Hi people new here. I too have the same or similar problem. I inherited this 2001 Mac Powerbook G4 M8407 with broken hinges initially. I took it apart to remove the display and hopefully consider replacing hinges. After the fact I was going to purchase used hinges and replace them, but almost to costly when I got a complete used for parts unit. I was able to get the original unit working with the display screen removed using external monitor. I have subsequently installed used display screen complete with hinges and now find that the same thing people are describing here happening to me. I can get the laptop to work using external monitor but only have white screen display on OEM display screen, I can however control the brightness, so not sure what the logic board or inverter looks like or where it is?
Hopefully someone else can help as well.
Thanks,
Ron