Backlight always turns off after 2 minutes of inactivity

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PowerBook G4 Aluminum 17" 1-1.67 GHz

Model A1013, A1052, A1085, or A1107 / 1440x900 screen resolution

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rdklinc @rdklinc

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Posted: Apr 24, 2011

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Backlight always turns off after 2 minutes of inactivity

Hello! Goofy question of the day: I've got a very nice 17" PowerBook, but the screen backlight without fail shuts off after about 2 minutes of inactivity. Again, I know it's only the backlight because it has a faint image. If I close the machine and open it up, the light comes back, then goes off again after 2 minutes of inactivity, and you have to either power off/on or close and open the machine to trigger it to turn on again. If you actively use the machine, it stays on indefinitely and you never notice an issue. Because this is not an intermittent problem and the backlight is reliable otherwise, I tend to think this is probably not a bad screen/inverter/cable, but more likely a sleep/reed switch/sensor issue of some type? It's got a fresh install of Leopard, and I've tried turning off all the power saving settings, so I know it's not an OS issue. I'm looking for ideas on where to start, given that this is not the typical "dead backlight, replace the inverter cable" problem. Thanks!

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mayer @mayer

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Posted: Apr 24, 2011

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I know this sounds simplistic, but is it doing the same with an external monitor. Just because a problem is different, don't forget the tests that we know work.

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I tried that, and the external display stays on when the backlight goes. Like I mentioned, it's only the backlight that goes out, not the video image, i.e. I can see a faint image and the computer continues to operate when the backlight is dark. I don't deal with these machines everyday, so I don't know exactly what I'm looking for, but I'm wondering if it's the equivalent of a faulty reed switch?

Apr 24, 2011 by rdklinc

Try booting up from a system installation disk to see if software might be involved in any way. There is no type of reed switch in the display. Does your keyboard have an ambient light sensor?

Apr 24, 2011 by mayer

Still did it booting from another drive, so it's not software. Actually, I just reset the pram and pmu, and it seems to be fixed! I'm accepting your answer because you reminded me to remember the simple stuff (which the resets certainly are). Thanks!

Apr 24, 2011 by rdklinc

Thanks for accept. I tend to forget the simple things sometimes when faced with tough problem. Sometimes all it takes is to voice the problem to someone else to see the solution.

Apr 24, 2011 by mayer

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I tried that, and the external display stays on when the backlight goes. Like I mentioned, it's only the backlight that goes out, not the video image, i.e. I can see a faint image and the computer continues to operate when the backlight is dark. I don't deal with these machines everyday, so I don't know exactly what I'm looking for, but I'm wondering if it's the equivalent of a faulty reed switch? — rdklinc
Try booting up from a system installation disk to see if software might be involved in any way. There is no type of reed switch in the display. Does your keyboard have an ambient light sensor? — mayer
Still did it booting from another drive, so it's not software. Actually, I just reset the pram and pmu, and it seems to be fixed! I'm accepting your answer because you reminded me to remember the simple stuff (which the resets certainly are). Thanks! — rdklinc
Thanks for accept. I tend to forget the simple things sometimes when faced with tough problem. Sometimes all it takes is to voice the problem to someone else to see the solution. — mayer