iMac restarts when external monitor unplugged
This iMac will restart at the login screen or before it. First thing I tried was to reformat the hard drive and reinstall the OS with no luck. Basic SMC reset, etc.. have been completed as well.
Started with Apple Service Diagnostic (ASD) tests
Memory: Passed. Also took out each module individually and still restarted.
Hard Drive: Passed short test (long test was not completed). However, unlikely a hard drive issue. Computer will restart when booting off an external drive as well. Also pulled the HD while booting from external just to rule it out for sure.
CPU: passed tests
GPU: passed tests
Thermal sensors: Passed loop test (10 times).
Fan test: Fans passed tests (at all speeds)
*Does not boot in safe mode*
Opened the Mac up and cleaned a significant amount of dust out with air canister.
The iMac will stay on during testing without fans on full speed.
Checked the shutdown logs: kernel[0]: |Previous Shutdown Cause: -128
This is an unknown hardware error. Ram was checked and replaced with another set. Problem persisted.
UPDATE
The iMac will power on perfectly fine (without me having to make the fans spin full speed) as long as I have an external monitor attached. As soon as I unplug the monitor, the Mac will shutdown. This external monitor "fix" allowed me to check the temperatures with iStat and everything is perfect. It is definitely not thermal related. I am starting to suspect that maybe the integrated graphics have failed? Discrete graphics (Radeon) is being used while the external monitor is plugged in.
Is this a good question?
23 Comments
What does the onboard diagnostic LED's show? I'm thinking you have a power supply issue.
by Dan
I'll check that out as well. I have thought about the power supply as well... but it would be strange for the power supply to be the problem because the computer runs perfect as long as the fans are set to full speed.
Oh, also it runs without the fans running full speed while using ASD (apple service diagnostics). I would think if the power supply was the issue, it would also shut down during these tests)
by Campbell
onboard LED's are good by the way
by Campbell
I have done a little bit of research and I think I might have a way to solve the issue. I know that this computer has Intel HD 2000 graphics integrated. This is on the CPU in this machine. I have read that this integrated graphics is enabled (unlike what some people believe) and it is used for airplay purposes. It would make sense because that is some of the last things I see on some of the logs before a shutdown. I am going to try to find a way to completely remove airplay from OSX
by Campbell
You're confusing your self!
The integrated Intel graphics is used for a variety of uses as an example running diagnostics, safe mode and the OS installer. During the boot cycle for the second & third phase (when you see the Apple logo and when the progress bar goes across. Once you see the gray background change is when the GPU kicks in.
While I can't say for sure, I don't see why Apple would use the integrated graphics service over the dedicated for Airplay. I would expect the better would be used.
WTW: The Mid 2011 has a Intel HD Graphics 3000 not 2000. The 2010 iMac model's have the Intel HD Graphics 2000. Are we sure which model you have here?
by Dan
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