Powerbook G4 screen goes black randomly...

the power manager controls sleep as well as the brightness of the display. Sadly, i never found out what the solution was on my old iBook before I sent it in to get it replaced by my current G4 iBook (i had the 900Mhz G3, They gave me a 1.2Ghz iBook after my G3 went in 14x ) anyways, it sounds like the power manager is having problems.

I would say if it looks like it's still doing, what you do, is unplug the machine, pull the battery (save your data first before shutdown!) and press the CUDA switch (probably under the keyboard if it has one or something) and reset it is fully. If you have time, and can wait, let the system sit for 24hrs w/o power whatsoever.
It might be that the power manager did not fully reset itself if the LCD Backlight goes off again in the future.

if it still has warranty, and it continues to do it, call apple and let them know, it might be a hardware problem (most likely not, Apple just would rather replace mine that have me send it in for the 15th time)

Anyway, Good Luck!
Coius

I will try that if it begins to do it again. I really appreciate the info. I was really scratching my head!

-bigd

A potential cause for your problem is a bad reed switch and/or inverter cable. On the 12" PowerBook G4's and final rev of the iBook G4, the reed switch and inverter cable are two separate parts.

On the older iBook G4's, the reed switch and inverter cable were one piece - when it failed (which was a when not an if) the computer would do weird things - similar symptoms to what you are describing. Black screen but everything works fine. I would venture a guess that your reed switch is bad as the computer could be thinking that it's in clamshell mode and turning off the display. If there is no video on your lcd when this occurs - you've got a bad reed switch. If there is video - you've got a bum inverter cable.

Another thing to bear in mind. I'm a portable tech who has worked on just about every portable that Apple has ever made (save for the kanga g3) and I would say that the 12" PowerBook G4 is a machine that even the most seasoned of techs are wary of working on. You may be better off having your local Apple reseller/service dept handle this repair. It'll save time, aggrivation and risk of damaging anything when working on the computer.

I'm going to assume you are no longer under warranty. I'd advise checking with apple on this before making any decisions. If you have it sent in for depot repair, you will be looking to spend at least $400 as this would be considered a tier 1 repair. If you take it into a local apple reseller with a portable certified tech, you'll be looking around $250 or so. (the parts are under $40, it's almlost pure labor)

Thanks for the insight. I have done some reading and asking other people and the reed switch issue has come up. I bought this powerbook second hand and for a really good price. I have worked on other various types of electronics before (hearing aids, built and repaired PC's/laptops, etc.) so I think I am going to risk it and try to change the reed switch. I do appreciate the advise however (got a eally good deal from ifixit.com). Plus I think it will be kind of fun to try and do it. If I end up blowing it up I end up blowing it up and it would give me a great excuse to upgrade, ha.

I will say that this forum is by far the most helpful in terms of hardware/repair help. You guys really know your stuff. I appreciate the advise! I will let you know how it goes.

Again, many, many thanks!

BigD

I was still having the same problems listed above with the addition of when I close the lid and put the computer to sleep, then open it back up , the screen flashes the current screen then goes back to the dark thing again. So I tried to replace the reed switch to no avail. Problem still persists. I also have a new inverter in my presence. My new question is where exactly does the inverter sit on the 12" 1.5 PB? I assume I would have to pretty much COMPLETELY dismantle it to get to it. Any thoughts?

-BigD

On the aluminum powerbooks (12, 15, 17), the inverter is inside the metal hinge cover.

Hi- I'm currently having the same problem with my wife's 12" 1Ghz powerbook. The screen stays on variable lengths of time from seconds to minutes before going dark. I am interested to hear if you have found any sort of solution. I have tried booting off of a recent disk warrior disk and the problem persists making me think this must be hardware. Bummer.
Many thanks if you can give me some guidance.

Scott

There must be something in the air! I've been having the same problem for about a month. Putting the computer to sleep and then waking it has been working, more or less. But today it's been almost impossible to work.

My local technician suggested the computer thought the clamshell was closed (is this the reed switch?) but I've got an external monitor attached and Profiler shows the clamshell as open. Now my technician thinks it may be the logic board.

If anyone has suggestions on what to try first, I'm all ears!

Roddie Grant

I have no idea how this might fit in, but I have noticed that the length of time the screen stays bright is significantly shorter if I have a CD in the internal drive even if it is not currently being read from. I get no more than a couple of seconds of bright time vs minutes without a CD in the drive.

