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  1. #1
    A1260 no lights on charger
    I have a MacBook pro A1260 (820-2249A board) as a project to get up and running. I have checked the board and PPBUS_G3H and PP3V42_G3H are both present.

    I have found a resistor with a curious reading and I wondered if anyone could advise if it is faulty

    The resistor is R5075, with PP3V42_G3H on one side, and SYS_ONEWIRE on the other. With no power to the board, the resistor reads 2k ohms, are per the schematic, however when power is applied to the board, the resistor reads 5.9m ohms and the SYS_ONEWIRE side of the resistor reads output of only 0.47v.

    All the other resistors in the area that have PP3V42_G3H on one side all read the same approx the same as the schematic (powered or not)

    I'm not an electronics specialist, but my thoughts are that the resistance shouldn't change that significantly?

    Thanks in advance for any help.

  2. #2
    A1260 no lights on charger
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
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    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 7+, iPhone 8, Numerous iPods, Catalina
    Rep Power
    55
    Welcome to our forums.

    Unfortunately, we do not have access to schematics for any of Apple's devices. As you probably know, only authorized Apple Repair Service Centers and genius bars are supposed to have access to them.

    As a retired electronic tech, I can verify that measuring components while power is off is sometimes quite a bit different than when power is applied.

    I'm assuming the MacBook Pro you're working on is not charging? What exactly is it not doing and what have you tried so far? Also, model A1260 tells me that it's an early 2008 15" MacBook Pro.

    Let us know and we can go from there.

  3. #3
    Quote Originally Posted by chscag View Post
    Welcome to our forums.

    Unfortunately, we do not have access to schematics for any of Apple's devices. As you probably know, only authorized Apple Repair Service Centers and genius bars are supposed to have access to them.

    As a retired electronic tech, I can verify that measuring components while power is off is sometimes quite a bit different than when power is applied.

    I'm assuming the MacBook Pro you're working on is not charging? What exactly is it not doing and what have you tried so far? Also, model A1260 tells me that it's an early 2008 15" MacBook Pro.

    Let us know and we can go from there.
    That’s right it is an early 2008 15”.

    There are no lights on the charger and to power up I have to hold down the power button for 10 secs, then plug the charger in, while stills holding the power button for another 10 secs. After that I can start by just pressing the power button. I have tried the smc reset and I still have to follow the same start procedure.

    The only thing I can find that appears to be odd on the board is this resistor

  4. #4
    A1260 no lights on charger
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
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    59,763
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 7+, iPhone 8, Numerous iPods, Catalina
    Rep Power
    55
    It may be difficult to find replacement parts for a machine that's 12 years old. The only thing I can suggest is to try another charger if possible. Also, the DC input board is sometimes the culprit with what you described. But, I would also look at the condition of the battery.

    I don't remember off hand if that model will start without a working battery. Most later models will not, some earlier models would start but run very slowly due to throttling of the CPU.

    Worse scenario is a bad logic board.

  5. #5
    A1260 no lights on charger
    krs's Avatar
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    Quote Originally Posted by SiPreston73 View Post
    I have found a resistor with a curious reading and I wondered if anyone could advise if it is faulty

    The resistor is R5075, with PP3V42_G3H on one side, and SYS_ONEWIRE on the other. With no power to the board, the resistor reads 2k ohms, are per the schematic, however when power is applied to the board, the resistor reads 5.9m ohms and the SYS_ONEWIRE side of the resistor reads output of only 0.47v.
    My first question would be: "How do you measure the value of the resistor?"

    You usually can't just use an ohm-meter and measure the resistor in the circuit unless you have a schematic and can verify that there are no sneak paths that distort the measurement.
    To get an accurate reading one would need to unsolder one end of the component and then measure.

    And you certainly cannot get accurate resistor value readings with an ohm-meter and the circuit powered.

    If you have a schematic, it should show you test points and the expected voltage at each of those test points - that's the first thing I would verify.
    And if the test point voltage you measure (with a GOOD meter) doesn't match the value on the schematic, that's the area you want to investigate.

    Knut

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