I think some others have this same or similar problem or variation.
My machine(500mhz)starts up fine, but the screen is totally dim , if you turn off all the lights and look at it in the dark you can see that everything is there. When you close the top , it goes into sleep mode perferctly , you can hear the sensor turn off and on, the sleep light pulses fine.
I bought a used backlight on ebay but I do not want to go any further
as far as taking apart as I do not know how to open up the top panel/screen panel to replace the backlight. It also looks like someone has been in there allready as a lot of screws are missing. where can I find extra scews? I am handy and think i can do it with your cd maybe? Or better yet how do i know if that is the problem? I cannot check to see if the machine will display on an external monitor because I need the adapter. gonna ask a friend to borrow his. If it works with the adapter and external monitor can it be safe to say that it is the backlight only? I also have another fully working ibook that works fine.