DELL 3421 Does Not Power On

 

Laptop Model: DELL 3421

 

Board Number: 12204-1

 

Fault: The Notebook Does Not Trigger, Does Not Power On, And Is In Standby Mode At 0.01

　

Maintenance process:

 

There is no short circuit in the whole board. Only the resistance of the CPU and the graphics card to ground is relatively low (the resistance of the third-generation onboard CPU to ground is generally 3-5 ohms), the voltage is 3V5V, the EC power supply is reset normally, and AC_IN# is 0V ( EC 73 feet are normal).

    LID3.3 is normal, but the voltages of RSMRST# and PWRBTN are constantly jumping, and the power supply indicator light in the lower left corner is also flashing.

Find RSMRST# and PWRBTN next to the EC and cut them off directly.

    The voltage on the EC side kept jumping from 0V to 3V when measured. Replace the EC directly. After replacement, the fault remained the same. I reviewed the EC working conditions again and found that except for the two voltages RSMRST# and PWRBTN that kept jumping, everything else was normal.

　　

    I had to go to the oscilloscope to check whether each voltage output was stable. The common terminal, 3V5V, and the 3V5V linear voltage. The oscilloscope directly adjusted the automatic gear and caught 19V. The linear 3V5V was normal, but when it caught 3V5V, it was repeated and the voltage would drop instantly. Go up again.

    Then grab PWR_3D3V_EN2 and PWR_5V_EN1, the voltage will be pulled down and up again repeatedly.

    It is traced that the source of PWR_3D3V_EN2 and PWR_5V_EN1 is EC and connected to the PURE_HW_SHUTDOWN# signal. PURE_HW_SHUTDOWN# controls ECECRST#.

　　

    When grabbing PURE_HW_SHUTDOWN# and ECECRST#, the voltage will be pulled down and up again repeatedly. It is normal to directly remove Q2701 and grab ECRST#.

　

　But PURE_HW_SHUTDOWN# will still be pulled down repeatedly, because PURE_HW_SHUTDOWN# went to several places, and after looking for it for a long time, I only found D3601.

    I couldn't find anything else, so I took off the D3601 directly. After taking off the D3601, the board triggered the display normally. I installed it directly and tested it repeatedly for half a day, but it was normal. I was too lazy to trace the source of the PURE_HW_SHUTDOWN# signal.

Summarize:

　　The fault point is that PURE_HW_SHUTDOWN# is unstable, causing ECRST to reset continuously, causing the computer to not boot.

Happy Repairing !!