iMac (27-inch, Mid 2010) Symptom Charts — Startup and Power 39
2010-09-09
Intermittent Shutdown

Troubleshooting Shutdown Causes

Always run the latest available Apple service utilities to check for any abnormal value reading
from a thermal, a voltage, or a current sensor, or from a fan speed meter. The log les may also
report the cause of a previous shut down(s).
Collect all available info from user on shut down occurrence details: periodicity, power state
when issue happens, running applications, running time before shutdown.

Shutdown events can be categorized into four dierent areas.

1) User-related shut downs:

A computer shut-down event may be caused by user operation. The following shut down
methods should not be considered as a failure, unless the power button is found to be
defective.
• Selecting Shut Down by choosing the Apple () menu from the upper-left menu bar and
then choosing Shut Down.
• Pressing and holding the power button for 10 seconds
• Programming a timed shutdown in the Energy Saver preferences: refer to  menu>System
Preferences>Energy Saver
Suggested troubleshooting steps are:
• Reset the SMC: Refer to: kBase #HT3964: Intel-based iMac: How to reset the System
Management Controller
• Check Energy Saver preferences settings: choosing the Apple () menu>System
Preferences>Energy Saver
• Test the Power On button for an intermittent short that would force computer to shutdown.

2) Activity-related system shut downs:

• System could not succeed the standard shutdown process and had to force shutdown
• An installed watchdog detected that an application did not respond within specied time
(this watchdog can be enabled on Mac O X Server Energy Saver preferences)
These shut downs may be linked to system settings, devices drivers, applications, or operating
system freezes.
Suggested troubleshooting steps are:
• Check the system logs and activity monitor utility for clues on the freezing process,
• Check for available software and rmware updates for installed device drivers, applications,
or operating system
• Start the system from a known-good / up-to-date bootable drive for issue reproduction.