Strange VCCSA - Lenovo G470 - LA-6751P

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  • caspian
    Badcaps Legend
    • Oct 2015
    • 1589
    • Laptop

    #1

    Strange VCCSA - Lenovo G470 - LA-6751P

    Dear Members,

    When the laptop is cold, if I turn it on, it boots fine and gives display.
    Then after 10 to 60 seconds (randomly), the VCCSA voltage gets 0v and the laptop shows white screen. then after 3 seconds, the laptop turns off.
    Then if I turn the laptop on, VCCSA is zero and the laptop has black screen. then I have to wait about 15-30 minutes to get picture on this laptop.

    VCCSA is generated by RT8209B (PU601). Here is the link to the schematics. PU601 is on Page 50:
    https://www.badcaps.net/forum/attach...7&d=1591338538

    when it gives display, the pins are as follows:
    Pin 1 (En): 3.3v
    Pin 2 (Ton): 2v
    Pin 3 (Vout):
    Pin 4 (VDD): 5v
    Pin 5 (FB):
    Pin 6 (PGOOD): 3.3v
    Pin 7 (GND): 0v
    Pin 8 (PGND): 0v
    Pin 9 (LGATE): ?
    Pin 10 (VDDP): 5v
    Pin 11 (CS): 0v
    Pin 12 (PHASE): ?
    Pin 13 (UGATE): ?
    Pin 14 (BOOT): 5.8v
    VCCSA : 0.9v

    when it does not give display, the pins are as follows:
    Pin 1 (En): 3.3v
    Pin 2 (Ton): 0.02v
    Pin 3 (Vout): 0v
    Pin 4 (VDD): 5v
    Pin 5 (FB): 0v
    Pin 6 (PGOOD): 0v
    Pin 7 (GND): 0v
    Pin 8 (PGND): 0v
    Pin 9 (LGATE): ?
    Pin 10 (VDDP): 5v
    Pin 11 (CS): 0v
    Pin 12 (PHASE): ?
    Pin 13 (UGATE): ?
    Pin 14 (BOOT): 4.6v
    VCCSA : 0v

    Neither PU601 nor its surrounding Mosfets/resistors/capacitors get warm. the Mosfets are not shorted.
    resistance on VCCSA is about 40 Ohms.

    Now I do not know whether PU601 needs to be replaced or one of its surrounding Mosfets/resistors/capacitors or the CPU is defective?
    Please give your opinion.
    I have doubt that the cpu may force PU601 stop its output voltage.

    Thanks
  • qayyum786
    Badcaps Legend
    • Aug 2018
    • 1933
    • INDIA

    #2
    Re: Strange VCCSA - Lenovo G470 - LA-6751P

    CUT THE TRACK BETWEEN "PL601" AND PC605 CAPACITOR
    THAN CHECK FOR VOLTAGE on COIL PL601

    Comment

    • piernov
      Super Moderator
      • Jan 2016
      • 4435
      • France

      #3
      Re: Strange VCCSA - Lenovo G470 - LA-6751P

      CPU is not soldered so most reasonable would be to try another CPU first.
      Then try to reflow PU601 solder joints.
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

      Comment

      • caspian
        Badcaps Legend
        • Oct 2015
        • 1589
        • Laptop

        #4
        Re: Strange VCCSA - Lenovo G470 - LA-6751P

        thanks
        I replaced PU601. Now when I turn the laptop on, VCCSA is present for a few seconds, then VCCSA gets 0 volts. Then, white screen appears.
        When CPU is connected, resistance on VCCSA is about 40 Ohms.
        When CPU is not connected, resistance on VCCSA is about 20 KOhms.
        I do not have another CPU to test.

        Do you think the CPU is faulty or the VCCSA's Mosfets needs replacement?

        Comment

        • caspian
          Badcaps Legend
          • Oct 2015
          • 1589
          • Laptop

          #5
          Re: Strange VCCSA - Lenovo G470 - LA-6751P

          Could someone please confirm what resistance exists on VCCSA coil when a second-generation Intel sandy-bridge CPU is installed on the mainboard?

          is 40 Ohms too low for VCCSA?
          Last edited by caspian; 06-07-2020, 11:36 AM.

          Comment

          • caspian
            Badcaps Legend
            • Oct 2015
            • 1589
            • Laptop

            #6
            Re: Strange VCCSA - Lenovo G470 - LA-6751P

            I replaced the CPU. I replaced PU601 and its Mosfets. But nothing changed. VCCSA is still acting the same.
            The laptop gives display only when it remains off for more than 30 minutes.
            If I turn it on for the first time, it gives display but VCCSA gets 0 volt after 30-50 seconds.
            Then if I turn the laptop on, VCCSA will not be present although PU601's Enable pin is 3.3v. Then, I have to wait more than 30 minutes to have display.
            What do you think is defective?
            Last edited by caspian; 06-13-2020, 10:08 PM.

            Comment

            • mcplslg123
              Badcaps Legend
              • Jun 2015
              • 7262
              • india

              #7
              Re: Strange VCCSA - Lenovo G470 - LA-6751P

              When display goes off, +1.05V PCH Pwr remains ok??

              Comment

              • caspian
                Badcaps Legend
                • Oct 2015
                • 1589
                • Laptop

                #8
                Re: Strange VCCSA - Lenovo G470 - LA-6751P

                yes, the +1.05V rail remains present and stable. However, the +1.05V rail is measured as many as 1.07 volts.
                and my multimeter is precise in measering voltage.

                Comment

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