iBook G4 and Backlight problems

[coius]

Hi, I recently got the task of fixing my friend's iBook G4. These are the symptoms:

Machine turns on.

Backlight comes on for 1/5th of a second, then turns off. does this whether it does to FireWire Target Disk Mode, Open-Firmware, or regular boot.

What has been done:

PRAM Reset

Power Manager reset

Reset done from Open-Firmware

I have even pulled the battery when I did the PowerManager reset.

Oh wise people on the board. Do ANY of you have a solution or something to set me in the right direction?

I can verify the rest of the system screen works. I can see the stuff on the screen (though it is very dim), and I am at a loss. I am going to do a bit of googling and see what I come up with. Hopefully this doesn't require something like a new backlight or invertor board, but if it goes down to that, I can do it. I already worked on it before...

 

[Franklinstein]

That sounds less than pleasant. It's not a problem I've seen.

Most of the iBook display problems not directly related to the GPU typically have something to do with a worn cable, or a bad display component. Since the light flickers for a second, it's probably not the cable. If you've got a spare, try swapping over a different screen and see if the new one works.

There are a few Open Firmware tricks out there that may affect your backlighting if done improperly. One example would be the display spanning hack.

 

[foetoid]

I would try re-seating the cable for the backlight, and also the backlight itself may need to be replaced. I don't know if they have replacement bulbs available for the iBooks or not. Last time I was changing them out was on some old POS systems that were running Windows 98. But, I would try the cable first as it will probably cost next to nothing, then move to the backlight if you're still without success and then, if still no progress, I would probably just try a new display all together. The issue is definitely with the display itself. You can narrow it down to the display cabled, or the backlight inverter board, or the backlight itself. Honestly I would probably lean toward the inverter board if it's flickering on and off again. Either loose connection or a bad board.

 

[coius]

I would try re-seating the cable for the backlight, and also the backlight itself may need to be replaced. I don't know if they have replacement bulbs available for the iBooks or not. Last time I was changing them out was on some old POS systems that were running Windows 98. But, I would try the cable first as it will probably cost next to nothing, then move to the backlight if you're still without success and then, if still no progress, I would probably just try a new display all together. The issue is definitely with the display itself. You can narrow it down to the display cabled, or the backlight inverter board, or the backlight itself. Honestly I would probably lean toward the inverter board if it's flickering on and off again. Either loose connection or a bad board.

I talked to my friend and am going to get a new inverter. I doubt it's the cable. It doesn't affect if it I push on anything, or if I move the screen.

I tested voltage on the inverter. There is voltage and power going in. None going out to the display. I am going to try replacing that. Anyone know how much voltage is supposed to go the display and what is supposed to go the inverter from the board?

Would help if I could pinpoint at what point it fails. I am really guessing the inverter, since zero power goes to the display...

 

[Christopher]

My iBook on the 5th day I had it got coke spilled in it and after i cleaned it and let it sit for an hour or 2, the backlight would fade on and you could bend SLIGHTLY the display and the backlight would change spots and it was lighting. I left it off over night with battery and power out and the next day it was fine.

 

[coius]

I ordered another inverter. It should be here by the end of next week. Let's hope it does the trick!!!

 

[harofreak00]

I joined soley to see if this problem has been fixed. I am having the exact same issue with my G4. The display flashes for a second when first booted, and will flash on when I change the display resolution.

Seen here:



I am wondering what you did to fix it.

 

[harofreak00]

I replaced the LCD inverter today, and it works great!

 

[tomlee59]

Congrats -- well done!

Generally speaking, if the tube lights to more-or-less normal brightness, but then goes dark, suspect the inverter. It's common for the insulation on the transformer's windings to break down. That causes excessive drive current, and a subsequent shutdown as protective circuits engage. These transformers are designed with very little margin (to keep them small), and it's a miracle they work as long as they do.

A typical peak output voltage in steady state might be a good piece of a kilovolt (several hundred volts rms; roughly proportional to CCFL length). To start up, the striking voltage might be 1.5x as high. So there's a fair bit of stress on the insulation of those tiny windings.

 

[coius]

Sorry about that. I sent an email back to the guy after he eMailed me and I told him the inverter fixed the issue. Thanks for reminding me to come back to it! Glad it worked out!

Iirc, this was the last reason my iBook G3 went in and I got the G4 iBook. It was because the screen would randomly turn off. Now that I look back on it, the 14th time (and final) time the machine went in and the reason Apple sent me a G4 was because of the inverter failing. That's why I now have a G4 iBook (well... I traded it to my friend and I got a MacBook I purchased through I loan from another friend)