Apple iMac G5, 20-inch - Manual (Page 258)

34 - iMac G5, 20-inch Troubleshooting Symptom Charts
Yes: The hard drive needs to be replaced.
No: Go to the next step.
13. When pressing the internal power button to power on the computer, does LED #2
come on momentarily, or not at all?
Momentarily: The logic board has detected 12v, but the power supply cannot
maintain it. Your power supply needs to be replaced.
Not at all: Your logic board needs to be replaced.
14. If the computer will ONLY start up from the internal power but will not power on from
the power button on the back cover, the back cover may need to be replaced. Unplug
the computer and remove the back cover. WIth the back cover removed, plug the
power cord back in. Touch and hold an insulated screwdriver to the two contact points
shown below:
Does your computer start up when holding your screwdriver to these two contact
points?
Yes: This shows that the power button switch is working correctly. The back cover
should be replaced.
No: This indicates that the power button switch is not working correctly. The logic
board should be replaced.