Let us turn to the process to power on:.
Press the Power button → power on instructions are sent to the power supply IC control module → Power IC receive the signal →Power IC begin to work → CPU; 13MHz master clock receive the electronics → CPU power on reset and complete the initial program → CPU send poweron signals to the power supply IC → power on IC stable output power for each unit → mobile phone is powered on and network begin to search and then enter the registration stage.According to the process of power on, we can analyze the relevant parts of the following need to be inspected and processing:
. As the boot keys is used very frequently, is this button being exposed?
. Is the Power Supply IC module cold solder joint or is  burned-out? Coz the IC operating current is large,so the  probability of failure for it is high.
. Whether is there signal sent to the CPU by Power Supply IC?
. Power Supply IC load a certain way of leakage or short circuit, causing the  current of power on  big, and thus the mobile is powered off in order to protect it. Common failure point is PA or the PA of the MOS switch is burned.
. CPU corresponding pin cold solder joint? This is a common point of failure.
. To work the three basic conditions for CPU are needed: (a) 3V operating voltage; (b) 13MHz clock; (c) reset circuit.
. Whether is there the signal of poweron output to the power supply IC on CPU?
. Does the initialization software error? Try to re-write the software.
(Note:When check this  failure, we can use man-made element separation, that is, using man-made cross-connection (can use a short thin enameled wire) on the power supply IC's poweron to  plus a voltage, if the power supply IC are able to output the normal voltage, then the failure is usually in the CPU control section or software, whereas the point of failure in the power IC or part of its payload. When inspect, can check it according to the signal ,the method is depending on the specific circumstances and the mobilephone)