Apple IMAC User Manual - Page 94

Troubleshooting General/ Power-On Self Test - 1 2 Power-On Self Test There is a power-on self test that resides in the ROM of the iMac. This test automatically runs whenever the iMac is powered on after being fully shut down (the power-on self test does not run if the machine is only restarted). If a problem is detected during the test, you will not hear a normal startup chime. Instead, the system will beep as explained below. Refer to "Error Beeps" later in this chapter for instructions on how to troubleshoot and repair an iMac that sounds error beeps at startup time. Following is a definition of what the error beeps at startup time signify. • 1 Beep: No RAM is installed or detected. • 2 Beeps: EDO memory is installed. (The iMac ships with SDRAM SO-DIMMs and does not accept EDO memory). • 3 Beeps: No RAM banks passed memory testing. • 4 or 5 Beeps: Bad checksum for the remainder of the boot ROM. The ROM (which is located on the processor module) is bad.