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Huawei P8 Lite L-21 - The phone does not turn on.

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  • Level 12  
    Hello, I have a problem with the Huawei P8 Lite ALE-L21 phone that does not turn on. In general, the phone only worked with a larger backlight, the LCD began to flash and the phone took over 1A. The U2001 system was warming up so I decided
    replace it, unfortunately I did not notice that during the exchange I shorted the coil with the ground. Now the phone does not turn on, when connected to the computer, nothing works. I noticed that on C302 I have only 1V and it should be
    2.5V and after turning on the power on L300, L301, L302, L304 coils, no Buck voltage. Could U301 be replaced? Huawei P8 Lite L-21 - The phone does not turn on. Huawei P8 Lite L-21 - The phone does not turn on. Huawei P8 Lite L-21 - The phone does not turn on. Huawei P8 Lite L-21 - The phone does not turn on.
  • Level 16  
    VPH voltage is? Connect only the usb plate (without batteries) and then measure the voltage on the buck. It's best to use an oscilloscope to see if you have a short circuit on any of the lines. Also check that the oscillator (X402) is working.
  • Level 12  
    VPH is. I changed the oscillator to the second phone still does not turn on. There is no voltage under USB.
  • Level 16  
    How did you check these voltages? Meter or oscilloscope? On the oscilloscope, you can see if the U301 is trying to start (instantaneous peak voltage at the outputs).
    I asked you to check if the oscillator is working to make sure that the U301 is working.
    Shorting the L2002 coil to ground may not whip u301.
    When I think so now, most likely during the replacement of U2001 you were warming up too much and the balls came out from under U301, or there was a short circuit under it. But without the right measurements, it's just taking.
  • Level 12  
    By meter, I do not have an oscilloscope. In 2001 it was glued and probably your theory of damaged balls is true. Although I did it carefully.

    Added after 4 [hours] 24 [minutes]:

    The maximum heating temperature I used was 340 degrees. When the phone connected to the power supply does not show a short circuit.
  • Level 16  
    The power supply short circuit will only show you if it is on VBAT or VPH. However, the short circuit after U301 will be characterized by the fact that the voltage at the outputs of this system will appear for a short period of time (this time depends on which line is the short circuit, because all outputs start in turn, not all at once). PMU, after detecting a short circuit, resets and tries to start again.

    In this case, the heating temperature has the least impact. The more important is the heating time, because the longer you heat, the more the temperature spreads over the plate, which, if other glued elements are nearby, causes the balls to push the balls out from under the system.

    I set 450 degrees to change this element, but I play very briefly. I have not yet damaged it in this way u301.

    If you decide to replace the U301 (I'm guessing you probably don't have reballing equipment), here you have to be very careful, because when you replace it you can kill the processor.
  • Level 12  
    Thanks for clarifying my problem.
    The disc is intended for parts. Rather I will not replace the U301, I do not have such equipment. I have one more disc that resets all the time. The plate after flooding, of course cleaned. There is no short circuit on VBAT and VPH. So the reset can also be associated with a short circuit after the U301 system? Using a meter, it will detect which PMU line has a short circuit?
  • Level 16  
    Yes you will. Of course, if it is not a reduced resistance, only a short circuit. Set the meter to check circuit continuity and check each output of U301 in turn. It will take you a bit, because you have to check all BUCKs and LDOs, and there are some.
  • Level 12  
    Is it possible to observe a temporary peak of voltage at the outputs with such a toy as dso138 ?.
  • Level 12  
    I noticed that on L302 I only have a moment of tension then disappears. Buck1, buck3 and buck4 are normal. After connecting the power supply, the current consumption is 0.05A and disappears after a few seconds. On the L203 coil I have 3.66Va should be 3.8-4.2V. I have a damaged U301 or U201? Will someone suggest?