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There are many causes for Samsung won't turn on issue. As for Samsung not turning on accompanied with 50mA-80mA boot current, the first thing we usually do is to check the power supply voltage. If nothing goes wrong, the fault is most likely related to CPU. If there is abnormal voltage measured, then check the corresponding faulty position on the board.

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  1. Press power button. The phone won’t turn on.
    • Press power button. The phone won’t turn on.

    • Take apart the phone. Take out the SIM card tray and logic board.

  2. First, we need to confirm whether the boot current is normal.
    • First, we need to confirm whether the boot current is normal.

    • For better measurement, apply solder to the battery connector. And solder a length of red supply wire.

    • Trigger with tweezers to power on the phone. Current reading on the ammeter is 50mA.

    • For 50mA boot current of the phone, the fault is usually related to CPU and main power supply voltage.

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  4. Next, let’s measure the power supply voltage.
    • Next, let’s measure the power supply voltage.

    • Disconnect the power supply. Remove the shield plate. Trigger with tweezers to power on the phone.

    • Measure L7012, L7011, C7067, C7044, C6040, L7015 and L7004 one by one. The measured voltage of C7067 is lower than normal value.

    • We can confirm now that the fault component is PMIC U7003. We need to replace with a new PMIC.

  5. First, remove shield plate on PMIC with Cutting Nipper. Then heat up with Hot Air Gun. Detach PMIC from the board.
    • First, remove shield plate on PMIC with Cutting Nipper. Then heat up with Hot Air Gun. Detach PMIC from the board.

    • Apply some Paste Flux to the bonding pad. Clean the bonding pad carefully.

    • Apply some Paste Flux to the bonding pad. Get a new PMIC in position. Solder with Hot Air Gun.

    • Once done, wait for the logic board to cool for 5 minutes. Clean with PCB Cleaner afterwards.

  6. Now we can assemble the phone and test.
    • Now we can assemble the phone and test.

    • Press power button to power on. The phone turns on normally.

Phryne

Membro da: 17/11/2019

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