If you ordered in an off brand of the charger, that may be what's failing. Also the outer ring of the jack sometimes get bent so that it doesn't fit snugly and causes sporadic contact. Look to see if it's a sloppy fit and squeeze it tighter if need be. Test the charger on another machine if you can. Only after you have determined the charger is good would I look at the DC IN port.
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Here's the DC-IN board: http://www.ifixit.com/iBook-Parts/iBook-G4-12-Inch-DC-In-Board/IF183-030
If you ordered in an off brand of the charger, that may be what's failing. Also the outer ring of the jack sometimes get bent so that it doesn't fit snugly and causes sporadic contact. Look to see if it's a sloppy fit and squeeze it tighter if need be. Test the charger on another machine if you can. Only after you have determined the charger is good would I look at the DC IN port.