There is a power-on self test that resides in the ROM of the eMac. This test automatically runs whenever the eMac 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 eMac 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 slots accept standard PC-100 or PC-133, 168-pin DIMMs).
Three Beeps: No RAM banks passed memory testing.
Four or Five Beeps: Bad checksum for the remainder of the boot ROM. The ROM is bad.
Important: Apple highly recommends removing the battery when handling the logic board. Make sure to use proper ESD protection when handling modules.
The battery on the logic board controls the stored system settings, such as date and time. It is only necessary to test the battery when you can't power on the computer, or the date and time are reset every time the AC power is removed.
The battery is also used to power the PMU chip (because the PMU chip keeps time and must always be running) when the computer is unplugged from the wall (AC power). The PMU is very sensitive and touching any circuitry that is connected to the PMU can cause it to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Once the battery goes dead, the PMU will reset the time and date every time the AC power is removed. To fix this situation, replace the battery and reset the PMU (refer to "Resetting the PMU on the Logic Board" mentioned earlier in this chapter).
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