iBook G4 trouble: won't stay awake

Discussion in 'PowerPC Macs' started by mab87, Nov 1, 2009.

  1. mab87 macrumors newbie

    Nov 1, 2009
    Hi! I could really use some help solving a problem I'm having with an iBook G4 (1.33 GHz) that I'm trying to fix for a friend. I fixed the two original problems but a new (much worse) problem has developed and I'm stumped as to what the cause might be. I've searched around and haven't found anyone reporting quite these symptoms (except possibly one post here about two years ago, with no resolution), but I hope maybe someone can either recognize the problem or perhaps offer some educated guesses that might be of help.

    What's happening now is that the computer seems to boot up (into OS X 10.4) normally, but after less a minute it just goes to sleep. Always. Plugged in and with or without the battery present. It's only after completing the boot sequence though. If I hold down Option to get the boot selection screen, the computer will sit there forever just fine.

    If I wake it from this state (by pressing a key), the screen comes on, but then the backlight goes out almost immediately. (It does come on briefly, and I can see that the screen is still displaying the desktop by shining a light on it.) However, the keyboard and trackpad are non-functional. The computer is not frozen -- pressing the power button pops up the Restart/Sleep/Shut Down dialog, but I can't do anything more.

    Then, after 30 seconds it goes to sleep again. Actually, 32 seconds from when I hit a key. Every time.

    I cannot figure out what kind of hardware failure could cause such a problem, besides possibly the PMU, but I've tried reseting it several times. I've tried booting from another (working) iBook G4, set up in Firewire target mode, and the exact same thing happens. (It also won't boot from the OS X install disc, but neither will the other iBook, so maybe the disc is bad, though I used it with my Cube not long ago.)

    Some further background: When I was given this computer, the symptoms were a flaky hard drive (not spinning up or not staying spun up) and extremely weak wireless. The hard drive actually works perfectly in an external case (at least, it never failed for me), and the wireless works with the new antenna. But I'm concerned that maybe I caused some damage when I was doing the antenna replacement (which is joined in an assembly with the inverter cable), as that's when the current symptoms started. Everything seems to be working for that first 60 seconds, though, and the timing is so regular -- what could cause that behavior?

    If anyone has seen this, or has some suggestions as to what might be at work and (ideally) how to fix it, I would be very grateful.
  2. pvmacguy macrumors 65816


    Sep 2, 2009
    Hmm I would take apart the LCD assembly and have a look around and make sure the connection to the inverter board is plugged in nice and tight. If it is then its possible that board has failed. BUT... From what you describe about the un-responsiveness and also the shutting off after a short period of time makes me think the logic board. A genius at the apple store once told me "if its highly ill-logical, its most likely the logic board."
  3. mab87 thread starter macrumors newbie

    Nov 1, 2009

    Turns out it was totally logical, pvmacguy. I just didn't see the pattern until last night.

    I first tried disconnecting the inverter cable from the logic board and the computer no longer went to sleep (but, of course, there was no backlight). I then separated the new antenna from the inverter cable (they come as assembly held together with some tape to protect the cables from the hinges), put back in the old inverter cable and the new antenna, and everything works! Hurray!

    Just then, I knocked a couple things off the table and out fell the bag the part shipped in. I picked it up to put the problematic cable back into and noticed... tiny shards of glass or plastic. Then I looked at the cable and discovered that (and I don't know how I didn't see this before) the "outboard" component attached to the inverter cable that fixes to the side of the screen was smashed, likely in shipping.

    Then the "eureka" moment: I didn't recognize the type of component, but it was labeled S1 -- a switch. Then I recalled the magnet on the underside of the upper case, corresponding exactly to the location of the component in the screen, and it hit me: This is the lid switch that is damaged, and it was probably telling the computer that the lid was closed, which caused the OS to put the computer into sleep mode at the earliest opportunity.

    That's it. A bad switch caused the whole strange problem. Ugghh! Well, I somehow feel better now, not just having fixed the problem by putting in the old cable, but actually understanding the cause and the symptoms. And I'm certainly pleased to have the computer fully functional again (and especially pleased that I didn't break my friend's computer in my attempt to fix it).

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