Logic Board Question - 820-3115

Discussion in 'MacBook Pro' started by Mgm7890, Feb 9, 2015.

  1. Mgm7890 macrumors newbie

    Feb 9, 2015
    Hey everyone, first post, but been looking around here for awhile.

    I've come to an issue and would like some insight if someone can provide it. I have a MacBook pro that refuses to turn on (no chime, no backlight, No vcore power, no fan). It does have the green charging indication light.

    A few componets are blown, but they correspond to the battery circuit. I can go into my detail if need be on these.

    Anyway, I have no vcore power. I have schematics and board view, but I get no voltage at all coming from U1000 (the main CPU under the heat sink).

    Does anyone have an idea where to start? I'm just trying to get the fan to come back on at this point. Then work my way up.

    Thanks in advance! Sorry if I rambled or am a little scattered. Not sure how to start this questions or where to begin diagnosing.
  2. Mgm7890 thread starter macrumors newbie

    Feb 9, 2015
    Does anyone have an idea where to start if there is no vcore power?

    I'm trying to see if the board is dead or has a chance.
  3. Samuelsan2001 macrumors 604

    Oct 24, 2013
  4. Mgm7890 thread starter macrumors newbie

    Feb 9, 2015

    I did see that. I have another issues than that. It doesn't seem as simple as a resistor.

    But thanks for the input!!
  5. D. Mac Gregor, Feb 11, 2015
    Last edited: Feb 11, 2015

    D. Mac Gregor macrumors newbie

    Feb 9, 2015
    Hello Mgm, I am also a MacRumors newbie. How does your U7400 (CPU VCORE) and surround components look like? Anything burnt or missing?
  6. Mgm7890 thread starter macrumors newbie

    Feb 9, 2015

    My GH3 rails look fine through some fuses and resistors.

    Do you have a board to reference? I have the schematic and board view. A lot of my resistor values are way off under U1000. Also, some around the U7400 chip are wrong. They are like 1.2ohms vs the 150k or 75. The componets all look good, just weird readings on multiple. I can give specific resistor componet numbers if you have that ability to see. I doubt these 5 or 6 resistors are bad, so I'll keep looking at lines.

    The only thing that happens is just a green light from the AC power in. It's a steady green when just the board is connected (but no fan. Although the U1000 and U1800 Get hot). However, when I plug all the accessories in, the AC charging light flickers like a pulse response and makes a clicking noise (faint). So something is going on.

    It appears that some things may be missing. I can post a picture of what I see. I don't know the history of the board, but some components are definitely missing. I know that the first transistor and two resistors that are a part of the battery circuit is blown off. Also, a op-amp package and two resistors below the LVDS connector are gone.

    Thanks for your help!!
  7. D. Mac Gregor, Feb 12, 2015
    Last edited: Feb 12, 2015

    D. Mac Gregor macrumors newbie

    Feb 9, 2015
    Unfortunately, I don't have the schematic for your board. It's good that you have a green light on the adapter. but I assume the batteries are not getting charged? The resistors should have a tolerance as noted in the schematic...anything reading OL - I would replace if you have a donor board to compare resistances.

    Have you also checked all of your power supplies/rails? If the U1000 and U1800 are that Hot...I would suspect something is going straight to ground. What are the resistors reading between U1000 and VCORE?

    Work on getting that FAN to power up. Please post your pics on flickr or here...whichever is easiest. Man, where or who did you get this board from with all of those components missing?

    I am currently working on a 820-3209 water damage....:eek::apple:
  8. Mgm7890 thread starter macrumors newbie

    Feb 9, 2015
    It is my girlfriend's. I have no idea what happened to it exactly, haha. Just giving it a shot at resurrecting it.

    My VCORE to U1000 is 0. I attached an image of that area. The line points to where the measurement was taken. The circled area to the left is all places where resistors should be(?). I measure OL, but not sure if SMD components should be there, or if they are embedded pads. Is there a system to how apple just has their silver pads vs. components on the board? Finally, off to the right I get a few resistors that measure 0.2ohms. Far away from their 100 ohms. What would be making them pull down ohms so much? I can't remove them from the board to test, so not sure.


    U1000 definitely gets hot after about 10 seconds. The board gets rather toasty in that area.

    I get the 5V rail to the FAN. The FAN TACH connection is 3.3V, and the SMC_FAN line is around 0.05 (Not sure what this should be).

    As far as what is gone, the battery is non-existant. The plug-in to board leads must have shorted because the first resistor and transistor it sees is burned away. Also, another resistor further up is blown on CHRG_VFRQ.

    Finally, the FW Op-Amp is missing a leg, and two resistors. (But I doubt that any of those probably would cause the No fan, no chime, no anything. Or would it...?)

    Beside all that, the green light stays on fine, and the hard drive/ optical drive boot up when powered on.

    And good luck with your water damaged board! Hopefully it is something simple for your sake.

    Thanks again for your help D. Mac Gregor! I have faith in this :rolleyes:
  9. Mgm7890 thread starter macrumors newbie

    Feb 9, 2015
    The board does bootup using the procedure listed in another three on this forum about holding the power button on and then connecting the charger.

    The PCH still gets really hot, and I still have no VCORE. What is something to check with the PCH getting hot? There doesn't seem to be a stray path to ground.

    What would detail a bad SMC or PCH chip? Or do they not really go bad? I believe the way this all happened was with the shorting of battery terminals on the battery connector pins into the board.

    Any info about the PCH would be helpful! Also, on the SMC_onoff pads, I get a resistance of 18.2Kohms, where they should be 0 the schematic says. So, something is messing up the path, but it seems to lead into the SMC chip.

    Thanks in advance!

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8 February 9, 2015