ASUS U303L notebook repeatedly loses power and restarts repair

Measure PU8000 VCCIN_EN, and drop it first when it is obviously turned on. It shows that there is abnormal or unstable voltage before CPU power supply. Directly disassemble the resistor PR9104, the power has not been cut off, and 12V sounds normal.

Machine model: ASUS ASUS U303L notebook

Main board number: UX303LN

Fault symptom: The notebook is restarted after repeated power failure.

Maintenance process:

An ASUS ASUS U303L notebook, the fault is that when plugged in, the current keeps dropping by 0.18A, 0.12A and 0.08a.. It can power on automatically, but the current is different every time.

ASUS ASUS U303L Notebook Repeatedly Power Down and Restart Maintenance Figure 1

Remove the motherboard, roughly measure it with an oscilloscope, and open the dot diagram to find SUSB# fixed channel 2. Then find PM_PWROK.

ASUS ASUS U303L Notebook Repeatedly Power Down and Restart Maintenance Figure 2

ASUS ASUS U303L Notebook Repeatedly Power Down and Restart Maintenance Figure 3

The waveform measurement found that SUSB# dropped first. RSMRST and EC_RST were measured again, and these have not been dropped.

Measure the waveform of CORE_PWRGD at will.

Measure PU8000 VCCIN_EN again, and drop it first when it is obviously turned on. It shows that there is abnormal or unstable voltage before CPU power supply.

When PQ9101 is found, it is a switch tube.

Maintenance diagram of ASUS ASUS U303L notebook repeatedly powered off and restarted.

The problem is found. Look at the waveform.

Measure the PQ9101 control pole again, and the voltage is not normal, which should be 12V. Directly disassemble the resistor PR9104, the power has not been cut off, and 12V sounds normal.