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[SOLVED] 820-2850 backlight

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  • [SOLVED] 820-2850 backlight

    had liquid damage, fixed everything else up to this point

    replaced C9560, C7241, C7282, C7281, L9000, C9010, F9800,C9802

    R9808 and R9809 but the last two are reading at ~100k in circuit instead of their proper values

    PPBUS_S0_LCDBKLT_FUSED 12.6V ok

    PBUS_S0_LCDBKLT_EN_DIV reading 6.31V
    at first it starts at proper 4.21V and then jumps up to the 6.31V

    Is it Q9806 or am I looking in the wrong place, the LVDS connector is questionable but seems to work.
    Last edited by larossmann; 03-07-2017, 01:18 PM.

  • #2
    Voltages on pin 4, 8, 22, 23 of U9701?

    Voltage drop to ground on C9797?

    Comment


    • #3
      Just to clarify, is Q9806 not opening? Why are we looking at PPBUS_S0_LCDBKLT_EN_DIV? If it is not opening, what are LCD_BKLT_EN and BKLT_PLT_RST_L ?

      Comment


      • #4
        PBUS_S0_LCDBKLT_EN_L 3.42V
        BKLT_PLT_RST_L 3.3V
        LCD_BKLT_EN 3.3V

        U9701
        pin 4 negligible mv
        pin 8 3.3V
        pin 22 and 23 both 4.96V

        Comment


        • #5
          Bad Q9807....

          Comment


          • #6
            My vote is bad Q9807 as well. It's dual N channel meaning if voltage on gate is equal/higher than source it should let power flow meaning tat if LCD_BKLT_EN & BKLT_PLT_RST_L are 3.3v than PBUS_S0_LCDBKLT_EN_L should be ground. 3.42v is not ground!

            The voltage on pin 4 of U9701 comes from the voltage divider of R9731/R9715 whose power is sourced from PPBUS_S0_LCDBKLT_PW which comes from Q9806 which will not open so long as Q9807 is not opening and allowing the voltage divider of R9808 and R9809 to drop Q9706's gate voltage to ground. Q9706 is a P channel and will open when voltage on gate is sufficiently lower than the source.

            Replace Q9807!
            Last edited by larossmann; 03-07-2017, 12:00 PM.

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            • #7
              I guess it was a typo, replace Q9807!!

              Comment


              • #8
                No typo, good diagnosis! I agree with you.

                Comment


                • #9
                  Originally posted by larossmann View Post
                  My vote is bad Q9807 as well. It's dual N channel meaning if voltage on gate is equal/higher than source it should let power flow meaning tat if LCD_BKLT_EN & BKLT_PLT_RST_L are 3.3v than PBUS_S0_LCDBKLT_EN_L should be ground. 3.42v is not ground!

                  The voltage on pin 4 of U9701 comes from the voltage divider of R9731/R9715 whose power is sourced from PPBUS_S0_LCDBKLT_PW which comes from Q9706 which will not open so long as Q9707 is not opening and allowing the voltage divider of R9808 and R9809 to drop Q9706's gate voltage to ground. Q9706 is a P channel and will open when voltage on gate is sufficiently lower than the source.

                  Replace Q9707!

                  ..........

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                  • #10
                    I am but a cheap high copy of duke's intellect

                    Comment


                    • #11
                      That makes me the copy of the copy lol!!!!

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                      • #12
                        ok I did Q9807 and PBUS_S0_LCDBKLT_EN_DIV stabilized properly at 4.21
                        Q9806 was still reading nothing on left pins to inductor
                        did Q9806 (and a jumper to the fuse since that line seemed unreliable) and now it looks like it's all good

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