Late 2012 27" Imac brightness fluctuating instantly.

richard371

macrumors 68020
Original poster
Feb 1, 2008
2,338
579
A few days ago I would be sitting in front of the iMac and the brightness would fluctuate instantly 5 or 10 times in about 15 seconds from the 80% I have it set on to about half that and back and forth then stop. It would be fine for awhile then do it again. This happened pre mavericks. I have updates to mavericks, reset the PRAM-SMC etc. I have the autobrighness turned off.

Today it has not happened but after turning the computer on after about 15 mins the brightness instantly drops about 20% or so. I checked the brightness keys F1/F2 and nothing has changed.

The problem is that it is very intermittent and I doubt the Apple store will believe me. I tried recording it on my iPhone but every time I get to the cam app it stops. My wnty runs out late November.

Anyone exp this?
 

jordanm86

macrumors regular
Oct 21, 2011
223
34
I had a similar issue on an iPad (3rd Gen) - screen brightness would either occasionally flicker or would be completely random on waking (autobrightness off and no change to the actual brightness level setting).

Eventually one side of the screen went dim, took it to an Apple Store, they restored it and it was fine for another few weeks. Happened again, they wiped it again and was ok for another week. Happened a third time and they replaced the unit - one of the backlight elements was faulty.

Not necessarily relevant but thought I'd end the story: the replacement unit was fault and would ask for a passcode even without one being set after a full DFU reset... had that unit replaced and been all good since :D

With your iMac, is the entire screen brightness uniform or is it brighter on one side to another? Could be a dodgy connection or mainboard failure?
 

richard371

macrumors 68020
Original poster
Feb 1, 2008
2,338
579
Thanks. It's perfectly uniform.

I had a similar issue on an iPad (3rd Gen) - screen brightness would either occasionally flicker or would be completely random on waking (autobrightness off and no change to the actual brightness level setting).

Eventually one side of the screen went dim, took it to an Apple Store, they restored it and it was fine for another few weeks. Happened again, they wiped it again and was ok for another week. Happened a third time and they replaced the unit - one of the backlight elements was faulty.

Not necessarily relevant but thought I'd end the story: the replacement unit was fault and would ask for a passcode even without one being set after a full DFU reset... had that unit replaced and been all good since :D

With your iMac, is the entire screen brightness uniform or is it brighter on one side to another? Could be a dodgy connection or mainboard failure?
 

Hexley

macrumors 6502a
Jun 10, 2009
822
21
A few days ago I would be sitting in front of the iMac and the brightness would fluctuate instantly 5 or 10 times in about 15 seconds from the 80% I have it set on to about half that and back and forth then stop. It would be fine for awhile then do it again. This happened pre mavericks. I have updates to mavericks, reset the PRAM-SMC etc. I have the autobrighness turned off.

Today it has not happened but after turning the computer on after about 15 mins the brightness instantly drops about 20% or so. I checked the brightness keys F1/F2 and nothing has changed.

The problem is that it is very intermittent and I doubt the Apple store will believe me. I tried recording it on my iPhone but every time I get to the cam app it stops. My wnty runs out late November.

Anyone exp this?
Were you able to resolve the brightness issue of your 2012 27-inch iMac?