Cooling problem after replacing video card
Yesterday I build in a refurbished Radeon 4850 512MB in my late 2009 iMac 27". It's an upgrade form the original 256MB which has broken.
The installation of the card went good so i took it for a test and everything seems to be running perfectly. After about 15 minutes of idle the mac goes in standby, when trying to wake up, the display stays black. A cold restart (holding powerbutton for 10 sec) the mac reboots (I can hear the chongsound) but even then display stays black. I tried serveral things but nothing really worked so I turned it off to try it in a couple of hours. I started the mac and voila, my display works again. My guess is that there is a cooling problem so I installed iStat to boost up the fans tot 1800. This worked cause the display didn't turn black.
Does anyone know what could be the problem why the mac doesn't managed the cooling it self?