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820-3662 PPBUS, 5V_S5 and 3V_S5

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  • 820-3662 PPBUS, 5V_S5 and 3V_S5

    Liquid damaged board.

    Looks to have been cleaned with IPA but still shows liquid signs

    Crusty around Q8060 and Q8052 replaced
    Also C7317, C7318, C7319 replaced C7317 was particularly fucked.
    U7310 replaced.

    PPBUS = 3.9V
    PP5V_S5 = 3.9V
    PP3V3_S5 on scope hits 3V3 and slopes down. Cycles.

  • #2
    Do you get light on MagSafe?
    PPBUS_G3H and PP3V42_G3H stable?

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    • #3
      Originally posted by 2informaticos View Post
      Do you get light on MagSafe?
      PPBUS_G3H and PP3V42_G3H stable?
      Yes stable 3V42, yes green / orange
      PPBUS 3.9V
      Last edited by G.Beard; 03-07-2017, 10:46 AM.

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      • #4
        Changed 6259
        PPBUS_G3H is back
        5V_S5 is back stable 5V.

        3V3_S5 is 0V on scope
        Short on 3V3 someplace
        Last edited by G.Beard; 03-07-2017, 10:50 AM.

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        • #5
          PP3V3S5_EN present??? Resistance to GND on PP3V3_S5??

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          • #6
            3V3S5_EN = 3V3
            3V3_S5 = 4.2Ohm
            Last edited by G.Beard; 03-07-2017, 11:17 AM.

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            • #7
              Did you measure resistance with no power applyed and waiting for a moment for the circuit to discharge???

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              • #8
                Originally posted by aprendiz View Post
                Did you measure resistance with no power applyed and waiting for a moment for the circuit to discharge???
                Yep. It's 4.2Ohms so I guess I'll just wack some Amps through it and see what gets hot.....

                However this is not making sense as earlier 3V3_S5 was cycling.
                Last edited by G.Beard; 03-07-2017, 12:49 PM.

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                • #9
                  Ah. My bottom lip just detected a short through U1900
                  Replacing U1900 did not work!
                  This new U1900 is getting hot too.
                  Last edited by G.Beard; 03-07-2017, 01:16 PM.

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                  • #10
                    Is PPVRTC_G3H shorted to ground?

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                    • #11
                      Yep just found that one.. As well as PP1V5_S0.
                      Last edited by G.Beard; 03-08-2017, 10:55 AM.

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                      • #12
                        Remove U1900 and see if the short is under the chip. PP1V5_S0 is going to have a low resistance to ground because it is a low voltage line powering a high powered large BGA.

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                        • #13
                          Originally posted by larossmann View Post
                          Remove U1900 and see if the short is under the chip. PP1V5_S0 is going to have a low resistance to ground because it is a low voltage line powering a high powered large BGA.
                          No short under U1900 and PPVRTC still shorted without U1900 on the board. Caps on PPVRTC are all fine. 3V3_S5 also shorted. I had already restored PPBUS and 5V_S5.

                          This is a bit long now.
                          Your help is much appreciated... But fuck this board man.

                          Many thanks all.
                          Last edited by G.Beard; 03-08-2017, 11:20 AM.

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                          • #14
                            what I do with rabbit holes is just start removing everything that could be pulling down the voltage or shorting to ground, if that doesnt work start removing bits that lead to other lines, one job of mine today was like that, one of the 1v s0 rails was shorted to ground, pretty much everything removed and still there, only thing left was the cpu, customer called, is now in the bin

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                            • #15
                              I removed the caps on PPVRTC and the U1900 and it was still short on PPVRTC so we'll call it an expensive Frisbee.

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