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Macbook Air 802-00165-A Good backlight fuse, bad wled?

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  • #16
    Well new screen and still no backlight. Ugh.... Anything else I could try?

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    • #17
      Right lets start over here.

      What is the voltage on pin 3,4 on LCD connector. LCD plugged in of course on not with the lid closed.

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      • brooke.j
        brooke.j commented
        Editing a comment
        Totally let's start over LOL! Ok so Pin 3,4 is 7.6V But as the board is left on it slowly drops. This must be the sleep Feature? Just FYI there is no HD installed. I have one if that makes it better?
        Last edited by brooke.j; 10-04-2016, 10:07 PM.

    • #18
      Which is crazy because I was getting 3.4v. Maybe I just murdered the WLED and didn't know it?

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      • #19
        Do you have an LCD plugged in while measuring? Also check SMC_LID

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        • brooke.j
          brooke.j commented
          Editing a comment
          I have the LCD Plugged in. SMC_LID is 3.4v, PIN 3,4 of LCD is 8.5v. So it looks like the lcd is getting too much?

      • #20
        Ok so I'l start over. Thank you again for all the help. This is with the LCD plugged in.

        Q7707 PIN 2 = 3.4v, PIN 5 = 3.4v
        LCD connector PIN 3,4 is 8.5v
        SMC_LID = 3.4v
        Q7706 PIN 3 = 2.8v (close enough right?) PIN 1,2,5,6 = 8.5v
        Last edited by brooke.j; 10-06-2016, 05:17 PM.

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        • #21
          That all looks fine. Now check BKL_EN and BKL_PWM.

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          • #22
            I've also cleaned the dam WLED driver too much and now if I wanted to replace it I don't know which way it goes. Can anyone help with that? Thx

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            • #23
              Oh I can figure it out from the data sheet (I hope)!!

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              • #24
                You have the board view for that. Please measure what I asked.

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                • brooke.j
                  brooke.j commented
                  Editing a comment
                  Ok I didn't see that post sorry I'll check those. Just a thought... there is only one LP8550 on mouser? Just want to make sure I got the right one. The numbers on top are different than on the original WLED.

              • #25
                BKL_EN = 2.8v BKL_PWM = 0.3v
                Measured at PIN 1 of R7715 and PIN 2 of R7704 respectively

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                • #26
                  BKL_PWM should be higher. Do a PRAM reset to be sure it is not that first. Then check resistance to GND on BKL_PWM.
                  If that all seems ok, remove R7704 and connect BKL_PWM to 3V somewhere, like C7711 and see if that brings it back.

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                  • brooke.j
                    brooke.j commented
                    Editing a comment
                    Thanks duke for hanging in there with me. I'll get on that right away. This forum and you super awesome!

                • #27
                  After PRAM Reset BKL_PWM went up to 1.4v. So I did what you said. Connected 3.4v from C7711 PIN 1 to R7704 PIN 2 (R7704 removed) That means I'm putting 3.4 V into the WLED driver. Did I read the schematic correctly? I figured I didn't want to double up on the voltage and I saw that R7704 was going into the WLED so I hope I got that logic right. Something curious happens with Q7707 PIN 5 EDP_BKLT_EN is 3.4v at start but then quickly goes to 0v and PIN 3,4 of LCD goes from 8.5v to 0v quickly too. This is with the LCD plugged in. Just to point something out that I know I'm going to get shit for. I bought a used "working" LCD to test because someone mentioned that the original might be bad. Would that make any difference if somehow this "working LCD I bought is bad. Also could I have just mangled the WLED driver replacement? I've Replaced it 3 times, desoldered the pads (all of them look nice) and have tried to get it perfect. Not heating it forever and seeing the chip move so that I know all balls are melted. But Maybe I'm just f'n it up or something.
                  Last edited by brooke.j; 10-09-2016, 08:31 PM.

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                  • #28
                    Check SMC_LID again, it should stay high. If it goes low then also EDP_BKLT_EN will go low.

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                    • #29
                      Well this ship has sailed. I'll be sending it you Mr. Robot.... I mean Mr. Rossmann LOL!! Hey at least you guys give great advice and then get more business when rookies like me can't fix it. On the bright side my Crest500HT showed up and I put a Macbook retina in it that would boot but had Vertical lines going up and down the screen. I was thinking it needed to be scrapped because I don't have a BGA machine to do GPU's (nor do I want to) so I threw it in the crest with some Branson and PRESTO! Working computer for free because a client just gave it to me for parts (didn't even want to spend the money on fixing) I've been testing it for 2 days and left on all night. I just have to explain that this computer had coffee spilled into it. Then the client put it in the oven at 100 degrees and forgot about it and it was actually on!!! I did recover the data from the HDD for him so not to bad.

                      So if it's a game to see who can fix the most computers this month its Crest=1 Me=0. Well played Crest. Well Played. LOL!!
                      Last edited by brooke.j; 10-11-2016, 05:05 PM.

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