Since you get video on an external device the PB graphic card (logic board) should be OK. Now we need to troubleshoot the LCD display assembly.
First: use a flashlight or a lamp to lighten the white Apple logo on the display back panel and check if you see a faint image of the desktop onscreen. If so then you have a screen lightning problem. This can be caused by:
- disconnected or loose inverter cable connector to the logic board or to the inverter board.
- faulty backlight fluorescent tube (CCF lamp that lighten the LCD panel)
- in rare occasions: faulty inverter circuitry on the logic board
If you don't see a faint desktop image onscreen then the two sub systems (video and lightning) are failing (rare IMHO) and the LCD panel need to be replaced.
A TV set has less image resolution than an external LCD monitor that's why you don't have a good image quality. Connect the PB on a DVI external monitor and you'll get full quality.
Since you get video on an external device the PB graphic card (logic board) should be OK. Now we need to troubleshoot the LCD display assembly.
First: use a flashlight or a lamp to lighten the white Apple logo on the display back panel and check if you see a faint image of the desktop onscreen. If so then you have a screen lightning problem. This can be caused by:
- disconnected or loose inverter cable connector to the logic board or to the inverter board.
- damaged inverter cable (or reed switch board / cable, the PB display sleep system)
http://www.ifixit.com/PowerBook-Parts/G4-Aluminum-17-Inch-Inverter-and-Antenna-Cables/IF155-051
- faulty inverter board
http://www.ifixit.com/PowerBook-Parts/G4-Aluminum-17-Inch-Display-Inverter/IF155-048
- faulty backlight fluorescent tube (CCF lamp that lighten the LCD panel)
- in rare occasions: faulty inverter circuitry on the logic board
If you don't see a faint desktop image onscreen then the two sub systems (video and lightning) are failing (rare IMHO) and the LCD panel need to be replaced.
http://www.ifixit.com/PowerBook-Parts/G4-Aluminum-17-Inch-1-67-GHz-HR-LCD-Only/IF155-071