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Current version by: Dan ,

Title:

iMac restarts when external monitor unplugged (READ ALL)
iMac restarts when external monitor unplugged (READ ALL)

Text:

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.

Device:

iMac Intel 27" EMC 2429

Status:

open

Edit by: Campbell ,

Title:

iMac shutdownrestarts when external monitor unplugged (READ ALL)
iMac shutdownrestarts when external monitor unplugged (READ ALL)

Text:

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.
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.
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.

Device:

iMac Intel 27" EMC 2429

Status:

open

Edit by: Campbell ,

Title:

iMac restarts at login screen or before itshutdown when external monitor unplugged
iMac restarts at login screen or before itshutdown when external monitor unplugged

Text:

Okay, I have done a lot of testing and repairing in my life on Apple products. This one has me baffled. First of all, this iMacThis 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.
Okay, I have done a lot of testing and repairing in my life on Apple products. This one has me baffled. First of all, this iMacThis 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, which makes me think this can't be thermal related. However, in order to boot to an OS, the fans must be put to full-spin mode. For some reason, the Mac will stay on when booted to an OS when the fans are full-speed.speed.
The iMac will stay on during testing without fans on full speed, which makes me think this can't be thermal related. However, in order to boot to an OS, the fans must be put to full-spin mode. For some reason, the Mac will stay on when booted to an OS when the fans are full-speed.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.
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.

Device:

iMac Intel 27" EMC 2429

Status:

open

Original post by: Campbell ,

Title:

iMac restarts at login screen or before it

Text:

Okay, I have done a lot of testing and repairing in my life on Apple products. This one has me baffled. First of all, 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, which makes me think this can't be thermal related. However, in order to boot to an OS, the fans must be put to full-spin mode. For some reason, the Mac will stay on when booted to an OS when the fans are 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.

Device:

iMac Intel 27" EMC 2429

Status:

open