but on previous tries it hasn't.

 

[sraosha]

this is really doing my nut in. doing it more than ever. in os x at least once every 5 mins, screen goes black for half a second. I've installed the El capitan GM in case it was something in yosemite. I've stopped every startup thingy like dropbox etc, so there's nothing else running. even if I'm just in safari it does it every 5 mins. in fact its mainly in safari but then I'm mainly in safari.

going to play some windows games for a bit to see if it does it but on previous tries it hasn't.

Same thing here on a late 2009 iMac with SSD and ATI Radeon HD 4850 512 MB. Flickering on loooong startup and then certain apps, like skype is flickering like a badly adjusted 1980s TV set. Very weird and of course everything was so much better and working fine with Yosemite.

To me it seems that something with the graphics card and El Cap is not working together well.