User Guide

iMac (24-inch Early 2008) Troubleshooting — General Information 200
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-specication or no SDRAM or the RAM installed does not •
meet the appropriate specications, 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 veried to work
correctly on another system (i.e., “known-good”) or order new memory.
Firmware Updates
Firmware is the name given to software that is written into memory circuits such as ash
memory, that will hold the software code indenitely, even when power is removed from the
hardware. Firmware on Intel Mac computers is designed to be updated if necessary through a
software update.
Information about rmware versions for Intel Macs can be found in Knowledge Base article
303880 Mac OS X: Firmware Updates for Intel-based Macs.