Troubleshooting PowerBook G4 17" (#5): Charging problems, resetting the PMU
Troubleshooting PowerBook G4 17" (#5): Charging problems, resetting the PMU
A number of readers are reporting that the PowerBook G4 17" suddenly stops recognizing that it is plugged into an electrical outlet and switches to battery power.
Michelle Hoyle writes: "We have two of the first 17" PowerBooks to be available here in the United Kingdom. Both PowerBooks are intermittently experiencing a strange problem with the power adaptors. The machines will suddenly switch to battery power. A check of the power adaptor where it plugs into the computer will reveal no coloured power lights and the menu battery indicator will indicate that the PowerBook is indeed running from the battery. While this most often seems to happen at night, when we're not watching, it has also happened in the day while we're actively using the PowerBooks, without any noticeable power changes (dimming/brightening lights) or outages."
This problem can generally be rsolved by simply unplugging and re-plugging the power adapter. However, if you simply unplug the adapter at the computer end (the lighted tip end) and plug it back in, it does not solve the problem
Hoyle adds "To compound the strangeness, we actually have the two laptops plugged in differently. One is usually directly plugged into a UK wall outlet. The other one is plugged into a surge-protected power bar and the power bar is plugged into a large 1600-watt transformer box which outputs North American power."
One potential solution for this problem, based on previous cases that are similar, is to reset the Power Management Unit (PMU). The PMU controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and I/O including looking at the serial port and modem so it does not sleep when connected.
Apple says that over time, the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. Examples would be not turning on, not waking from sleep, not charging the battery, or not seeing the AC Adapter, among others.
The following is the procedure for resetting the PMU on the PowerBook G4 17":- If the computer is on, turn it off.
- Reset the power manager by simultaneously pressing and then releasing Shift-Control-Option-power on the keyboard. Do not press the fn (Function) key while using this combination of keystrokes.
- Wait 5 seconds.
- Press the power button to restart the computer.
If you are experiencing PowerBook charging problems, and have tried resetting the PMU, please let us know your results at late-breakers@macfixit.com.
Resources