The attached pictures should help explain the backlight circuit of the 3G phone. The schematics are from the NXP Power Controller user manual - link to it here:
http://people.openmoko.org/tony_tu/G...50633DS_02.pdf
Many thanks to NXP for releasing it to the public.
The iPhone backlight circuit would seem to be a mix between Fig. 30 and 32 - there appear to be a component (I labelled it FET?) that combines at least one FET and possibly a second FET or diode.
I don't have the connections to the NXP power control chip shown on the board layout, but the schematics give the pin designations, and the NXP user manual gives the pin numbers. The word "GND" denotes a ground connection (it's hard to read text on the jpg image).
This contradicts the postings from Sassaki, but I have checked my board layout carefully.
Hopefully this will help everyone with 3G backlight problems be able to trace the source.
I can't get manage attachments to upload the images, so I have used links to them, if they aren't clear or working let me know:
http://loadmypic.com/server1/out.php...GBacklight.jpg http://loadmypic.com/server1/out.php/i65621_Sch1.jpg http://loadmypic.com/server1/out.php/i65622_Sch2.jpg