iMac Manual
iMac (27-inch, Mid 2010) — General Troubleshooting 21
2010-09-09
Hardware vs. Software
For information on how to isolate a hardware issue from a software issue, refer to:
kBase #TS1388: Isolating issues in Mac OS X
For information on how to troubleshoot a software issue, refer to:
kBase #HT1199: Mac OS X: How to troubleshoot a software issue
kBase #TS1394: Mac OS X: Troubleshooting installation and software updates
kBase #HT2956: Troubleshooting Mac OS X installation from CD or DVD
Common Reset Procedures
Power On Self Test (POST)
Intel-based Mac computers such as the iMac 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, 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, poor connection, 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, remove all installed memory and
test by installing one by one each memory that has been veried 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.