iMac (27-inch, Mid 2010) — General Troubleshooting 22
2010-09-09
Resetting the System Management Controller (SMC)The System Management Controller (SMC) is a chip on logic board that controls all power
functions. If computer is experiencing any power issue, such as not starting up, not displaying
video, sleep issues, battery management, or fan noise issues, resetting SMC may resolve it. To
reset SMC on an iMac:
1. Shut down the computer.
2. Unplug all cables from computer, including power cord.
3. Press and hold the power button for 5 seconds.
4. Release the power button.
5. Attach the computer’s power cable.
Note: If you press the power button while inserting the power cord, the iMac will enter
a mode in which the fans run at full speed. For more information, refer to kbase article
TS1433: iMac: Fans run at full speed after computer turns on
6. Press the power button to turn on the computer.
For more information, refer to:
kBase #HT3964: Intel-based iMac: How to reset the System Management Controller
Resetting Parameter RAM (PRAM)PRAM stores certain system and device settings in a location that Mac OS X can access quickly.
Exactly which settings are stored in the computer’s PRAM varies depending on the type of
computer as well as the types of devices and drives connected. To reset PRAM:
1. Shut down the computer.
2. Locate the following keys on keyboard: Command, Option, P, and R. You will need to hold
these keys down simultaneously in Step 4.
Note: If the keyboard does not have an Option key, use the Alt key instead.
3. Press power button.
4. Immediately press and hold Command-Option-P-R keys.
Important: You must press this key combination before the gray screen appears.
5. Hold down keys until the computer restarts, and you hear the startup chime a second time.
6. Release keys.
For more information, refer to:
kBase #HT1242: Mac OS X: What’s stored in PRAM
kBase #HT1379: Resetting your Mac’s PRAM and NVRAM