G4 Power Mac Sleeping/Shutdown Problem

Background

So I inherited a G4 Power Mac (Gigabit Ethernet Macintosh) a couple of years back from my brother which we used as our main family desktop for a while. It had a graphics card crashing problem that after US$50 at the local Mac store was diagnosed as a processor daughter card problem. Ebay and US$200 later and I had a new card and a great desktop. It is [still] a great computer and extremely usable under the latest 10.4.9 Mac OSX even though we have replaced it with a dual G5 that I got off Ebay.

The problem is that whenever we go to sleep the computer, it immediately powers off. I've been fighting with this problem for a while and I think it was one of the reasons why we went for the G5 upgrade. I don't have a solution to this problem right now but I wanted to document my progress in the hope that this will help someone else or maybe someone else has a solution.

In looking through the various boards via Google, there are ton's of people with sleep, shutdown, power-off, wakeup, etc. problems. Most of them have to do with Mac Powerbooks and the like which is understandable but some also have problems with desktops.

What I've Done

Here are the things that I have done which have not fixed the system:

Loaded the system from scratch multiple times. Fresh 10.4 install and fresh 10.4.9 combo upgrade package.
Tested the motherboard battery. Good 3.6+v.
Reset the PMU by pressing the motherboard button.
Took all of the cables off the motherboard and replugged them back in.
Disconnected all of peripherals except for the primary hard disk.
Pulled out the only card aside from the Apple graphics card.

Each of these steps in combination or by themselves did not fix the problem.

Interesting Links

How to reset the Power Management Unit which controls the sleep/power subsystem.
Interesting page about using ATX power supplies with your Macintosh. This is complicated because the Gigabit Ethernet models need a +28v line which is not provided by ATX power supplies.
Another page on ATX power supplies and Macs. Good diagrams and instructions.

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