Troubleshooting Power-On Self Test - 11
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.
One Beep:
No RAM is installed or detected.
Two Beeps:
Incompatible memory is installed. (The iMac
ships with PC-100 SDRAM and does not accept SDRAM SO-
DIMMs or EDO memory).
Three Beeps:
No RAM banks passed memory testing.
Four or Five Beeps:
Bad checksum for the remainder of the
boot ROM. The ROM (which is located on the processor module)
is bad.