MacBook Pro Unibody - No Backlight - Logic Board Question

Discussion in 'MacBook Pro' started by Dadioh, Jul 20, 2010.

  1. Dadioh, Jul 20, 2010
    Last edited: Sep 20, 2012

    macrumors 65816

    Dadioh

    Joined:
    Feb 3, 2010
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    Canada Eh?
    #1
    IMPORTANT NOTE: Further in this thread you will read that this part is a high frequency capacitor. IT IS NOT A FUSE!!! PLEASE do not go about replacing this part with anything other than a capacitor. READ CAREFULLY the whole thread before messing around with component substitutions.


    Original post
    ----------------------------
    I obtained a Macbook Pro 13 unibody with non functioning display (everything else works). I took it apart ad discovered that the LVDS cable end was completely destroyed. I ordered a replacement display assembly (complete with LVDS cable). I now have an image but no backlight.

    Upon close examination of the components surrounding the LVDS connector I notice I have a component missing compared to a detailed photo of the same motherboard that I found on the net. I am not sure if this component might be a fuse that has been removed. I am trying to find someone who has one of these logic boards accessable that can identify what this part is supposed to be.


    Update: There are many many more tips and info in this thread to help you with troubleshooting backlight issues on Macbook Unibody.

    In particular the WLED driver should be checked for failure. A useful method is to test the resistance (impedance) from each pin of the WLED driver device to ground. Typical values are shown below.

    Make sure power is removed from board before testing resistance. Unplug battery or battery connector.

    Macbook Pro 13"
    Device LP8543 Pin 1 is lower left and counts counter clockwise around the device.
    Pin Resistance to ground
    1 0
    2 1K
    3 124K
    4 100K
    5 0
    6 >1M not connected
    7 >1M
    8 19K
    9 0
    10 not connected
    11 21K
    12 >1M
    13 >1M
    14 >1M
    15 0
    16 >1M
    17 >1M
    18 >1M
    19 not connected
    20 0
    21 >1M
    22 203K
    23 400K
    24 290K


    On Macbook 13 unibody aluminum non-Pro
    Device APP001A

    1 3.8M
    2 100
    3 9.9M
    4 46K
    5 100K
    6 100K
    7 >10M
    8 49K
    9 69K
    10 >1M
    11 >1M
    12 >1M
    13 0
    14 >1M
    15 >1M
    16 2.8M
    17 10K
    18 15K
    19 34K
    20 30K


    If your WLED driver is blown you may measure zero or low resistance on some of the pins that are not supposed to be ground.
     

    Attached Files:

  2. macrumors 65816

    Joined:
    Jul 16, 2010
    #2
    why not just bring it to apple?


    did you buy it on Ebay or something?
     
  3. macrumors 6502

    Joined:
    Nov 7, 2007
    #3
    I suspect because Apple will tell him that is an unauthorised user repair and needs a whole new logic board....which is $$$$ / ££££/ €€€€
     
  4. macrumors 65816

    Joined:
    Jul 16, 2010
    #4
    You would have to be a moron to not realize that taking apart the entire computer voids the warranty. The only thing that doesn’t is upgrading the HDD and ram.

    so I’m wondering why he still did it.
     
  5. thread starter macrumors 65816

    Dadioh

    Joined:
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    Canada Eh?
    #5
    Got it on eBay as an as-is special. Everything working except the display. Was a mid 2009 and not under warranty anymore. When I took it apart the LVDS connector end was ripped apart. Looks like a botched repair job by someone. So I looked for a used LVDS cable but was unable to find one (they are sold as part of the complete display assembly). Because I got the unit cheap enough it was worth it for me to pickup a complete display assembly. However, the backlight was not working after doing the repair. Given that I have no idea what the previous "repair" attempted was, I can not rule out the removal of this component.

    I am looking for the help of someone that knows the right end of a multimeter to measure the component in question and tell me what the value is. Maybe this is the wrong forum given the "moron" accusation. Considering I am an experience electrical engineer with design background I would guess the accusation is just a "little" off base. Maybe I will try the question in a forum of like-minded repair oriented people.
     
  6. thread starter macrumors 65816

    Dadioh

    Joined:
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    #6
    Before you toss around "moron" labels why not find out the background. Thanks for the excellent help :rolleyes:
     
  7. macrumors 65816

    Joined:
    Jul 16, 2010
    #7
    sorry, you hadn’t responded, so I was just throwing the possibility out there...

    I apologize if I pissed you off. You might want to check ifixit.com. Im afraid I cannot be of much assistance (as you may have already assumed).
     
  8. thread starter macrumors 65816

    Dadioh

    Joined:
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    #8
    No worries. I already have this posted at iFixit. I was doing a quick google search on macbook logic board repair and came across a similar question on this forum so I thought I would give it a shot.

    I may end up buying another as-is MBP just to add to my inventory of parts and provide the answer to my own question. However, if there is another hobbyist out there that has one of these boards at the ready they could take a 20 second multimeter measurement for me. Here's hoping.

    Peace
     
  9. macrumors 65816

    Joined:
    Jul 16, 2010
    #9
    MacBook Scramble: Build It Yourself Edition
     
  10. thread starter macrumors 65816

    Dadioh

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    #10
    :D

    It's a hobby...
     
