2009 A1278 Logic Board Question, Steady White LED no Chime.

Discussion in 'MacBook Pro' started by rsximus, Nov 2, 2011.

  1. rsximus macrumors newbie

    Joined:
    Mar 22, 2008
    #1
    I'm working on two A1278 Macbook Pro Logic Boards with the same exact issues. They both had water damage, cleaned up both boards in alcohol, they power up, battery is charging, fan is on full, the HD spins up but the white LED indicator in the front of the case just stays solid in the front. No Chime, blank screen.

    I'm guessing the SMC circuit has sense a failed self test so it won't allow the unit to boot up. Can anyone, hopefully cmdrdata or Dadioh or any of the other super knowledgeable guys on here point me in the right direction? I have schematics for both the 13" and 15" Macbook Pros but have no idea where to start looking.....

    Any help would be super appreciated!
     
  2. Mikf macrumors newbie

    Joined:
    May 9, 2012
    Location:
    The Netherlands
    #2
    Sorry for the bump, but I'm having the exact same problem with a mbp 13" early 2011. It turns on, the fan goes to full speed, but no chime or screen. Are there any parts on the logic board that i can measure?
     
  3. kvtec21 macrumors newbie

    Joined:
    Sep 3, 2012
    Location:
    Bremerton, WA
    #3
    Macbook Pro MB991LL/A-Powers On-No Chime-No Video-Fan, HDD, Optical Drive Work

    Any luck in finding the cause of the problem and a potential fix? I too am experiencing this problem with my A1278. I'm considerably new to the "Mac World" as an owner anyway, about five months or so, but have been working with pc's for some time now. I'm hoping to finally be a part of the team to remedy this issue as I have not found a solution to this specific problem anywhere on the web.

    Here's a brief description of my problem:

    -Powers on and stays on with no chime, no boot, no video as well as backlight
    -Hard drive, optical drive and fan start
    -Power/sleep led on front stays on constantly lit
    -Battery charges

    Here's what I have done/tested/observed:

    -Problem still occurs after resetting PRAM and SMC
    -Charger adapter, ram slots and ram has been confirmed as good
    -SMC seems to be operating or partially operating (this is based off of a ram test I conducted by removing both ram sticks followed by SMC reset; SMC detects no ram in slots and beep error occured)
    -Confirmed power is being received by the hard drive, optical drive, fan and battery charging
    -Speakers and headphone jack appear to be working
    -Led backlight fuse has been tested for continuity and voltage
    -WLED driver has not been tested (kinda scared of checking the enable pin at this point in time because the pins are a little too close for comfort! lol! this is definitely one of my next challenges to rule out the WLED driver itself) As far as the WLED driver is concerned, it appears in tact visually with magnification. I did confirm that the boost diode is not boosting the power to the specified 27V as needed to power the display. This circuit seems to be one of two possible culprits contributing to this issue we're having with no startup chime and boot. Especially if it's one of the "checklist items" for the SMC. My next step of troubleshooting this circuit is to check continuity in each resistor within this circuit (both before the WLED driver as well as its return).
    -The second culprit I'm referring to is the GPU. I do not have the necessary adapter to confirm whether or not it is providing video on an external monitor. This is also on my list of things to do. However, based on my experience these symptoms could possibly be related to a faulty GPU. (Anything from a bad chip, cold solder joint or bridged solder joint???)

    Here are a couple of questions I have for anyone who is gracious enough to assist:

    -Is the WLED driver part of the SMC's "checklist"? If so, could this be the reason for no startup chime and boot?
    -I have repaired other macs in my years of experience including correcting problems with GPU's. I do believe that the systems I have repaired (at least a few of them that I recall) with GPU issues were able to boot with a startup chime even with a faulty GPU. My question is, Is the GPU part of the SMC's "checklist" for startup that would prevent a successful startup chime and boot?

    I am new to this forum as far as being a registered user. However, I have been following it for about a month an a half in hopes that someone may be able to shine some light on things and find a solution to my problem. This is the only forum I have come across that has addressed this issue I'm having, in broken parts anyway, and I'm very hopeful that this issue will soon be remedied.

    Thank you in advance!

    ----------

    Any chance you could upload the schematic for the 13" MBP and provide a link? Thank you.
     
  4. kvtec21 macrumors newbie

    Joined:
    Sep 3, 2012
    Location:
    Bremerton, WA
    #4
    Solved!

    I'm not quite sure if this will remedy anyone's problem as it did mine, but after extensive testing the problem I had was repaired for just under $19 by ordering and replacing the GPU. I was able to come to this conclusion after testing the WLED driver, display, display cable, continuity and voltage testing throughout the WLED driver circuit with all normal readings and results. It was at that point in time when I decided to attempt a reflow and was partially successful when the display flickered and showed some sign of life. I concluded that the solder connection to the GPU was compromised. I do not know if it was simply a cold or bridged joint or a bad GPU . However, I do know that by replacing it completely along with a fresh set of solder balls fixed this issue.
     

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