[Andrej]

iMac G5 1.6 GHz
Mac OS X 10.5.3

External Hard Drive: OWC Netune 160 GB, works fine
Firewire 400


I saw in Activity Monitor that my Finder was taking up 50-60% of my CPU, and that my external (Time Machine hard drive) was in use and that some process was causing my Finder to be so CPU intensive and to use my external hard drive to do so. Hence, I hit the Eject icon in one of my Finder windows to disconnect the hard drive via software, and sure enough, the Finder CPU slowed way down back to normal, and my external hard drive spun down.

So, I went to power off my external hard drive and turn it back on (the usual off/on reset), but as soon as I did that, my iMac G5 turned itself completely off.

And I cannot get it to turn back on!

I'm way too panicky to spend 60 minutes searching all corners of the internet to know what's going on.

What other info do you all need in order to help me out?


What Ive tried to get the iMac to start back up:
[1] Pushed the power button: nothing.
[2] Pushed the power button for 6 seconds, plugged and then unplugged the power cable, as well as the external hard drive, on and off, nothing.


Now what do I do??


[3] When I connect the power cord at the AC wall outlet end of the power cord into the AC wall outlet, there is a spark, and so I know that power is going into the computer end of the cable.

[Cold Warrior]

unplug all peripherals and reset the SMC

iMac G5: How to Reset the SMU

Originally Posted by KB HT1767

Summary
This article applies to the iMac G5, the iMac G5 (Ambient Light Sensor), and the iMac G5 (iSight).

The SMU (System Management Unit) is a microcontroller chip on the logic board that controls all power functions for your computer. If your computer is experiencing any power issue, resetting the SMU may resolve it. The SMU controls several functions, including:

Telling the computer when to turn on, turn off, sleep, wake, idle, and so on.
Handling system resets from various commands.
Controlling the fans.
Products Affected
iMac G5 (17-Inch iSight), iMac G5 (17-Inch), iMac G5 (20-Inch iSight), iMac G5 (20-Inch), iMac G5 ALS (20-Inch), iMac G5 ALS (17-Inch)
Note that resetting the SMU does not reset the PRAM. Resetting the SMU will not resolve issues in which your computer is unresponsive—in these situations, restarting your computer will generally suffice. If your computer isn't responding, perform these steps one at a time, in this order, until the issue has been resolved:

Force Quit (Option-Command-Escape).
Restart (Control-Command-Power).
Force Shut Down (press the power button for 10 seconds).
Resetting the SMU can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and so on. If your computer still exhibits these types of issues even after you've restarted the computer, try resetting the SMU. To reset the SMU on one of these iMacs:

Turn off the computer by choosing Shut Down from the Apple menu, or by holding the power button until the computer turns off.
Unplug all cables from the computer, including the power cord.
Wait 10 seconds.
Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
Let go of the power button.
Press the power button once more to start up your iMac.
The original iMac G5 model has a small button on the main logic board that will also reset the SMU, allowing you to reset the SMU easily if you have the back cover removed. The original iMac G5 will start up when pressing this button.

[Andrej]

I waited 10 seconds, fudged the cable back in while holding onto the Power button, kept holding onto the button until I could finally get the cable all the way in with my other hand, let go of the power button, waited another 5 or so seconds, then pushed the power button again...

that did not work. The computer still did not turn on.


I think that somehow something got fried in turning off the external hard drive. But I am not sure.

[CharlesS]

See if your iMac falls under this:

Apple - Support - iMac G5 Repair Extension Program for Power Supply Issues

[Andrej]

No, this is a model 2004 iMac.

I have no idea if this means anything, but an hour or so before the iMac turned itself off, I was using my external hard drive as 1 partition for time machine and 1 partition for whatever else, and I used Leopard's Disk Utility to repartition everything to a single partition for Time Machine. That all went through fine. Could that have anything to do with the Finder going to 50-60% CPU like 35 minutes later? All I was doing was browsing web pages and playing iTunes radio. No Spotlight activity, no nothing. Should I open up my computer to see if something got blown up? Should I wait overnight to see if it'll just turn itself back on? This computer does not work under the above link's repair program, and it has already had a logic board replacement 1-2 years ago, and the logic board has been fine ever since.

[Andrej]

Nevermind, I followed: iMac G5: Troubleshooting when your computer won't turn on

I had to do a manual SMU reset.


Weird.

Now I want answers: Why the hell did turning on/off my external hard drive do this???

[Cold Warrior]

I've had to do the manual reset once before also, but on a first-gen flat panel iMac G4.

Glad you got it working.

[imitchellg5]

Originally Posted by Andrej 

Nevermind, I followed: iMac G5: Troubleshooting when your computer won't turn on

I had to do a manual SMU reset.


Weird.

Now I want answers: Why the hell did turning on/off my external hard drive do this???

My guess is that your iMac was supplying power to the external hard drive and for some reason freaked out. My iMac's done something very similar to that as well (1.8 GHz).

[chipchen]

Here's my two cents...

Sometimes weird things happen. And no one knows why. That's what I've had to learn to live with as an electronics troubleshooter.

[Andrej]

Alright, guys, I just came back from a 2-week vacation with my iMac unplugged (in case of power surges from wind storms, etc.). I go to plug my computer back in, and then I go to turn it on, and, as usual, it does not turn on. Gee, great, I have to go back to the back of the computer and open up the cover and do the manual reset again, I think.

THIS PROBLEM IS RESOLVED. The problem that a mechanical wedge-shaped button below the AC power cable female leads on the computer itself had to be pushed inward a few times. Edit: Actually, the computer seems to be showing its age. The power supply connectors are becoming loose...