Iphone 4 no Lcd Light & Logo Solution Jumper Problem Ways iphone 4s display problem in iphone 4 can be due to lcd connecter pin broken damage and due to water damages.
in case of light problem mobile can not light logo and may it shows blank in it.in iphone 4-4s condition you can only see light signe in mobile but it will not
First step is open mobile and check iphone 4-4s lcd connecter points on borad if there is a good value in it then change LCD with new one.Problem will be solve.
if only connecter points do not show value then chek all lcd connecter track and parts that are used in light function in iphone 4s parts and track are given in bellow diagram
check all these parts and components and if necesory resold or change them.this will help you in iphone 4-4s blank Solution Jumper Problem