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820-4924 a1502 BKLT_EN, PP5V_S0 Missing

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  • 820-4924 a1502 BKLT_EN, PP5V_S0 Missing

    Whats up everyone, love you guys over at Rossman Repair Group, I have been working up the courage to start offering logic repairs to my customers (own a small repair shop) and your videos and knowledge have helped me work up to the point where I am actually doing some repairs, and have actually been successful in repairing a few, imagine that!

    Anyhow, it is great to be a part of this awesome community, and I can't wait to start helping people get their items fixed at a more affordable rate!

    So here is what I got going on! (Please bear with me as I still feel slightly stoopid with schematics and understanding how the board actually works, but I learn quick ;-)

    I've got a Macbook Pro 13" Retina 820-4924 a1502 board with no backlight.

    The LCD connector was partially melted off so I have already replaced that, hoping that would be it, but of course not.

    From what I can tell there is NO PP5V_S0, which I believe based on the schematics that is what goes into the LED Driver and powers the Backlight Enable?

    The Q7700 is not enabling if it has 12v on the LCDBKLT_EN pin is that correct?
    I am getting the 12v at the PPVIN_S0SW_LCDBKLT but it is not making it to r7742 which is the BKLT_EN Resistor. Hope I am doing ok on this.

    I am not sure what to do, and the only other question I have is this, does this board need to be powered on with the keyboard or do I need to power it on with power pads in order for the backlight voltage to appear?? Because if so, I am not doing that, and only have the board plugged in alone without anything else while testing.

    I have put the board back in the unit and it still displays an image, but still no backlight!

    I really appreciate what everyone does here and I spent about 5 hours yesterday trying to figure this out on my own, with videos/brdview software. I just think I need a little more teaching before I can repair these in a respectable time limit, because I just cant spend this much time on a board haha..

    Thanks for reading, and I eagerly await the knowledge!

    David Rainer
    Computer Booter

  • #2
    "there is NO PP5V_S0
    I have put the board back in the unit and it still displays an image"
    How do you get image then???
    Where did you check that?

    Post U8300 voltages here...


    • #3
      Just was watching Louis' video on his repair, and he found a short to ground off the bklt_en resistors, well I found one too at C8359 which is the IC2_BKLT_SCL line, I just removed it and the short is still there, so I guess that means I need to check the rest of those Capacitors in the line?? I am working on that, and I will also get the U8300 voltages right now.

      "there is no pp5v_s0" I guess that means I am wrong about that statement, sorry about that.. still learning. but I know 5v is missing all around the backlit driver and bklt_en resistors... unless the screen needs to be plugged in to get those?? Will report back soon, thanks!


      • #4
        I was thinking you reffer to R8320 voltage.
        5V must pass through U8300 before goes there.
        Should be there few seconds at least, when you here chime; even without LCD.

        Remove R7750 and see where the short remains.


        • #5
          Thanks for the help, I actually found that it was shorted at R7750 and then read your comment, :-) I removed it and the short is gone... So I'll need to replace that resistor and the capacitor I removed unecessarily... Ill need to find the part from a donor board.... I need to replace these for the BKLT enable to reach the screen and test it right? I hope this is all hahaaaa but it WAS fun!


          • #6
            A resistor can't short anything to ground.
            I asked you where the short remains...
            It is on the side of U7700?
            I think yes, pin15 of it.
            So you must change the chip...


            • #7
              So, the Capacitor I removed was shorted to ground C8359 I2C_BKLT_ICL, when I removed that, the pads were both shorted to ground. So you recommend I remove R7750 which I did, that removed the short, or are you saying that its not a short, but maybe I misunderstand... I replaced R7750 and I still have no backlight...

              Ok I will try a new chip, ill have to order one unless this 820-3437 board has the same IC

              I really appreciate the time you are taking to help me, so thank you again!


              • #8
                A short on pin15/U7700 will appear on C8359 through R7750 too.
                If remove that resistor, short will stay on U7700 only; not anymore visible from C8359.
                Is that I told you to check...


                • #9
                  Thank you for bearing with me, (this newb) I now have a bklt_en voltage after replacing the r7750 but no backlight.. I have ordered x2 LED Driver chips from your site, and I hope after replacing it things will be different haha, is there anything else I should check before receiving the new chip?? I do believe that the cap C8359 destroyed the LED driver as a similar cap in Louis' video did as well.

                  I am still getting 12v on both pin 3/4 on U5450 which I understand means it is not switching over either?? Sorry I dont quite understand, but from what Louis said in the video, this should be 12v on pin 4, and about 5-6v on pin 3 in order for the backlight to operate, is that correct?

                  I will replace the LED driver and test again. I love learning this and have learned a lot by watching the videos and am honestly amazed at the support and response you are giving to people... I appreciate it!

                  Last edited by ComputerBooter; 08-30-2018, 05:13 AM.


                  • #10
                    I will check the resistance from pin 15 to ground at the LED Driver today, I have already ordered more LED driver IC's from your site, but ill continue to try and learn and understand how the logic is working for my own, and my customers benefit! The 820-4924 backlight repair the Louis' did is practically the same as this one, and near the end of the video he finds out that the cap for BKLT_SDA had blown the donor LED Driver that he had installed, so after removing that cap, he replaces the LED Driver for the second time, and then he gets backlight. So I will check the resistance to ground at pin 15 of the LED IC, which I am assuming will be almost 0 and then once I get the LED driver I will replace it! Fun fun fun!


                    • #11
                      Ok haha that did not go well, after I replaced the LED Driver, since im a n00b, it ended up burning up the LCD connector for some reason, and now it would need a new screen since replacing that connector is practically impossible, unfortunately I will not be repairing this MacBook! I'll stay on the 29$ forum fee for a while though even though I rarely get logic level repairs, because Rossman deserves my sub, thanks for all you do!


                      • #12
                        The LCD cable can easily be replaced on retina LCDs!


                        • #13
                          Originally posted by dukefawks View Post
                          The LCD cable can easily be replaced on retina LCDs!
                          oh yeah? I never knew as the older models it was a PAIN, ill have to remember this for next time as I already gave the customer her computer back. She is going through her insurance to get it replaced but might still have it repaired, depending on insurance. Thanks, and ill have another board that has missing Wifi and loud fans to repair here soon. Second attempt at repairing it. Ill start a new post


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