I have a few friends with such and the replacement motherboard to cure such failures is more than what I see refurbs going for. Example? http://www.geeks.com/products_sc.asp?cat=608 (avoid those C grades) and under 399 for something newer and made by apple.
Bob
I am trying to run Apple Hardware Test on my iBook G4, but it keeps freezing during the logic board test for both the extended and quick tests. I do not have any of the original discs that came with the machine, so I found a dmg online for the aht and burned it. The filename was 018-2056-A.dmg.
Now, my original problem was that my ethernet was not working. I was getting a self-assigned IP address (you know, the kind that don't work), which I considered par for the course for the network here until I realized that this was the case even when there was no cable plugged in. I also noticed that the device on the other end of the cable does not recognize that its connected to anything at all when I plug it into my Mac. Suspecting that my nic might be DOA, I tried running Apple Hardware Test, but of course, that's freezing whenever I run it. I find this odd, because I'm not having any other issues with the machine, and I don't understand why a bad nic would prevent the test from completing. Regardless, I'm used to troubleshooting PC's, so I thought I'd come here for some help. Thanks in advance for your assistance.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic