ASUS U303L notebook repeated auto power off restart repair

Machine model: ASUS U303

Main board number: UX303LN

Malfunction: notebook repeatedly reboots auto power off.

Maintenance process:

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

ASUS U303L notebook repeated auto power off restart repair Figure 1.
Remove the motherboard, measure the power on roughly with an oscilloscope, and open the dot diagram to find SUSB# fixed channel 2. And find PM_PWROK.

ASUS U303L notebook repeated auto power off restart repair Figure 2.

ASUS U303L notebook repeated auto power off restart repair Figure 3.
The waveform measurement found that SUSB# dropped first. RSMRST and EC_RST were measured again, and they never dropped.

ASUS U303L notebook repeated auto power off restart repair Figure 4.
Measure the waveform of CORE_PWRGD conveniently.

ASUS U303L notebook repeated auto power off restart repair figure 5.

ASUS U303L notebook repeated auto power off restart repair figure 6.
Measure PU8000 VCCIN_EN again, and obviously turn it on and turn it off first. Explain that there is VCC abnormal or unstable before CPU VCC.

ASUS U303L notebook repeated auto power off restart repair Figure 7.
When PQ9101 is found, it is an Switch pipe.

ASUS U303L notebook repeated auto power off restart repair Figure 8.

ASUS U303L notebook repeated auto power off restart repair Figure 9.
Here’s the problem. Look at the waveform.

ASUS U303L notebook repeated auto power off restart repair figure 10.
Measure the control electrode of PQ9101 again, and VCC doesn’t work properly. It should be 12V normally. Directly disassemble the resistor PR9104, which is no longer auto power off, but 12V sounds normal.

ASUS U303L notebook repeated auto power off restart repair figure 11.

ASUS U303L notebook repeated auto power off restart repair figure 12.
That’s the problem with PQ9101. Unplug the power, directly connect 4 and 5 pin together, and the boot is normal.