Fixed Powerbook G4 backlight - read how

Discussion in 'PowerPC Macs' started by petervee, Dec 22, 2009.

  1. macrumors newbie

    Joined:
    Nov 25, 2008
    #1
    Warning: If you dont know what you are doing, don't attempt this! You could destroy your laptop. Do it at your own risk.

    I have many Macs one of which is the Powerbook G4 12" Aluminum. Recently the backlight died. I opened it and started looking around for the reason. I have a background in computer design.

    I found that the backlight connector has four wires.
    Red: +V
    Black: Ground
    Green: Must be High (+5V) for light on/low for light off (turns inverter board off and saves power).
    Yellow: Steps of brightness (up to +4V).

    I realized that there was no 12V coming on the header (the red wire had no 12V).

    I pulled the backlight connector from the motherboard (the connector is right next to the fan). I stripped the fabric cover off the backlight cable harness to expose the four individual wires and then I cut the red wire 1" away from the header, and soldered a wire from the power supply board to this red wire (going to the backlight), and insulated all the connections and the bit of red cable hanging from the old connector. I plugged the connector back to the motherboard. Now three wires go the motherboard and the fourth (the red one) goes directly to the DC-to-DC Power supply. The 12V power supply spot on the DC to DC power supply board is not indicated but is the one, counting from the left, that is not labelled (there are four pins carrying 12V) in the row of power connections (the others are 24V, 3.3V, 5V etc).

    Voila! The backlight works fine again. No need to spend money on a new motherboard or backlight board.

    It pays to look around first before spending money and getting new boards.
     
  2. macrumors 68000

    lamina

    Joined:
    Mar 9, 2006
    Location:
    From Canada, living in Seoul
    #2
    Cool story bro. Did you happen to take pictures during the process?
     
  3. thread starter macrumors newbie

    Joined:
    Nov 25, 2008
    #3
    No photos yet

    No, I didn't take photos, as I remembered to do so after closing it - too late. Will do so next time I open it.
    Peter
     
  4. macrumors newbie

    Joined:
    Jan 13, 2010
    #4
    I just did this last night on a 12" powerbook whose backlight died over the summer! I just used a single strand of an old floppy drive cable, soldered to the DC-DC converter and tightly wrapped (and taped) to the red pin of the inverter cable.

    It works!

    However, as the OP states--don't try this unless you know what you're doing and/or take full responsibility of the risk you are putting your laptop in!!

    I took a couple pictures, here's the overall picture (before I cut the wire to length or taped it up). Click for full size:

    [​IMG]

    and here's a closeup of the pin I soldered to on the DC-DC converter board. Again, click for full size:

    [​IMG]

    Thanks for providing me the impetus to do this & revive my old PB!
     
  5. macrumors 68040

    NewMacbookPlz

    Joined:
    Sep 28, 2008
    #5
    Nice bit of advice, definitely a cheaper fix if you have the capacity to do the work instead of purchasing new parts!
     
  6. DaKuLo, Nov 19, 2010
    Last edited: Nov 19, 2010

    macrumors newbie

    Joined:
    Nov 19, 2010
    #6
    Backlight Troubleshoot

    I know this is an old thread, but I'll give it a try anyway.

    I'm trying to duplicate Petervee's procedure below, but when I get to locating the backlight cable, I'm not sure which fan it is near (RT of LFT)? It would help to have a picture. Then I'm wondering how to check for the voltage and where I connect directly to the proper 12v DC source?

    It would be awesome to get my old G4 back in service.

    Any help would be appreciated.

    BTW My PB is a 17in, if that makes a difference.

    Petervee said:


    I found that the backlight connector has four wires.
    Red: +V
    Black: Ground
    Green: Must be High (+5V) for light on/low for light off (turns inverter board off and saves power).
    Yellow: Steps of brightness (up to +4V).

    I realized that there was no 12V coming on the header (the red wire had no 12V).

    I pulled the backlight connector from the motherboard (the connector is right next to the fan). I stripped the fabric cover off the backlight cable harness to expose the four individual wires and then I cut the red wire 1" away from the header, and soldered a wire from the power supply board to this red wire (going to the backlight), and insulated all the connections and the bit of red cable hanging from the old connector. I plugged the connector back to the motherboard. Now three wires go the motherboard and the fourth (the red one) goes directly to the DC-to-DC Power supply. The 12V power supply spot on the DC to DC power supply board is not indicated but is the one, counting from the left, that is not labelled (there are four pins carrying 12V) in the row of power connections (the others are 24V, 3.3V, 5V etc).

    Voila! The backlight works fine again. No need to spend money on a new motherboard or backlight board.

    It pays to look around first before spending money and getting new boards.
     

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