Last night my PowerBook suffered the same Power Management Unit-related failure that I’ve described before, and so today I booked a session at the “Genius Bar” in the Bellevue Apple store. Inevitably, the “Genius” was unable to reproduce the problem: we restarted and power-cycled the machine several times, but it always restarted successfully. We agreed that it was probably something to do with the power load: I normally have my PowerBook plugged in to a FireWire hard disk, another USB disk (for Time Machine), an external display, a couple of camera docks, and an iPhone dock. I use a powered USB hub, but even so I’m sure that the load affects the PowerBook’s power subsystem. “Oh well: at least it’s working,” said the genius, as he sent me on my way.
I got home, and fired up the machine. Everything looked OK… except that I couldn’t connect to the Internet. According to Network Preferences, I was connected to my AirPort Express hub, but I had a self-assigned IP address. I re-entered the WEP password ((Yes, I know WEP is broken, but I have a couple of legacy devices that don’t do WPA.)), but I still couldn’t get out. Re-acquire DHCP… nothing. Reboot PowerBook… nothing. Power-cycle AirPort Express… nothing. Run AirPort Assistant… it couldn’t see the AirPort Express. Finally (guess what) I reset the PMU on my PowerBook, re-entered the WEP address (and the date, etcetera), and mirabile dictu I was back in business.
My diagnosis: the PMU is dying, slowly, and inducing a variety of failure modes. The trick is going to be inducing a hard failure,, or at least a failure that the Genius will take seriously. Time to start systematically unplugging stuff and testing for failure, I think…