1.Fuse is on the VCC trace that goes to pins C3,C4,D3 of the MAX8839L power ic.
2.Iphone 4g charging manager is
CSD75202W15 => "75202" near socket connector
4.try chagne this ic its CSD75202W15 => "75202"
Its protect usb power -5V
iphone 4 power management ic