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no booting deep sea machine maintenance ghost

After the machine was disassembled, the BIOS was immediately flashed, which was useless. It was found that the EC also had BIOS, and the failure was still the same. Check the en of U1 to open VCC.When measuring 3.3V to ground, the resistance is zero. It is 3.3V Short circuit Current protection.

Lenovo y400 notebook boot no response maintenance

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Quickly dismantle the machine, first dry the standby 3 / 5V in the figure below, open the control MOSFET and force it on.Measure the standby 3 / 5V VCC OK, then test the standby and reset of EC, and then check the EC reset is low, and hit 3V linear waveform.The fault caused by the 3V line current of change has been eliminated, and then the 3 / 5V is also current of change. First, disconnect the 3 / 5V isolation point, and then turn off the 3 / 5V. Finally, replace the two pairs of MOSFET of 3 / 5V and power on booting up to remove the fault.