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-specification 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 off.

The solution to both of these situations is to first 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 verified 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 fixed by temporarily removing/replacing the backup battery.

2010-09-09

iMac (27-inch, Mid 2010) — General Troubleshooting 21

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Apple MD094LL/A manual Hardware vs. Software, Common Reset Procedures Power On Self Test Post