  11. macrumors 6502

    Joined:
    Oct 1, 2007
    Location:
    Los Angeles, CA
    #11
    did u ever figure it out? im having the SAMe exact issue.
     
  12. thread starter macrumors 65816

    Dadioh

    Joined:
    Feb 3, 2010
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    Canada Eh?
    #12
    Still working on it. The part in question is a 4.7uF 50V capacitor and is part of a boost circuit made by National Semiconductor. Basically I am not getting the voltage input to the circuit and I am trying to trace back to see if there is a blown fuse. Haven't had time to spend on it though.

    http://www.national.com/ds/LP/LP8543.pdf

    You will need some electronics skills and a good multimeter to sort through this I expect.
     
  13. macrumors newbie

    Joined:
    Sep 29, 2009
    Location:
    Finland
    #13
    I can send you a schematic of MacBook pro 15" unibody Late 2008, if that would help you out?

    On my board all white components are fuses.

    -Jan
     
  14. thread starter macrumors 65816

    Dadioh

    Joined:
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    #14
    That would be awesome. It may give me the info I need for how they power the device. How can I arrange to get it from you?
     
  15. macrumors newbie

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    #15
  16. thread starter macrumors 65816

    Dadioh

    Joined:
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    #16
    WOW! Thanks. That should do the trick. I suspect that the 15" and 13.3" will not be all that different in how they designed the power input to the WLED boost circuit. That is really helpful. :D
     
  17. macrumors newbie

    Joined:
    Sep 30, 2010
    #17
    no backlight on macbook pro 15 unibody

    OK for all the people with no backlight on a macbook pro 15" unibody.

    first of all thanks to the man with the schematic....
    I take it you have checked the flurecent and inverter allready and both are ok.
    on the logic board there is a fuse that supply's the voltage/ currant to the backlight circuit...its F9800.Its located on the board near the botom of the left fan on the component side of the board.(same side that has the cpu and gpu on it).

    the fuse is a smd and its white with just a dot on it.get your multimeter and if its open circuit thats you problem.
    got mine fixed today...

    If you need a hand then drop me a line and i will try to see what i can do...

    Had to share this as it took me a good day to put right,,,

    good luck.

    componentfix
     
  18. macrumors regular

    armoredsaint

    Joined:
    Sep 7, 2010
    Location:
    USA
    #18
    are you sure it's not stolen? with my undercover anti-theft i can make it fake a hardware failure with the screen not turning on.

    so when it's taken to an authorized apple center, they can tell it's been stolen.
     
  19. thread starter macrumors 65816

    Dadioh

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    #19
    On the 13 MBP it is actually on the other side of the board from the CPU and GPU which makes it very convenient to check. It is a 2A fuse in an 0402 package so it is tiny. Fortunately I have a stereo microscope that I use for soldering :)
     
  20. thread starter macrumors 65816

    Dadioh

    Joined:
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    #20
    No. This was actually a blown WLED driver device. I replaced it and got my backlight back ;)

    I can see how it would be possible for a SW program to tell the WLED driver not to enable since that is exactly what can be done with the F1 and F2 keys on the keyboard.
     
  21. macrumors newbie

    Joined:
    Sep 23, 2010
    #21
    Cool so you got all that fixed, up and running? How much did everything cost you? =D
     
  22. thread starter macrumors 65816

    Dadioh

    Joined:
    Feb 3, 2010
    Location:
    Canada Eh?
    #22
    Well I ended up about breaking even I would say. Lots of hours to figure out how that circuit worked and then removing and soldering on a QFN package. :rolleyes:

    http://en.wikipedia.org/wiki/Quad_Flat_No_leads_package
     
  23. macrumors 6502a

    lPHONE

    Joined:
    Nov 17, 2009
    #23
    Led backlit displays do not use inverters

    you get as-is things like this on ebay for low prices because they're broken, not stolen. :rolleyes:

    where do you people come from? you just bust out and "blah blah"
     
  24. macrumors newbie

    Joined:
    Oct 7, 2010
    #24
    Similar problem!

    i have a similar problem,
    i have a Macbook A1181 13 2.0GHz with a non working monitor,

    after power-on i get a half second flash light from the lcd and from the led light web-camera
    and i cant see any image at all (no faint images or back light) from the monitor

    i already replace the inverter, still the same symptoms
    i think it is the logic board
    after make some tests with a voltimeter on the cable from logic board that goes on inverter i can see the same symptoms on the voltimeter (the voltage go high for half a second)

    i don´t have a video rgb cable to hook the computer to a external monitor

    here my targets:

    - it is a bad inverter cable?
    - it is a bad logic board?
    - it is a smd fuse on logic board?
    - it is a Missing enable voltage from motherboard's video chip?

    My last option is to replace the logic board
    but before i want to try to fix my self


    tanks every one
     
  25. macrumors newbie

    Joined:
    Oct 8, 2010
    #25
    No backlight MB13 unibody

    @Dadioh,

    I have been aiming my efforts at the QFN package also until I came upon this thread. I have a fuse (closed) on the MB but it's not as small as described above. Can you give me a description of where about on the MB you found the tiny fuse. I'm at my macbook for at least two weeks now with no luck. Tks.
     

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