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Macbook Air 2015 no backlight

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    #21
    Re: Macbook Air 2015 no backlight

    Yes, the charge pump ic for the backlight could be defective. It took us 3 attempts to get it right for the soldering.

    Suggest to use sticky flux for the site along with kapton tape to protect any nearby parts you do not want to fly away.

    Use 400-500c hot air temps but low air pressure so parts for not fly away. Personally like 20-30 setting on our 860 on our unit from Best tools. Amazing hot air tool.

    When you think you have it right, power up without the lvds cable.

    Check the voltage out on the lvds connector. From memory, it should be 25v or higher if soldered correctly.

    Download the data sheet and review the schematic from Texas instruments. It is the same typical design used by Apple. This is very helpful to understand how this backlight device works.

    The good thing is that the part is cheap. Available from Arrow electronics.

    From memory, I recall the Apple schematic having a value for the voltage rail expected from this backlight controller if working correctly.

    What value do you see?

    As noted, our effort took 3 attempts to get it right but we did this without a microscope. Still on my wish list of purchases. Debating between desktop vs. mono style. The optics appear to be higher for desktop like used by Hussein at Northwest repair. About $1k usd for that setup.

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      #22
      Re: Macbook Air 2015 no backlight

      HI, friends!!!!
      I have reordered 10 new LP8550 IC, from Aliexpress, from a good reputation seller. My 5 first LP8550 have all being soldered without success... I solder with a Quick 861DW hot air station, with a low air blow (at 30) to avoid others components to fly away... At first, I had fixed my temperature at 500°C, as usual, then 420°C, then 280°C, considering that this LP8550 is small and contains a heat sensitive mosfet. I use a *10 magnifying microscope that I have bought 220 euros to my local electronics dealer and which gives a clear view of the chip alignement... Looking from the side, the microscope shows good contact of the bga balls under the IC with the board. Of course, I use tacky flux, from Chipquick, which usually works well.... To sum up, I do not understand this failure to repair this backlight......

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        #23
        Re: Macbook Air 2015 no backlight

        Don't buy from Aliexpress when you can get the chip from real distributors like Mouser…
        OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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          #24
          Re: Macbook Air 2015 no backlight

          Thanks for the advice, Piernov!!! I have a real admiration for your knowledge and all the valuable teachings you give us. Mouser has expensive shipping fees.... Would you advise another real distributor with cheaper shipping????

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            #25
            Re: Macbook Air 2015 no backlight

            On Texas Instruments datasheet of the LP8550, the peak solder temperature is mentionned to be 260C, when we solder at 500, 420, 400 or even 280C, we are far above the TI recommendations.........

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              #26
              Re: Macbook Air 2015 no backlight

              I have found ARROW, to be an official TI official distributor, with free shipping and I have been able to order 10 original LP8550 for 22 euros, comparated to 14,50 with Ali...

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                #27
                Re: Macbook Air 2015 no backlight

                What are the values for the attached sections of the backlight circuit?
                Attached Files

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                  #28
                  Re: Macbook Air 2015 no backlight

                  Hi!!!!
                  My PPVIN S0SW LCDBKLT FET line shows 8.5v....
                  I have not measured EDP BKLT EN neither BKLT PLT BST L, because if I get those 8.5V, the mosfets work correctly and it seems that I get no boost which should be LP8550 fault.....

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                    #29
                    Re: Macbook Air 2015 no backlight

                    What are the readings on the left side of the mosfet?

                    According to the schematic, should be about 12v.

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                      #30
                      Re: Macbook Air 2015 no backlight

                      Never trust voltage indications in schematics.
                      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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                        #31
                        Re: Macbook Air 2015 no backlight

                        This voltage is important.

                        What are voltages on Q7706,

                        Pin 3 ?

                        Pin 4 ?

                        The left side is PPBUS_G3H. If 8v6, that is too low.

                        Believe to have the same logic board at the office.

                        Will confirm the same asap.

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                          #32
                          Re: Macbook Air 2015 no backlight

                          PPBUS_G3H is always 8.4/8.6V on MacBook Air.
                          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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                            #33
                            Re: Macbook Air 2015 no backlight

                            Originally posted by vieuxchoub View Post
                            Could it be that my LP8550 ICs are defective???? I have changed it again this morning twice, at 280°C, with a very good look of the bga balls soldering under the microscope....
                            I rechecked the continuity of the SW and FB lines, with voltages of 8.3v of the FB line and 8.5v of the SW line.....
                            I do not understand what could be the problem...
                            It could be one of the DATA line problem if your Backlight voltage is 40V but if you have 8V then LP8550.
                            Last edited by MobileXT; 01-26-2021, 01:55 PM.

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                              #34
                              Re: Macbook Air 2015 no backlight

                              Dear friends!!
                              Thank you for all your answers....
                              I have measured the voltage at Q7706: pin3=2,82v and pin4= 8,55v but I had the surprise to measure 19,6v, for the first time after the backlight diode and at pin 3 and 4 of the LVDS connector. I have reassembled the Macbook: the result is better but not good. I get backlight but just on the right half of the screen and this backlight is slightly blincking....
                              What could it be??? Corroded LVDS connector???
                              Thanks a lot again for your help

                              Comment


                                #35
                                Re: Macbook Air 2015 no backlight

                                I have a post on Louis Rossmann forum of a guy having the half dim screen after soldering a backlight driver, like me... And like him, I had some problem in the led return lines: ISEN1, ISEN2 and ISEN3 were around 0.58v in diode mode measured at the resistors while ISEN4, ISEN5 and ISEN6 were OL...
                                I have tried to reflow my LP8550 and ISEN6 is at 0.58V now, while ISEN4 and 5 stays OL despite their balls under LP8550 viewed from the side under the microscope seem to attached..... Probably, my Chinese LP8550 is somehow defective. Maybe the backlight could work correctly with only ISEN 1, 2, 3 and 6 connected but it seems safer to change again this damned LP8550 with one genuine from ARROW that I am waiting for.....

                                Comment


                                  #36
                                  Re: Macbook Air 2015 no backlight

                                  @vieuxchoub, I think it is very good news on your discovery so far. Sounds like you will have this working soon.

                                  Do you purchase a lot of goods from Arrow? We do, and have a good shipping
                                  status with them and believe we can (drop)ship for free to Europe. We are in Canada. Let us know if you need any help on the sourcing of the same backlight driver IC. We order this from them all of the time. Great support for them to offer this level of service.

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