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Backlight dies, it's not the inverter or LCD

I'm troubleshooting a 12" iBook 1.33 Ghz. Boots up normally but LCD backlight dies after boot process ends. It also goes to hibernate repeatedly after a few seconds but can be awakened by pressing the space bar. I've replaced both the inverter and LCD panel but no joy. If I hold <option> key after the welcome chime sounds, the screen goes to display the hdd icon as the only bootable OS X, and the backlight does not go out, even after waiting 30 minutes if I just let it be. The arrow cursor works before the hdd icon comes up but it's very sluggish and moves very slowly. After the hdd icon comes up, the cursor moves normally.

Is it possibly the software or bad hdd, or bad logicboard?

Update

It's a 12 inch iBook, Model A1133, 1.33 GHz. I can't verify the serial number by software because the screen darkens before I can call it up, and there's no info in the battery compartment like the powerbooks.

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look on the sidewalls in the battery compartment

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Bernie, looks like software based on "and the backlight does not go out, even after waiting 30 minutes if I just let it be. " Hardware would not care and would continue to turn off. Just to make sure, what exact model iBook do you have, if you can give us your computers serial number we can properly identify your hardware.

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Did you try to boot from another OS, from the installation disk or from an external hard disk ? If you then get a constant backlight you know that the issue is software related and you'll need to reinstall the OS on the internal drive.

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That's my next step. But the original installation disk has been long gone, and I'm trying to dig up an external disk with bootable OS X.

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Hmmm, an idea just popped up in my head. If I connect my working powerbook in target mode and connect it to this iBook via firewire, and then power the ibook and press <option>, maybe the OS in my powerbook can be used as the startup disk!

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yes good idea !! Try it and keep us informed.

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Well, I did boot up my powerbook in target mode, connected it by firewire cable to the iBook, power up the iBook and immediately pressed <option> key. Shortly, the ibook screen showed the 2 bootable OS'es. I chose the powerbook hard drive, but there's no change. The iBook screen still goes dark and the machine goes into hibernation. Looks like it's really a logicboard problem.

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Bernie crwdns2934231:0crwdne2934231:0
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