View Full Version : Experts Help! PowerMac G4 - Power up - light comes on - no power

Jan 7, 2010, 06:18 PM
Hi, I have an old G4 PowerMac and suddenly today when I went to start it, I pressed the power up button, the light comes on, but then it goes off when I take my finger off and there is no power, no fan, no nothing...

I have done some reading and learned it could possibly be the PMU (Power Manager Unit) on the motherboard?

I came across this article which gives the steps in Resetting the PMU on the Logic Board but I am nervous about tinkering around as I am not experienced at all with this kind of stuff.


Any insight as to what the problem could be, or if an expert could confirm if it is the PMU and what steps, if any, I can take to try to resolve it?

Thanks a lot

Jan 7, 2010, 06:32 PM
If you follow the instructions, it won't hurt the machine to reset the PMU. Also check the battery (though I've booted Sawtooths without batteries even in them before). Try reseating the RAM as well, and try taking out a few sticks and seeing if that makes a difference.

Jan 7, 2010, 08:05 PM
Thanks, seems to be working after the reset.