Archived - Resetting PMU on Power Mac G5, Power Mac G4, Power Macintosh G3
Learn about the Power Management Unit (PMU) on Power Macintosh G3, Power Mac G4 and Power Mac G5 computers, and how to reset it.
The PMU on the Power Macintosh G3 computers, Power Mac G4 (PCI) and Power Mac G4 Cube is known as the "Cuda button". In the later models It is identical in function and appearance to the PMU.
Resetting the Cuda or PMU also resets date and time settings. After the reset, on some Power Macs, the system clock is set to 00:00, 01 Jan 1904 for computers with Mac OS 9 or 00:00 (GMT), 01 Jan 1970 for computers with Mac OS X.
Important: The Cuda for the Power Macintosh G3 All-In-One, Power Macintosh G3 Desktop and Power Mac G4 Cube is not easily accessible. You may wish to take these models to an Apple Authorized Service Provider to reset the Cuda.
The PMU is a microcontroller chip that controls power functions for the computer. The PMU is a computer within a computer, as it has its own memory, software, firmware, input/output, a CPU, and more. Its function is to:
- 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.
Over time, the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, or not seeing devices plugged into the USB and FireWire ports, among others.
Resetting the PMU is not intended for resolution of a stall or situation in which the computer is unresponsive. A PMU reset should not be necessary except as a last resort in cases where a hardware failure of the power management system is suspected. Performing a PMU reset returns the computer hardware, including NVRAM, to default settings and forces the computer to shut down.
For most situations, a restart is sufficient. If the computer has stopped responding, try these steps, in order, until the computer responds:
- Force Quit (Option-Command-Escape)
- Restart (Control-Command-Power)
- Force Shut Down (press the power button for 10 seconds)
Important: Only perform a PMU reset on the computer if none of the above steps resolved the situation. If this is the case, see below for instructions on locating the reset button or key combination for your model of Power Macintosh G3, Power Mac G4, or Power Mac G5.
Resetting the PMU or Cuda:
- If the computer is on, turn it off.
- Disconnect ALL cables from the computer, including peripherals and power.
- If possible, move the computer to a place where you are not standing on carpet.
- Open the case and ground yourself by touching part of the metal frame inside the computer.
- Find the Cuda or PMU button
- Press the Cuda or PMU button ONCE. Do not press the button more than once before starting the computer up again.
- Wait 10 seconds, then reconnect the cables you removed in step 2 and turn the computer on.
- If the computer still does not respond after resetting the PMU, the computer may require service from an Apple Authorized Service Provider.
How to find the Cuda
The Cuda for the Power Macintosh G3 All-In-One, Power Macintosh G3 Desktop and Power Mac G4 Cube is not easily accessible. You may wish to take these models to an Apple Authorized Service Provider to reset the Cuda.
For Power Mac G5
Power Mac G5 (Early 2005):
Power Mac G5:
For Power Mac G4
Power Mac G4 (Digital Audio edition):
Power Mac G4 (Gigabit ethernet edition):
Power Mac G4 Cube:
Power Mac G4 (AGP edition):
Power Mac G4 (PCI edition):
For Power Macintosh G3
Power Macintosh G3 (Blue & White edition):