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View Full Version : Fixed Powerbook G4 backlight - read how




petervee
Dec 23, 2009, 01:58 AM
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.



lamina
Dec 23, 2009, 04:01 AM
Cool story bro. Did you happen to take pictures during the process?

petervee
Dec 28, 2009, 10:54 AM
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

IronRooster
Jan 13, 2010, 04:37 PM
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:

http://greenrootsphoto.com/files/12_pb_inverter1_t.jpg (http://greenrootsphoto.com/files/12_pb_inverter1.jpg)

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

http://greenrootsphoto.com/files/12_pb_inverter2_t.jpg (http://greenrootsphoto.com/files/12_pb_inverter2.jpg)

Thanks for providing me the impetus to do this & revive my old PB!

NewMacbookPlz
Jan 13, 2010, 05:44 PM
Nice bit of advice, definitely a cheaper fix if you have the capacity to do the work instead of purchasing new parts!

DaKuLo
Nov 19, 2010, 04:44 PM
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.