thread top ad

Collapse

Announcement

Collapse
No announcement yet.

[SOLVED]820-2850 no backlight

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • [SOLVED]820-2850 no backlight

    This laptop was working ok, video and backlight.
    I opened this laptop to replace a cap and now when I tested, has video (can see blinking folder) but no backlight. I checked led driver LP8545 and has a hole. I replaced it with new one and check for short before and after the diode. No short. After replacment I do have 25 at PPVOUT_S0_LCDBKLT. I check this on diode and on lvds connector, but still no backlight, only blinking folder.
    I tested with another working screen and lcd cable and no backlight. What is next to check?

  • #2
    PWM signal to LP8545?

    Comment


    • #3
      PWM pin2 - 2.16V

      Comment


      • #4
        That is all fine and 25V would also mean there should be backlight. Check on diode mode if pins 38-40 actually have continuity to the other end of an LCD cable.

        Comment


        • #5
          I dont have opened screen to check but I tested with another screen and LCD cable assembled and no backlight. Replace LVDS connector is worth it?

          Comment


          • #6
            I just took a lcd cable I have for 2012 model and put it on this board and I tested 3 backlight pins and all them goes to the other end of LCD cable. In the other end I found 2 pines. Pin2 and pin3.

            Comment


            • #7
              BKLT_EN high? Do a PRAM reset and see if PWM signal goes higher than 2.16V

              Comment


              • #8
                I did pram and smc reset. Still no backlight, but PWM goes higher yes.

                PWM - 2.45V
                BKLT_EN - 3.1V
                After D9701 - 24.82V

                Comment


                • #9
                  Diode mode on all LED return lines at the LCD connector?

                  Comment


                  • #10
                    With lcd and screen conected pins

                    31-36 0.671/0L

                    Red to ground - 0.671
                    Black to ground - 0L

                    Comment


                    • #11
                      Duke, something more to try?

                      Comment


                      • #12
                        Remove R9704 and connect pin 2 of R9704 directly to 3V, like to C9711.

                        Comment


                        • #13
                          I did what you told me. Now in pin2 of LP8545 I have 3.28V, and after D9701 I still have the same 24.82V. Still no backlight. Obviously it is not PWM problem. What more can could be?

                          Comment


                          • #14
                            I took again another macbook 2010 and put there the motherboard and I affirm the same. I have video, I see the folder blinking but missing backlight with another screen and LCD cable.
                            It is board issue, but what more could be?

                            Comment


                            • #15
                              I have no idea. Compare the 25V to another 15" machine. It could be bad solder or dead LP8545 again. Check resistors around the LP8545 and check if no components were moved/blown off while replacing LP8545.

                              Comment

                              thread bottom ad

                              Collapse
                              Working...
                              X