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820-3332 no display/no backlight

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  • 820-3332 no display/no backlight

    no external (off hdmi)
    i tried good known lcd.
    Chime is present - both speakers are distorted!



  • #2
    Resoldered U8900?

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    • #3
      yes now i have image but still no backlight. i got two of these boards on my desk with same issue - hopefully when i solve one it will also fix the other. 12.6v on pin 1 on j9000.

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      • #4
        "12.6v on pin 1 on j9000."
        So you have LCD_BKLT_EN and of course BKLT_EN too.
        Do you get LVDS_BKL_PWM_RC?

        If not, do PRAM reset few times.
        If still no result, remove R9704 and run a wire from LVDS_BKL_PWM_RC to BKLT_EN.
        If works, do PRAM reset again.
        Resolder all components (remove the previous wire),test and comment...

        Consider to remove EFI password, if is the case.

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        • #5
          3.3v on lcd_bklt_en 3.1 on bklt_en
          lvds_bkl_pwm_rc is missing/very low ~100mv

          i remove r9704 and run jumper from bklt_en to lvd_bkl_pwm_rc still no back light.
          Last edited by MegaObi; 3 weeks ago.

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          • #6
            Check all traces and components around U9701.
            Pay atention to R9708/09 and all return resistors.
            Try known good LCD assembly.
            Change U9701.

            Do all these tests keeping 3V at LVDS_BKL_PWM_RC.

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            • #7
              i changed u9701 still same i get 2.49v on lvds_bkl_pwm_rc
              Last edited by MegaObi; 3 weeks ago.

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              • #8
                hey solved was bad u9701

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