For 3GS I found two possible fixes for that problem!
1. "'''I fixed my backlight issue on iphone 3GS'''" (Jason Simmons replied 4 months ago) - http://getsatisfaction.com/apple/topics/iphone_back_light_wont_work
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I did the same thing. Got mine wet in the lake and got back and backlight did not work. Took it apart and got what water was left out. Put it back together. Phone worked but no backlight. So I decided to take it apart again as a last ditch effort a couple of days later. Wallah!!! I fixed it.
Here is how I got my backlight back to working.
You have to take about your iphone. There are instructions on the web to do this. Disconnect plugs 1 and 2 and ribbon 3. I had to remove number 5 cover cafefully. It will pop off. See the image. Just above the pointed out area of the coil, there is a small area of circuity. Mine had just a little bit of corrosion. Had to look hard to see it. I took a toothbrush with some contact cleaner and degreaser. Cleaned all the corrosion off. Put the cover #5 back on and both plugs and ribbon. Put the 2 screws back in the bottom. Pressed the button and top and low and behold, my backlight was on.
I found two possible fixes for that problem!
1. "'''I fixed my backlight issue on iphone 3GS'''" (Jason Simmons replied 4 months ago) - http://getsatisfaction.com/apple/topics/iphone_back_light_wont_work
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I did the same thing. Got mine wet in the lake and got back and backlight did not work. Took it apart and got what water was left out. Put it back together. Phone worked but no backlight. So I decided to take it apart again as a last ditch effort a couple of days later. Wallah!!! I fixed it.
Here is how I got my backlight back to working.
You have to take about your iphone. There are instructions on the web to do this. Disconnect plugs 1 and 2 and ribbon 3. I had to remove number 5 cover cafefully. It will pop off. See the image. Just above the pointed out area of the coil, there is a small area of circuity. Mine had just a little bit of corrosion. Had to look hard to see it. I took a toothbrush with some contact cleaner and degreaser. Cleaned all the corrosion off. Put the cover #5 back on and both plugs and ribbon. Put the 2 screws back in the bottom. Pressed the button and top and low and behold, my backlight was on.
Hope this helps you guys
http://s3.amazonaws.com/satisfaction-production/s3_images/222474/iphone_inline.gif
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2. '''iPhone 3GS No Backlight Fix''' - http://blog.techsick.com/guides-tutorials/iphone-3gs-no-backlight-fix/