Lenovo ideapad 330-15AST - no backlight on battery

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  • xos
    New Member
    • May 2023
    • 3
    • Czech
    #1

    Lenovo ideapad 330-15AST - no backlight on battery

    Hi,i need some advice to fix this laptop. Laptop was spilled by water, cleaned and runs normally about 1 year, but now its no backlight on LCD, but when connenet AC adapter runs well with backlight. Battery was replaced with new one but problem presist.

    +LEDVDD ON ac 19,4V
    +LEDVDD ON BATTERY 7,5V

    [MOD EDIT]
    Link to schematic - https://www.badcaps.net/forum/showthread.php?t=116545

    Thanks for help.
    Last edited by SMDFlea; 11-02-2023, 04:48 AM.
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 13898
      • Canada
      #2
      Re: Lenovo ideapad 330-15AST - no backlight on battery

      With only the battery - can you see the graphics on the LCD? Use a phone in torch mode to shine on the front face of the LCD to confirm. Otherwise, the LCD is off.

      Sounds like the issue may be with the LCD screen and its internal LED power supply.

      What is the voltage to ground of INVT_PWM signal on the LCD connector with the power adapter? With only the battery ?

        Comment

        • xos
          New Member
          • May 2023
          • 3
          • Czech
          #3
          Re: Lenovo ideapad 330-15AST - no backlight on battery

          Forgot mention that picture is present but only backlight is not on battery. And voltage on INVT_PWM is 3,10V on battery and same for AC adapter.

            Comment

            • mon2
              Badcaps Legend
              • Dec 2019
              • 13898
              • Canada
              #4
              Re: Lenovo ideapad 330-15AST - no backlight on battery

              Good. Remove all power. Meter in lowest resistance scale. What is the resistace across R22 on the logic board? This should be ideally ~0 ohms.

              Comment: Based on your shared measurements, to me it appears the issue is inside the LEDVDD rail of the display. I can see a 'hack' solution which is to remove R22 and insert instead a voltage boost board (should be very low cost) to accept the battery voltage of ~8 volts and boost it to ~19 volts to feed on the other side of the removed R22 component.

              The LED backlight current is usually very low. It is only an idea but since the adapter ~19v feed on LEDVDD works but the ~8 volt from battery does not, yet the display is not defective for the graphics - only the backlight circuit is of concern.

                Comment

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