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Apple macbook a1278 820-2936 need some help

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    #21
    Re: Apple macbook a1278 820-2936 need some help

    Maybe I'm missing something but there are no information about ISOLATE_CPU_MEM_L state at power-up (I'd think it's handled by the BIOS). So not much we can assume about it…
    The USB mouse trick is that on most optical mouses the LED will not light up if the BIOS is not POSTing (as the USB controller hasn't been initialized yet), it's only an additional hint to know what could be the issue.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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      #22
      Re: Apple macbook a1278 820-2936 need some help

      Isolate cpu mem l must be 1 for s0 state, as the page 30 of the schematic says...

      I’m missing ppvcore_s0_cpu ( and it’s shorted to ground 8.21ohms on the coils near cpu and 8.45 on the orher side of the board....

      I think this is a pain in the a*s ... i saw like 100 caps there (
      Last edited by justin35; 02-05-2019, 04:10 PM.

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        #23
        Re: Apple macbook a1278 820-2936 need some help

        As i am getting closet to the cpu the shor is at 8.07ohms...
        i think is a dead cpu?

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          #24
          Re: Apple macbook a1278 820-2936 need some help

          Ive never checked the line Isolate CPU mem for any macbook repair Im pretty sure thats not so important right now.

          I have the feeling you are looking for C while A and B are not even working yet.

          And 7 ohm IS NOT A SHORT on a CPU rail thats normal. The cpu takes more than 20 amps at 1,8V do the math

          And maybe it would help if you keep us posted about the things you do. Did you check bios area? Measure resistances to ground in diode mode and post values

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            #25
            Re: Apple macbook a1278 820-2936 need some help

            According to page 30 of the schematic... on the bottom of it, it says how the power on transition is happening from s0 to s3 and back to s0
            I have everything except isolate cpu mem l ...
            About the short, i figure it out, because it’s a low voltage high current line the resistance is low... if i had 100ohms at 1v... it was 100w of power which is outrageus
            So 8ohm at 1v results in 8w power which is normal.
            Also nothing was going hot...
            Anyway i came to conclusion u7400 myght be bad. It doesnt generate anything for q7250. No cpuimvp_ugate2, cpuimvp_phase2, cpuimvp_lgate2
            I will try and find one, maybe new because i don’t have a donor
            Last edited by justin35; 02-05-2019, 05:42 PM.

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              #26
              Re: Apple macbook a1278 820-2936 need some help

              Originally posted by justin35 View Post
              About the short, i figure it out, because it's a low voltage high current line the resistance is low... if i had 100ohms at 1v... it was 100w of power which is outrageus
              So 8ohm at 1v results in 8w power which is normal.
              Also nothing was going hot...
              Dont get confused mate but 1V at 8 ohm is 0.125W. Its actually voltage times amps not ohms. The resistance of the cpu goes less than 1ohm when active.

              Before you replace U7400 you should check the voltages on pin 1,2,40,24 to make sure it is told to turn on

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                #27
                Re: Apple macbook a1278 820-2936 need some help

                Yep you are right, i was confused!
                I'll check the voltages today and see if any is missing...

                Thanks!

                Comment


                  #28
                  Re: Apple macbook a1278 820-2936 need some help

                  Well i returned to this board today, i am missing pp3v3_s0...
                  It shows for a split of second, fan spins for a split of second also, then it goes 0.1v and stays there...
                  Pp3v3_s5 is present 3.3v
                  P3v3s0_ss is present 3.3v

                  Is it a bad q7830?

                  Because of this is missing pm_slp_s4 right?

                  Ps: if i short pp3v3_s5 with pp3v3_s0 can i damage anything?, just to see if it starts... i don’t have sia427dj to replace and see if it works
                  Last edited by justin35; 02-14-2019, 01:01 PM.

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                    #29
                    Re: Apple macbook a1278 820-2936 need some help

                    So something changed from before? Are ALL_SYS_PWRGD, PM_PCH_SYS_PWROK and CPU VCore spiking as well?
                    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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                      #30
                      Re: Apple macbook a1278 820-2936 need some help

                      Well this board is nasty...
                      It went from fan spin on/off and so on, to a full fan speed...
                      It’s something that is not attached properly to the board, because flex the board easely it starts full fan speed and stays there...
                      When it was pulsing i noticed it was missing cpu_imvp_vswg, which is also missing when full fan spin is present.
                      Also when pulsing the cpuimvp_vr_on was pulsing, but when full fan speed is present, it’s 3,27v always.

