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My PowerBook G4 is broken and has been for a couple of months now. I owned it while it was working for about 1 and a half years. When it broke originally, I was restarting it after changing the boot logo in the system files and when it rebooted, it just stopped at the bright blue screen that I'm pretty sure comes right before the grey apple logo on a grey background. I left it for a while and it never finished booting. So I restarted it again and the same thing happened several times.

I then opened up the RAM removal door and saw that there appeared to be slight decay to one of the sticks of RAM. This may or may not be a problem. I removed the RAM and started it and the computer beeps as it should when it doesn't find the RAM when I put the RAM back in, the computer makes the chiming noise, but the screen does not turn on anymore. (By this I do mean that no part of the screen is lit. No backlighting occurs and pixels remain dead.) This is strange because before I removed the RAM, the screen turned on but stopped at the blue screen.

I also attempted hooking the computer up to another Mac via FireWire and repairing the hard drive. I then got a USB and put Leopard on it. I cannot boot from the USB either.

I have tried all of the obvious including resetting PRAM and resetting PMU. Neither of these had any effect on the computer at all. I even tried removing the main battery and letting the backup battery charge over night snd that also had no effect on the starting of the computer. I also tried hooking it up to a Mac display and that did not work either. That test may be unreliable, however, as I have not confirmed that the display itself works as I do not have the appropriate cables.

I am now at a point where I have the computer where it boots up, chimes, but the screen never turns on. I have the Leopard install image on a USB drive, and the hard drive is repaired. (Disk Utility said that it was corrupt and I repeaired it in Disk Utility as well.) I do not need the files that were previously stored on this computer. It previously ran OSX Leopard. Any other ideas on what I could try or what could be going wrong here?

I have previously thought about it being a Logic Board issue and this seems to be agreed by first answer I got. Are there any steps I can take to isolate whether or not it is the logic board? Is there any easy way to fix or replace it?

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Paragraphing might help –  revolver Mar 11 '13 at 4:29
    
Paragraphed. Apologies for the bit the entire thing being in code blocks. I wrote it on mobile and I guess that's what the tab does! Thanks for fixing that! I have added more information based on feedback I received in the first answer. –  cbbcbail Mar 12 '13 at 3:41
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up vote 1 down vote accepted

I would respond with this as a comment but I don't have that option, assuming because my reputation hasn't yet reached 50.

To me this sounds like a couple of possibilities. I don't see mention of whether or not the screen gets backlight, only that "it doesn't turn on", so I'm writing this assuming that the computer chimes but the screen remains black. It's good that you've tried reseating the RAM however I would also try to isolate both DIMMs. Remove one of the RAM DIMMs, try powering on the Mac. Reinstall the removed DIMM and remove the other DIMM, try powering on the Mac. Try installing the DIMM from slot 1 into slot 2 and vice versa. See if there is any change in behavior after each of these changes. If the issue persists with each change then RAM is unlikely to be the culprit.

Assuming RAM isolation has no effect I would try resetting the PMU. You didn't mention the exact model of your PowerBook G4 but this Apple KB article should help you identify the correct process for your computer. PMU resets typically have results when the Mac simply isn't power on at all however I've seen them resolve "no video" issues as well in the past.

If both of these had no effect I would start looking at it as a hardware failure, with either the logic board or LCD/display assembly to blame. You did mention that an external display had no video as well so I would lean towards a logic board failure. I would find it odd that the failure occurred after reseating the RAM but it could be a coincidence.

Also, PowerPC based Macs (G3, G4, G5) typically will not boot from USB devices. There ARE some methods for getting some specific models to do so however they often come with mostly mixed results. Your best bet for installing 10.5 would be doing so from a firewire drive or from the install DVD.

Hope that helps! Let us know if you have any luck with bringing it back to life!

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You couldn't have put all of that in a comment anyways. Thanks for your help! I have added more information to the question regarding things that appeared unclear to you. I hope this might help you add to your thoughts on my options. What are some steps to isolating the Logic board? I have previously tried resetting the PMU and nothing came of it. Thanks again! –  cbbcbail Mar 12 '13 at 3:39
    
@cbbcbail, It sounds like you have kinda isolated the logic board already by connecting an external monitor. When I have a no video or distorted video issue I will connect an external display to see if the issue occurs there as well. If it does then it's the GPU / video card / logic board. If the issue is isolated to the internal display then it's something in the display assembly. You might try again with another, known good, external monitor just to be sure. –  Mr Rabbit Mar 13 '13 at 13:53
    
in that case, what can I do to replace/repair the logic board? –  cbbcbail Mar 15 '13 at 19:26
    
Sorry about the late reply, was out of town for several days... Replacing the logic board is the only sure way to repair the problem, assuming the board is the culprit. However, several folks have had luck "re-flowing" their logic boards in MacBook Pros for similar issues. You might look at this process as the idea would be the same for PowerBooks: ifixit.com/Answers/View/9045/… –  Mr Rabbit Mar 22 '13 at 16:00
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