On the late 2005 PowerMac G5, the PMU has been replaced by a newer, but equivalent, microsystem, referred to by Apple as the SMU (the System Management Unit). So, what could it be? I recalled that the PowerMac G5, like many of its predecessors, has a power management unit (PMU) on the motherboard, sporting the famous CUDA (Capacitive Unit Discharge ASIC) switch, which allows an externally initiated reset of the PMU. For whatever reason, just like the last time, it took TWO restart attempts to get the machine to “catch” and boot, but just like last time, on the second attempt it roared back to life and has been stable ever since. In fact, I got the machine “back on the air” today after just such a sequence of events. The behavior was too unrelated to anything else I could determine, and did seem at least temporarily correctable by simply unplugging the machine, leaving it to sit and then trying again. With that safely out of the way, something told me the issue had to be power related. Eventually, the fans would ramp up to full speed and stay that way.Īll along, I had been assuming that the issue lay with the RAM upgrade I was attempting, but as chronicled in my last post, this was definitely not the case.

The fans would come on, the disks would spin, but nothing else would happen. The symptoms the machine was exhibiting will be familiar to regular readers of this blog: no start up chime and no signs of intelligent life after powering on the machine. My last two posts have dealt with my attempts to recover bootability (if that is a word!) to my late 2005 Power Mac G5, 2.3 GHz dual core (not dual CPU). Good luck! This post explains the details behind this prescription. The first restart attempt may fail, but the second should work. Unplug your machine, leave it sit overnight and try again the next day.

Synopsis: no start up chime from your PowerMac G5? Suspect the SMU.

Dual cpu in a power mac g5 case