If keypad call menu end keys are not working in Samsung GT-S5260 It can be cause or key damages or water damages in the mobile phone.If smartphone keys are not working you can do these steps that are given in this post and diagram bellow.
Samsung S5260 Front Three Buttons Not Working Solution
Samsung S5260 Menu Key Jumper
Samsung S5260 Calling Button Not Working Ways Solution
Samsung S5260 Menu Key Button Jumper Ways Solution
After dis assemble of Samsung S5260 look at mother board and If you found some rust carbon or water damages then it can also be cause of Samsung S5260 keys problem to solve and fix keys problem clean all the rust and carbon with electronics cleaner and apply hot air to make it dry.
In above diagram you can see some different color lines. These lines are tracks and paths of keys button switch that are used for keypad lock and volume of keys button switch.
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