g4 1.42 14" with dark screen new inverter...

thehumble1 · Jun 16, 2007

I got a cheap 1.42ghz 512mb RAM, 14" screen G4 ibook because it had a broken hinge. I tore apart the laptop and replaced the hinge (screen frame) and put it back together. The screen wouldn't work. I opened it back up and found that the video connector was lose, so I connected it and put it back together. BAM!! Everything worked... everything except the sleep feature when the lid is closed. So I opened it back up, took the magnet from the old frame and put it on the new frame (which was missing its magnet).

When I turned it back on the screen was blank/dark. It showed all the signs of classic inverter board burnout (dark screen, can be seen with flashlight from behind, can be seen on external monitor), so I ordered an inverter board and when it arrived, I swapped it out. Still nothing. The next idea would be the backlight, but that doesn't make sense... I'm trying to figure out what might have happened to make the inverter/backlight go from working fine to not working when all I did was removed the screen back case, screw on the magnet and close it up. I have done a bunch of digging around under the hood and am wondering if anyone knows of a possible ground wire, other connection, easily broken wire, or other issue that might have happened. I'm thinking that it might be one of the power wires that goes into the inverter. It might have broken inside the shield, or maybe I was sold another bad inverter board.

So:

Assumption 1: one or both inverter boards are good.

Are there any connections other than the inverter data/power cable from the mobo and the cable from the inverter to the backlight?

Does anything else (backlight, etc) have to be grounded? Where are these groundings?

Would anything else give the same symptoms except the inverter?

How can I test the backlight? I heard that there are two lights in these machines, so if it was one of the florescent lights, only 1/2 the screen would be dark.

Assumption 2: Neither board is good and that is the problem.

How can I test the inverter board (short of an osilascope) to see if it's working?

Is this a good assumption?

I'm about stumped right now and haven't found any direct help on forums. I'm hoping someone in the Mac community has run into this or has an idea about what could be going on. I'm really hoping that I missed something like replacing a screw that is also a ground or something along those lines. Thanks for any help you can give.

cwa107 · Jun 16, 2007

thehumble1 said:
I got a cheap 1.42ghz 512mb RAM, 14" screen G4 ibook because it had a broken hinge. I tore apart the laptop and replaced the hinge (screen frame) and put it back together. The screen wouldn't work. I opened it back up and found that the video connector was lose, so I connected it and put it back together. BAM!! Everything worked... everything except the sleep feature when the lid is closed. So I opened it back up, took the magnet from the old frame and put it on the new frame (which was missing its magnet).

When I turned it back on the screen was blank/dark. It showed all the signs of classic inverter board burnout (dark screen, can be seen with flashlight from behind, can be seen on external monitor), so I ordered an inverter board and when it arrived, I swapped it out. Still nothing. The next idea would be the backlight, but that doesn't make sense... I'm trying to figure out what might have happened to make the inverter/backlight go from working fine to not working when all I did was removed the screen back case, screw on the magnet and close it up. I have done a bunch of digging around under the hood and am wondering if anyone knows of a possible ground wire, other connection, easily broken wire, or other issue that might have happened. I'm thinking that it might be one of the power wires that goes into the inverter. It might have broken inside the shield, or maybe I was sold another bad inverter board.

So:

Assumption 1: one or both inverter boards are good.

Are there any connections other than the inverter data/power cable from the mobo and the cable from the inverter to the backlight?

Does anything else (backlight, etc) have to be grounded? Where are these groundings?

Would anything else give the same symptoms except the inverter?

How can I test the backlight? I heard that there are two lights in these machines, so if it was one of the florescent lights, only 1/2 the screen would be dark.

Assumption 2: Neither board is good and that is the problem.

How can I test the inverter board (short of an osilascope) to see if it's working?

Is this a good assumption?

I'm about stumped right now and haven't found any direct help on forums. I'm hoping someone in the Mac community has run into this or has an idea about what could be going on. I'm really hoping that I missed something like replacing a screw that is also a ground or something along those lines. Thanks for any help you can give.