So get this. I hadn't had enough time to adequately replace the display inverter and now that I updated to OS X 10.4.9 it works perfectly fine... no problems with the display whatsoever since the update. Is this a coincidence? In any event I am not going to replace the display inverter until it acts up again.

-BigD

The 10.4.9 update did include ATI and nVidia drivers. You might have been having issues due to a bug. Let's hope that's all it was.

Mine does the same thing, but it happens when I am using the keyboard, usually when I am pressing the shift or command key and some other key. It's random, and I know the computer is not off because I can see a faint light source glow on the keyboard. and, for example, the Number Lock light will illuminate on and off when I touch the F6 key, but nothing will "wake" it. Even the Force Restart key command won't work. I have to restart it by holding the power on/off button down for a few secs (then I can see the screen go 100% black), then power back up again. I had the keyboard replaced by MacEdge in Nashua, NH last October, at the same time I had them install a new and larger hard drive (tried to do it myself like a fool and bent the keyboard!) so maybe there is some connection there. Although I think it was doing this now and then even before the new keyboard.

Hi, for a while now I've been trying to figure out what causes my PowerBook G4 17" screen to fail. You know how on PCs, specially older ones, you can only see the picture square on? Meaning, if you try and see it from the side you get kind of a negative black on the dark areas? Well this is what my powerbook screen is doing now, but only from one side. If ilook at it at an angle from the left it looks great, but from the right, the dark areas become "negative"... This screen was replaced due to dead pixels so it's actually a new screen, but the mac is not under warranty anymore. I was wondering if replacing the inverter board could fix this?
Thank you very much!

My G4 PB 1.33ghz 15inch does the same...after wakin up it stays on for a few seconds and then the screen goes dark again....
did you find out by now what caused the problem?
was it hardware or was it the pmu management?
any advive would be apreciated...

My G4 PB 1.33ghz 15inch does the same...after wakin up it stays on for a few seconds and then the screen goes dark again....
did you find out by now what caused the problem?
was it hardware or was it the pmu management?
any advive would be apreciated...

My G4 PB 1.33ghz 15inch does the same...after wakin up it stays on for a few seconds and then the screen goes dark again....
did you find out by now what caused the problem?
was it hardware or was it the pmu management?
any advive would be apreciated...

My G4 PB 1.33ghz 15inch does the same...after wakin up it stays on for a few seconds and then the screen goes dark again....
did you find out by now what caused the problem?
was it hardware or was it the pmu management?
any advive would be apreciated...

My PB G4, 17", 1GHz has had this problem for a while, although intermittent. I usually use the "close the lid" routine to get my screen back, usually with success. Once back it usually stays on - at least for a good while. Having said that, since connecting my iPhone its got worse, usually when syncing. Same problems with CD/DVD disks, as soon as they load up the screen goes. I have used screen sharing from from my work MacBook to access it when the screen is black and have total access and usability. Anything you guys can offer to help would be greatly appreciated.

Dave M, UK.

So I updated to 10.5.1 and still was having no issues. I then did the subsequent 10.5.2 update and the bug started to occur again. So I wiped the hard drive and reinstalled 10.4 and the problem was still there. Subsequently updated to 10.4.11 and it's been functioning 100% perfectly. I ran tech tools and AHT during each of these OS versions and it always came back ok. So I truly believe this is a glitch with the integrated graphics and subsequent updates.

Hope this helps.

-BigD

Came across this great thread after experiencing the same blackscreen problem on my PB G4 1Ghz running 10.4.11. In my case, the laptop worked fine but the screen was 95% dark from startup and rebooting didn't correct this, as it has in the past. (95% because if I squinted hard I could see things on the laptop screen).

I have an external monitor so I could soldier on with only one screen ;-), but I was fearing the worst for my poor G4, like the backlight was dead, maybe.

Anyhoo, I opened the Display preferences and started playing around with the screen that was presented on the ext. monitor. Nothing happened. Then I squinted at the laptop screen and saw that a second Display pane was showing there, which I dragged over to the external. It was the Display pane for the laptop screen. The brightness slider was pulled all the way over to dimmest. Like me I guess. Sliding it to 'brightist' solved the problem.

In my defense the F1 and F2 keys on the laptop keyboard, which normally control screen brightness, have been remapped, so the laptop screen can't be dimmed by random accidental arpeggios on the keyboard. I think it was one of my cats getting back at me for reducing the Friskies rations.

Yeah, I'm lame, I know. But that's how the problem got diagnosed and solved.