Chosen Solution
Dear iMac lovers, my 2nd hand imac keeps reboot to a un-usable degree since the start of June. i had bought it in June 2021 from an Indian couple. During Feb-Apr, i turned on Quick Time, screenrecording for -100 hours over 12 weeks. the machine alum case was hot. suspecting, the last straw on a camel. i connect my imac to external screen. surprsingly, the imac runs smoothly.
my question is: is 4-hour QuickTime and hot alum case causing death on this old imac (27’, 2011 mid, AMD radeon HD 6970m)?i bought a SSD to replace HDD, auto reboot still happens. My next target is: PSU? or GPU? (i will not buy any new/used logic board from any party because too too expensive. US $200-700. )how to distinguish failure due to PSU or due to GPU? the Samsung external display via mini display port cable runs smoothly. i guess PSU is at fault. because LED monitor consumes 40-50watt. my samsung external mon is powered itself, without relying power from imac PSU. is my line of thought logical, accurate and relevant? Update (06/25/2022)
Gfxcardstatus not running my desktop imac … The Diagnostic by apple only indicated absence of thermal sensor in SSD card at HDD bay. The GPU AMD Radeon HD looks working…its temperature is 33 Celsius degree, more than CPU at 29 Celsius degree. How to explain zero score in nova benchmark? Thanks for Dan’s insight . Update (06/25/2022) Hi Lemerise
I had suspected the PSU too. Before delivering to technician for repair, i did check the parts on psu. It looked normal on appearance . But i have no relevant tool or schematic to check GPU performance , i eventually stopped my urge to buy new PSU. And just let a professional technician to discover what is happening . I did buy a new wired keyboard when my imac started frequent breakdown. Before, i used a Bluetooth keyboard ,which is out of battery very soon in a few weeks time. Maybe this wired keyboard is my last straw on a heavy camel. It puts extra, though however minute, irreversible an old powerhouse… Will keep you, Dan and oldturkey3 posted of latest observations and discovery of my old machine repair status…
I would reconnect the internal display and then run the onboard diagnostics to see what it tells you. Restart your system and press the D key to enter Reference: Mac startup key combinations I’m suspecting your discreet GPU has failed. Diagnostics runs on the firmware driver for the Intel Intergraded graphics engine it has. Your external display is able to run using the same Integrated graphics engine, but this time using the OS driver, as it we default to that. You can also prove this using this great app gfxCardStatus
Remove the unit power supply and check for faulty capacitors. It would not be surprising that a 11 years old PS needs a recapping. I just worked on this iMac model and even if the power supply was working there was 3 damaged capacitors. Top of the cap is doomed, its a sign the cap is failing soon or later.
