the external interface power priority

When the two-way power supply at the same time, the external interface power priority, while the two-way power switch is controlled by an electronic switch, the main current of the machine to achieve protective effects, and prevent short circuits or leakage on the phone's internal IC damage, however, if the electronic switch is damaged, the power module, there may not be caused by the supply voltage of the battery cell phone does not boot,  Maintenance can also be powered through different ways to provide power to distinguish electronic switch fault coverage and determine whether it is normal.

13mhz clock circuit start-up, you should make sure 13mhz clock signal through the resistors, capacitors and input to the amplifier circuit pin cpu, cpu clock input pin, the line should be checked if there is no resistance, capacitance, whether Weld or without amplification circuit power supply and damage. Cpu reset signal is also one of the working conditions, the symbol is resrt shorthand rst, Nokia phones using the purx representation. Reset generally leads directly from the power ic cpu or use a dedicated reset small integrated circuits, reset the boot moments exist.

Fifth, the logic circuit does not boot normally caused by the logic circuit for each memory key overhaul cpu chip select signals and license ce signal oe, these signals are very important, but the key is to find these signals must be. As more and more cell phone circuit uses IC bga package, to find these signals and their measurement points. Chip select signal are some vertical jump pulse signal. the electronic switching power supply for such a mobile phone, can be used as either an external power supply interface, the battery can be Trigger films, to be powered with an external power supply.
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