The conversation on this page has been archived and is no longer active.

G4 AGP Failed powering up.

Message #1 - Posted 2004/10/11 - Kenny

Hi I have g4 agp and having power failed during startup.
The symptom is when I power up, fan is start running with single beep and front light is on but power goes off within a seconds. G4 even don't spit out diagonsys message beep because power goes off too quickly.

Could anyone have suggestion what could be a problem ?

Thanks in advanced.

Message #2 - Posted 2004/10/12 - Duff

First think I would do is reset the PMU.
Have you tried this?

Previously, Kenny wrote:

Hi I have g4 agp and having power failed during startup. The symptom is when I power up, fan is start running with single beep and front light is on but power goes off within a seconds. G4 even don't spit out diagonsys message beep because power goes off too quickly.

Could anyone have suggestion what could be a problem ?

Thanks in advanced.

Message #3 - Posted 2004/10/13 - Kenny

I just tried to reset PMU by pressing little button
near battery and does not solve the problem.
It looks like when I power on, fan start running and
power goes off like when car runs out of gasolin.

Message #4 - Posted 2004/10/13 - Duff

Did you remove the power cord and check the battery before resetting the PMU? If so, and you reset it correctly, the problem could be one of the items listed below in diagnostics.

Resetting the PMU on the Logic Board

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, Troubleshooting General/ Logic Board Troubleshooting - 11 I/O, two crystals, and a CPU. Its function is to:
Ä Tell the computer to turn on, turn off, sleep, wake, idle, etc. Ä Manage system resets from various commands.
Ä Maintain parameter RAM (PRAM).
Ä Manage the real-time clock.
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 crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. The PMU chip is located on the underside of the logic board at U20; refer to the Power Mac G4 (AGP Graphics/ Gigabit Ethernet/Digital Audio) Logic Board Diagrams for the location of the PMU button.
Many system problems can be resolved by resetting the PMU chip. Whenever you have a unit that fails to power up, follow this Troubleshooting General/ Logic Board Troubleshooting - 12 procedure before replacing any modules:

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 crash the PMU chip.
3. WAIT ten seconds before connecting the power cord and powering the computer on. If the computer powers on, go to the next step. If the computer does not power on, there is something else wrong with the computer; refer to the symptom/cure chart, ≥Startup≤ in this chapter.
4. Run Apple Hardware Test and return the computer to the customer.

From G4 AGP Diagnostics:

System shuts down almost immediately after startup

1 Power Macintosh G4 (PCI Graphics): Reset the Cuda chip. See ≥ Resetting the Cuda Chip≤ in this chapter.

2 Reset the logic board:
Ä Power Mac G4 (AGP Graphics): Refer to ≥Resetting the PMU on the Logic Board≤ in this chapter.

Ä Power Macintosh G4 (PCI Graphics): Refer to ≥Resetting the PCI Logic Board≤ in this chapter.

3 Check the modem connector (J27). If the connector has any bent pins, replace the logic board.

4 Replace the processor module.

5 Replace the power supply.

6 Replace the logic board.

Previously, Kenny wrote:

I just tried to reset PMU by pressing little button near battery and does not solve the problem.
It looks like when I power on, fan start running and
power goes off like when car runs out of gasolin.

Need Help? Have a Question?

Looking for more help, comments, and answers?

Ask your questions on Ask Different. Ask Different is a community of Apple users ready to help.