Fan powers on but nothing else, what could it be?

My ibook G4 will not turn on, the fan powers up and caps lock key light turns on.

I tried replacing the Hard drive, and it's still doing the same thing, how can I tell if it's the motherboard or the logic board?

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Thanks everyone I got it up and running with just a little pressure on the bottom case when it gets hot I loose it, so I'm going to try a shim since I don't have those soldering tools and have never soldered before.

Definetly the U28 chip problem though!

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The shim repair wont last long. I'd try to find a tech that would do the soldering job for me.

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If the ibook G4 only gives a black screen and fan running full speed when powered on the problem is often related to the U28 chip issue (desoldered pins) on the logic board. The chip has 28 pins and is located near the DC in power socket under the logic board. You need to solder back two small desoldered pins (#1 & #28) to their contact point on the logic board. You need to use a pencil thin soldering iron like the Weller WM120 to avoid bridging the other pins:

http://www.amazon.com/Weller-WM120-120v-...

U28 chip location:

http://www.flickr.com/photos/metasim/532...

http://www.macrevitalise.co.uk/overview%...

http://fernieville.files.wordpress.com/2...

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A solid solution to the problem--if this does not work as Jerry says you need a logic board. +

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I've been soldering the U28 chip on "fan on high" G4s for about a month now per Lemerise's instructions, and almost without fail it corrects the problem. I've salvaged about a dozen G4s so far. The hardest part is doing the procedure without accidentally destroying the machine, but using the fine-tip soldering iron Lemerise suggests, and a big magnifying glass (preferably one on a stand, and with its own light), it is possible to get pretty good at it.

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rdklinc, I'm glad you salvaged so many ibooks with this method. It's a easy repair, well easier than the infamous ibook G3 GPU chip issue.

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+ Great answer, lemerise! Glad to know I'm wrong about needing a new board. :)

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While my experience is with Windows-based machines, the basic hardware is very similar and still follows the same (or very similar) startup sequences. With that in mind, it sounds very much like the mother/logic board is dead. Power may be going through the board, but it's not powering the BIOS. This means either something between the power supply and the BIOS died, or the BIOS itself died. Either way, you're looking at a new logic board.

If you know cars at all, consider this: if the power button is the ignition switch, the BIOS is the starter motor. Turn the key and the lights come on, but the starter won't budge, so the engine can't turn over. Same basic concept. Unfortunately, you can't just replace the BIOS as easily as you can a starter...

Unfortunately, it's a bit late now, but a faulty hard drive won't cause a problem like this. Take the drive out and it should still attempt to boot. If this is not true on Macs, it's because Apple made it that way by design...but I find that more than a little unlikely.

I truly hope someone else has a better answer than that...but based on experience, it's a pretty classic symptom.

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Great analysis! Lemerise's response is almost definitely the specific answer to what is wrong with the board, but short of that, I like your logical breakdown of the situation. Thanks

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chris will be eternally grateful.
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