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TOPIC
- Tell the computer to turn on, turn off, sleep, wake, idle, etc.
- Manage system resets from various commands.
- Maintain parameter RAM (PRAM).
- Manage the real-time clock.
The PMU (Power Management Unit) is a microcontroller chip that controls all power functions for the computer. The PMU is a computer within a computer. It has memory, software, firmware, I/O, two crystals, and a CPU.
Its function is to:
DISCUSSION
- iMac (Slot Loading)
- iMac (Summer 2000)
- iMac (Early 2001)
This article covers repair procedures for authorized service providers on selected Apple products, but we have published them in the Knowledge Base for the general public for educational purposes. At this time, there are a limited number of repairs that a customer can perform and these are covered under the customer installable parts program http://www.info.apple.com/installparts . If you have not been authorized to perform these procedures, please contact Apple (800-APL-CARE in the USA) or your local authorized service provider to schedule a repair.
DANGER! This procedure exposes you to high voltages that can result in death or serious injury. DO NOT ATTEMPT THIS PROCEDURE IF YOU HAVE NOT BEEN CERTIFIED AS AN APPLE-AUTHORIZED TECHNICIAN.
Products affected
Solution
Whenever you have a unit that does not power up, resetting the PMU (Power Management Unit) on the logic board can resolve many system issues. Follow the steps below before replacing any modules.
Important : Be very careful when handling the main logic board. Remove the battery when handling the logic board so the PMU is not affected. The PMU is very sensitive and touching the circuitry on the logic board can cause the PMU to stop responding. If the PMU stops responding, the battery life is reduced from about five years to about two days if the PMU is not reset.
Refer to the logic board diagram below.
1. Disconnect the power cord and check the battery in the battery holder (BT1). The battery should read 3.3 to 3.7 volts. If the battery is bad, replace the battery, wait ten seconds, and then reset the PMU (refer to the next step). If the battery is good, go to the next step.
2. Press the PMU reset switch (S1) once on the logic board and then proceed to step 3. Do not press the PMU reset switch a second time because it could cause the PMU chip to stop responding.
3. Wait ten seconds before connecting the power cord and powering up the computer. If the computer powers on, go to the next step. If the computer does not power up, there is something else wrong with the computer. For more information on no power, refer to the article 95003: " iMac: No Power ".
4. Run MacTest Pro and return the computer to the customer.
Note : This entire procedure resets the computer's PRAM. Be sure to reset the computer's time, date and other system parameter settings before returning the computer to the customer.