Macbook Pro mid 2010 resistor values

Discussion in 'Mac Basics and Help' started by Shaky McSoldering, May 12, 2016.

  1. Shaky McSoldering macrumors newbie

    Joined:
    May 12, 2016
    Location:
    London
    #1
    Hello,
    I am an ex-lurker, sub-genius type person who is trying to repair a MBP that appears to have a few problems.

    I can't seem to find a dedicated mothrboard repair forum here, so apologies for the inappropriately positioned new thread, if anyone can suggest a better place for it I would be glad to delete/move the post.

    The first problem that there is no light on the magsafe connector.

    I do have Board View and schematic files for the motherboard which is an:

    A1286 - EMC 2253 - 820-2850-a - K18.

    I am going through the G3 Hot circuit diagnosing the components but I notice that my schematic PDF (pg. 64) does not specify the resistances for some of the resistors.

    For example R6990, R6992 and R6993 are specified as

    '''5%

    MF-LF

    1/16W

    402'''

    This gives me a lot of useful information, but no Ohm value to measure.

    I have looked at the schematics for other MBP boards, some have the Ohms, but the circuits are different and include diodes.

    Could someone please help me with the resistance values for these components?
     
  2. MacTech68 macrumors 68000

    MacTech68

    Joined:
    Mar 16, 2008
    Location:
    Australia, Perth
    #2
    I could be reading it wrong, but if you look a little closer, you'll see a 0 (zero) above R6993, a 1 above R6990, and a 0 (zero) above R6992.

    I'm going to assume these are the values in Ohms, so

    R6990 = 1 Ohm 1/16W 0402
    R6992 = zero Ohm 1/16W 0402
    R6993 = zero Ohm 1/16W 0402

    I guess it's just the strange way it's annotated. I must admit, it had me for a short while. :)
     
  3. Shaky McSoldering thread starter macrumors newbie

    Joined:
    May 12, 2016
    Location:
    London
    #3
    Thanks for the reply!
    I did see the ones and zeros on the schematic, but they seemed fishy to me.

    All the other resistances that I checked in the 100+ page document did specify the unit, so I thought it was a misprint.
    thinking maybe my schematic is a hokey pre-production version.

    I am too much of a scared newb to replace the components without the validation of someone who knows better.

    Mr. Rossman does say that the first two resistors are basically fuses, so maybe I will give it a go.
    I just don't want to end up doing more expensive damage.

    My basic problem is that PP3V42_G3H is giving me .612 volts at probe point 918.
     
  4. MacTech68, May 12, 2016
    Last edited: May 12, 2016

    MacTech68 macrumors 68000

    MacTech68

    Joined:
    Mar 16, 2008
    Location:
    Australia, Perth
    #4
    A simple check with a multimeter should tell you if those resistors are OK.

    Good tips here if you haven't seen it already:

     
  5. Shaky McSoldering thread starter macrumors newbie

    Joined:
    May 12, 2016
    Location:
    London
    #5
    Ah yes, but I needed to know the reference values,
    which as far as I was concerned were not on the schematic.

    What I see is:
    R6990 1.2 ohms
    R6992 .3 ohms
    R6993 .2 ohms

    If the ones and zeros theory is correct (which seems very likely) and the tolerances are 5% then all of these look like they need replacing.
    I would love to see what a fresh 0 Ohm resistor should read on a meter, as in what is 5% of zero?

    Some new ones are on the way anyway, hopefully I will have them for the weekend.
    I will let you know how I get on, thanks for the help.
     
  6. chown33 macrumors 604

    Joined:
    Aug 9, 2009
    #6
    Zero ohm resistors are cheap. Touch the probes of your meter together. What's the reading?

    Probe cables have non-zero resistance.
     

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