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If keypad lock key or volume keys are not working in Nokia C5-03 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.nokia c1-01 light problem solution jumpers Tested 100%

After dis assemble of Nokia C5-03 look at mother board and If you found some rust carbon or water damages then it can also be cause of Nokia C5-03 keys problem to solve and fix keys problem in Nokia C5-03 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.
Check all these tracks with meter and apply jumpers. If these key switches are not working then you can replace volume and keypad lock buttons.
for more detail and new tips and tricks about cellphone service problem keep visiting this page we will update cellphone service diagrams timely with new cellphone diagrams.some related post are also given bellow you can read them also for more information about cellphone.

Heres a solution for Nokia N97 backlight LED on the QWERTY keys not working or failed to light up.
This solution can be used if the keypad membrane flex is not damaged but the LED backlight still wont light up.


The solution above shows the qwerty keypad backlight LED circuit, it is composed of LED driver IC and filtering Resistors. These Resistors has a 0 ohms resistance value, you may check first these resistors before troubleshooting  further.
The LED driver needs the Battery Voltage which is 3.7 volts that came across with red color highlighted component Resistor, check that voltage and continuity to the battery B+ terminal.
If all the Resistors were okay, you may then proceed to check or replace the LED Driver IC.