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iMac (24-inch Mid 2007) Take Apart — General Information 207
Power On Self Test (POST)
Intel-based Mac computers such as the iMac (24-inch 2007) rely on a combination of tones and
blinking LEDs to display Power On Self Test (POST) error codes.
If the computer detects out-of-specication or no SDRAM or the RAM installed does not •
meet the appropriate specications, the screen will remain black but the computer will beep.
This error condition may be due to physically damaged RAM, installing the 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 the tones until the computer is turned o.
The solution to both of these situations is to rst re-seat the memory and test the computer •
again. If the memory fails the POST test again, try memory that has been veried to work
correctly on another system (i.e., “known-good”) or order new memory.
How to Reset the System Management Controller (SMC)
The System Management Controller (SMC) is a chip on the logic board that controls all power
functions for your computer. If your computer is experiencing any power issue, resetting the SMC
may resolve it. The SMC controls several functions, including:
Telling the computer when to turn on, turn o, sleep, wake, idle, and so forth.•
Handling system resets from various commands.•
Controlling the fans.•
Note that resetting the SMC does not reset the PRAM. Resetting the SMC will not resolve issues
in which your computer is unresponsive—in these situations, restarting your computer will
generally suce. If your computer isn’t responding, perform these steps one at a time, in this
order, until the issue has been resolved:
Force Quit (Option-Command-Escape).1.
Restart (Control-Command-Power).2.
Force Shut Down (press the power button for 10 seconds).3.
Resetting the SMC can resolve some computer issues such as not starting up, not displaying
video, sleep issues, fan noise issues, and so forth. If your computer still exhibits these types of
issues after you’ve restarted the computer, try resetting the SMC.
To reset the SMC on an iMac (24-inch 2007)
From the Apple menu, choose Shut Down (or if the computer is not responding, hold the 1.
power button for approximately ten seconds until it powers o).
Unplug all cables from the computer, including the power cord.2.
Wait at least 15 seconds. The SMC reset occurs automatically once the iMac has been 3.
unplugged from the AC power source for several seconds.
Plug the power cord back in, making sure the power button is not being pressed at the time. 4.