                      On u7400 which i got from a donor board, because the original one was bad, it’s missing:
                      Cpuimvp_phase1g
                      Cpuimvp_ugate1g
                      Cpuimvp_lgate1g

                      I do have pp5v_s0 5.02v and cpuimvp_boot1g 4.69v

                      Cpuimvp_vr_on is enabling the other cpuimvp phase and boot 1 right?
                      This lead me to think i have a faulty u7400?(isl95231)?

                      Ps: allsys_pwrd_gd and pm_pch_sys_pwork were ok on pulsing fan and still ok on full speed fan
                      Last edited by justin35; 02-15-2019, 10:30 AM.

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                        #31
                        Re: Apple macbook a1278 820-2936 need some help

                        Ok, so i have now ppvcore_s0_cpu_ph1 And 2 but no chime, no image no nothing... just a gradual fan spin up to full speed... no missing ram beeps
                        Any idea?
                        Pch is getting worm, cpu as well...
                        Cpuimvp_vswg 0v
                        Cpuimvp_phase1g 0v
                        Cpuimvp_ugate1g_r 0v
                        Cpuimvp_lgate1g 0v
                        Last edited by justin35; 03-14-2019, 04:38 PM.

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                          #32
                          Re: Apple macbook a1278 820-2936 need some help

                          CPUIMVP_PHASE1G = PPVCORE_S0_AXG_REG So it won’tcome up until internal screen is connected.
                          That is one problem solved!
                          All sys power good is 3,3v
                          All thevoltages are present...

                          Bios was flashed with one from this forum, nothing changed...

                          Bad smc?

                          Comment


                            #33
                            Re: Apple macbook a1278 820-2936 need some help

                            PRAM reset done? (I guess it won't respond if it's not even doing RAM beeps without RAM — assuming speakers are plugged in —)
                            PLTRST# at 3.3V?
                            Any activity on BIOS? (oscilloscope on CS# with trigger set to single shot on falling edge should pick something)

                            Still try another EFI, you never know someone may have posted a bad one…

                            If everything is ok, could be bad SMC, bad PCH, bad CPU… random thing somewhere like blown or missing resistor on a data bus… Depends on the history of the board.

                            Could also check for activity on the LPC bus (communication between SMC and PCH), the 4 LAD data lines and the LFRAME# signal.
                            OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                            Comment


                              #34
                              Re: Apple macbook a1278 820-2936 need some help

                              Can’t reset PARAM...
                              Bios:
                              Pins 1,2,3,7,8 constant 3,3v
                              Pins 5,6 just a flash of 3,3v (measured on another working board and it’s the same)

                              I will try another efi today, first i have to find another one

                              Comment


                                #35
                                Re: Apple macbook a1278 820-2936 need some help

                                pls send back-up bios pls

                                Comment


                                  #36
                                  Re: Apple macbook a1278 820-2936 need some help

                                  here's the attached bin file.
                                  i also got a corded mouse plugged in and nothing on the mouse light....
                                  Attached Files

                                  Comment


                                    #37
                                    Re: Apple macbook a1278 820-2936 need some help

                                    I found on rossman forum a simillar issue with different board model, and reballing emc solved the issue...
                                    I haven’t done this kind of job for an smc, but before i do it, i must be sure the problem is not caused by something else

                                    Comment


                                      #38
                                      Re: Apple macbook a1278 820-2936 need some help

                                      I mean reballing SMC NOT EMC...

                                      Comment


                                        #39
                                        Re: Apple macbook a1278 820-2936 need some help

                                        Well, still no luck with this one...
                                        I took out smc and reballed but still nothing
                                        I assume the reball is succesfull because i have green light, fan spin as before, but still no chime (((
                                        Any other suggestion??
                                        Thanks!

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                                          #40
                                          Re: Apple macbook a1278 820-2936 need some help

                                          Now i have 3 820-2936 boards with the same issue...

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