Lenovo E420 laptop unable to turn on

Machine model: Lenovo E420

Fault phenomenon: laptop Won’t Turn On

Maintenance process: remove the battery and power on automatically to 0.39a. The common failing of this machine is not standby no power on, and the automatic starting current is 0.3A. It is estimated that the battery will start automatically when the battery is not powered on. The quotation Customer agrees to start dismantling.

This 0.39a should be missing VCC, so it is customary to start from the simplest repair. First test CPU VCC to 0, and check 9 pin VCC 0 of pu4201.

Lenovo E420 laptop unable to turn on Figure 1.

D85V_Pwrgd signal is PGOOD signal sent by pu4801. It is not detected in EN.EN was 1.05 VTT_Pwrgd, and then the next level.

Lenovo E420 laptop unable to turn on Figure 2.

1.05VTT_Pwrgd signal is PGOOD signal sent by pu4501, and pu4501 is not EN.EN has two PWRs_1D05V_EN and runpwrok.

Lenovo E420 laptop unable to turn on Figure 3.

PWR_1D05V_EN is issued by u3609, but it is omitted as shown in the figure. Check runpwrok directly.The figure below shows that this signal is sent by pu4601 and pu4701 together, provided that the two signals are normally sent at the same time.

Lenovo E420 laptop unable to turn on Figure 4.

Lenovo E420 laptop unable to turn on Figure 5.

It is tested that pu4601 is open and output is 1.5V. It is found that pu4701 is not input. Check 1 pin as 3.2V. This is SHDN pin, and high VCC is off output.

This SHDN signal is converted by pq4701 field tube. Check that all three pin are 3.2V. The problem is it.Replace it directly, power on booting up directly, and the maintenance is finished.