I once had a customer with an Alienware laptop that had no backlight. I replaced his inverter and found that it didn't fix the problem. Then, I replaced the CCFL backlight tube, and that didn't fix the problem. Then, I replaced the entire screen assembly - and that didn't fix the problem. As it turns out, that particular model of laptop had a problematic power management system that stemmed from a bad design in the motherboard itself.

The moral of this story is that you can easily go on a wild goose chase with these things. Typically, the CCFL tube has a very long life (typically 10,000 hours+), so if you know the history of the screen and it hasn't been left on for hours on end, it's probably just a bad replacement inverter.

dtravis7 · Jun 16, 2007

Also are you sure all the plugs are in solid? Any wires get pinched? Any wires flexed enough to maybe break? It's possible both inverters are bad but....

do you have just one screen with one backlight?

Is the brightness turned up on the iBook? So easy to bump F1-F2 sometimes and turn it off. Done it here on my iBook.

Most of the systems I have repaired with no backlight were the Inverter but 1-2 times it was the CCFL tube (Backlight).

cwa107 · Jun 16, 2007

dtravis7 said:
Also are you sure all the plugs are in solid? Any wires get pinched? Any wires flexed enough to maybe break? It's possible both inverters are bad but....

do you have just one screen with one backlight?

Is the brightness turned up on the iBook? So easy to bump F1-F2 sometimes and turn it off. Done it here on my iBook.

Most of the systems I have repaired with no backlight were the Inverter but 1-2 times it was the CCFL tube (Backlight).

I totally agree with your assessment. The flex cables are very easily damaged or dislodged. Follow the flex cable from the back of the LCD to the systemboard and make sure it's undamaged (not kinked) and well-seated. I should have mentioned that.

bryphotoguy · Jun 16, 2007

If it's just a power management issue, you should be able to do a PRAM reset to restore power evenly to factory defaults.
If you've replaced both cables and are still having a problem, I have no clue what to say besides replace the whole screen and everything.
Sorry I can't be of more help.
Bryan

dtravis7 · Jun 16, 2007

Forgot one thing but your messing with that Magnet made me remember. A friend bought a used iBook. It worked great till one day the screen went dark. He messed with it for days and it was something to do with the magnet and that reed switch in his case. His would sometimes light if he almost closed the lid. I will ask him later what he did to solve it just in case.

thehumble1 · Jun 18, 2007

a few more things

WOW, thanks for all the feedback so far. It's giving me a lot more to check on at least. bryphotoguy, I have done about 4 PRAM resets, which have, of course, not done anything. I've also followed the cables around a bunch, but think that is probably where the problem is. It's about $49 for a new set of inverter cables, but that might be the next step, either that or jump each one individually to test.

What makes me think it is a cable or ground somewhere is that it happened when I opened the case up, not just through usual use. That makes me think that the inverter going out instantly (and just when I happened to open up the case) and the new one being bad as well is a long shot (but one i'll check later). I think for now, I am going to figure that one of the wires got pinched in the reassembly process and is broken inside the insulation. I'll check for pinches and nicks in the insulation of both the inverter cabling to the system board and to the backlight (CCFL).

dtravis7, I think that is common with g3s as they have a reed switch/inverter cable. My reed switch is completely separate, though it might be intimately connected to the backlight somewhere on the motherboard. I don't know if it would give me that same symptom, but I like where you are going with it. If it's a true magnetic switch I need to figure out if it is closed or open at rest (without magnet present), then I could jump the switch or pull off a lead to make sure the switch isn't stuck... I thought about this earlier, but because the reed switch isn't part of the inverter cable harness, I left it there.

I want to try a bunch of stuff before I ask my girlfriend if I can swap parts out with her good g4 12", to test. I'd hate to have two dead screens on my hands. What sickens me is that the fix went superb, with a system board solder, a broken wire solder, and a lot of patience put into it so far.

Thanks again for the help... I've got new hope