Apple 2009 iMac - Page 19

iMac (21.5-inch, Late 2009) — General Troubleshooting 19
2010-11-18
Common Reset Procedures
Power On Self Test (POST)
Intel-based Mac computers such as the iMac rely on a combination of tones to indicate Power
On Self Test (POST) error codes.
• If the computer detects out-of-specication or no SDRAM, the screen will remain black
but the computer will beep. This error condition may be due to physically damaged RAM,
installing incorrect type of RAM, or not having RAM installed.
• Some RAM may appear to pass the Power-On-Self-Test (POST) but still cannot be used by
the operating system. In this case, the computer will display a gray screen, sound three
tones and repeat tones until computer is turned o.
• The solution to both of these situations is to rst re-seat memory and test computer again.
If memory fails POST again, remove all installed memory and test by installing one by one
each memory module that has been veried to work correctly on another system (i.e.,
“known-good”) or order new memory.
• A sequence of tones heard at startup or a no video symptom may also be xed by
temporarily removing/replacing the backup battery.
For more information, refer to:
kBase #HT2538: iMac (Mid 2007) and later models: About new startup tones
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, or fan noise issues, resetting SMC may resolve it. To reset SMC on an iMac:
1. From Apple menu, choose Shut Down (or if the computer is not responding, hold power
button for approximately ten seconds until it powers o).
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, making sure power button is not being pressed.
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 #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 iMacs: Resetting the System Management Controller (SMC)