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820-3332 no backlight

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  • 820-3332 no backlight

    Hey guys,

    very upset on this one. I checked fuse - got excited for the one time fuse was screwed so i thought oh wow - easy repair for once. changed fuse - next minute smoke coming out of lcd connector

    what do you think caused it - should i try again with new fuse and connector?

  • #2
    Bad contact inside LCD connector.
    Change connector and check video cable terminal too.
    Insert video cable and check for short/low value on corresponding pin (to ground).
    If OK, change the fuse and turn it on.


    • #3
      I changed lcd connector. pluged in screen checked for short to ground nothing changed fuse - and POF! AGAIN!
      is 260ohm too low?


      • #4
        "check for short/low value"
        I adviced you about low value too...

        Did you check the video cable terminal?
        Inspect it on both sides; better to change it.


        • #5
          im not confident to change cable on retina display.
          yes you advised correct.

          when you say check video cable you mean inspection? i have pin 1 now burnt i rebuilt with another pin and some uv curing.


          • #6
            You must check resistance to ground at pin 1 of J9000 once LCD cable is inserted.
            You must get practically the same value as when LCD is disconnected...


            • #7
              55.3k with no lcd connected.
              54.6k with lcd connected

              i havent replaced fuse yet but i pulled off board.

              scared to put back!


              • #8
                That looks good; is far away of 260 ohms before.
                Give it a try...


                • #9
                  good thing is no smoke this time! still no backlight


                  lcdbklt_en_l 11.72v
                  lcdbklt_en 0v
                  lcdbklt_en_div 11.9v

                  ppbus_s0_bklt_fused 12.4v
                  ppbus_sw_lcdbklt_pwr 0v
                  ppvout_s0_lcdbklt 56v

                  bklt_plt_rst_l 3.3v

                  pp5v_s0 5.1v
                  pp3v3_s0 3.3v

                  R9708 44k ???? 1%?
                  R9709 43.5k ???? 1%?
                  Last edited by MegaObi; 02-22-2019, 12:55 AM.


                  • #10
                    Why would you expect to get exact reading for onboard resistors???
                    Surrounding components alter the onboard test.

                    "still no backlight"
                    Do you get image at least?

                    "ppvout_s0_lcdbklt 56v"
                    How, if you don't get backlight enable?

                    56V output means no contact with LEDs strip from display; correct voltage 39V aprox.
                    Check for same voltage at pin 1/J9000.
                    Try known good (and compatible) LCD assembly.


                    • #11
                      hey informaticos. i dont expect exact reading but expected reading should be closes to tolerance.

                      yes i do have image

                      I am not sure how i had 56v before but now when i check pin 1 its 12.05v



                      • #12
                        "expected reading should be closes to tolerance"
                        Not true; reading depends by the other resistors, or ICs, in contact with measured resistor.
                        Closed loops through ground will create parallel resistors.
                        For high values, even positive power rail close the loop.

                        "Try known good (and compatible) LCD assembly."


                        • #13
                          ah ok great explanation.

                          i have already tried good lcd assembly. i forgot to put in my previous post.


                          • #14
                            "i check pin 1 its 12.05v"
                            This means you have LCD_BKLT_EN present; automatically BKLT_EN too.

                            Post again voltages for U9701 and Q9706/07.
                            Please provide accurate information, or any help is useless...


                            • #15
                              2 = 2.5v
                              3 = 0v
                              4= 3.1v
                              5 = 0v
                              6 = 0v
                              7 = 0v
                              8 = 3.3v
                              9 = 0v
                              10 = 3.3v
                              11 = 3.3v
                              12 = cycling
                              13 = .3v
                              14 = .3v
                              15 = 0v
                              16 = .3v
                              17 = cycling
                              18 = cycling
                              19 = 0v
                              20 = 0v
                              21 = 5.9v
                              22 = 5v
                              23 = cycling
                              24 = cycling

                              1/2/4/5/6 = 12.66v
                              3 = 4.12v

                              2 = 3.3v
                              3/4 = 0v
                              5 = 3.3v
                              6 = 0v
                              Last edited by MegaObi; 02-26-2019, 12:35 AM.


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