The computer automatically performs a power-on self test when it is turned on after being fully shut down (not a restart). This section describes what to do if beeps are heard during the startup. When this occurs, the sleep LED will stay on—occasionally flashes.
MacBook Pro relies on a combination of tones and blinking sleep LED to display Power On Self Test (POST) error codes.
If the computer detects no SDRAM (Synchronous Dynamic Random Access Memory, also referred to as RAM) or the RAM installed does not meet the appropriate specifications, the screen will remain black but the power LED on the front of the computer will blink once per second to signal the error. 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 blink the power LED on the front of the computer three times, pause, and repeat the blinking until the computer is turned off.
Was this article helpful?