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Will not boot, but only fan starts up. Dead DC board?

This iBook has been working fine for years, and began to behave strangely quite suddenly: the screen flashed and audio played. At restart worked at first, then it crashed. We were able to run in FireWire mode to back up some files. A subsequent attempt to startup from DVD failed (and the disk will not eject).

Now it will not boot at all: no chime, no screen display, no FireWire disk mounting. A fan starts when power button is pushed, and stops when pwr btn is held down for a few seconds. Otherwise, nothing. Tried keystrokes for PMU reset, no help.

The battery is good (4 lights) and AC adapter seems ok. Could this be a DC board problem, or is logic board failure more likely? What to test first?

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I'm going to accept logic board failure as the answer to this, and many thanks to Dan for his response. I tore the iBook down, removed the hard drive and installed it in an older 12" 800MHz model. All the data is there. Along the way, I was also able to extract the DVD that had gotten stuck in the optical drive. So - I have parts! What fun.

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Jen please score and mark the question as answered, thx!

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Are you sure you reset the PMU correctly? It's not the first thing I would try. I would first reset NVRAM/PRAM Then I would try resetting the PMU Apple TN on Resetting the PMU.

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Thanks Dan. I followed your sequence (and realized I hadn't reset the NVRAM/PRAM correctly before). Now I can hear what sounds like the HD spinning up, but no chime, and the screen does not light up. That, and the fact that the fan comes on so quickly and loudly makes me think this is a logic board failure - maybe just the logic board battery as suggested in the Apple TN. Would you agree?

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Do you have a second mac and a firewire cable to connect the two together? Set your iBook into target mode and see if you can access it's HD via the other mac.

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Tried that earlier, to no avail. I'm in a different location now, and just discovered that the iMac I'm typing on has a completely different FireWire connector (grr!) for which I have no cable. So am putting the problem aside for today. Thanks, Dan.

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I agree that this is most likely logic board failure, but just one note -- G4s often get shorted out by loose screws on the underside of the board, and produce the "fan on high" issue you're experiencing. You might want to remove the lower shielding, and see if any screws underneath fall out, or if any of the screws connecting the board to the frame are visibly loose. Then, try powering on with the lower shielding removed.

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Jen Morris さん、ありがとうございました!
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