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820-00034-A not turning on

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  • 820-00034-A not turning on

    Hi guys,

    I have iMac 21,5 820-00034-A logic board that doesnt turn on.

    1st led is on.

    G3 Rails are present,

    PP12V_S5, PP5V_S5, PP3V_S5 are presents too.

    ALL_SYS_PWRGD is 0V ( i have anothet working Mac with same board and ALL_SYS good is also 0V in S5)


    Any idea? What else i have to meausure. Tried SMC bypass not running.



    P.S: PM_SLP_S5_L is present 3.3V
    Last edited by BCN_Techs; 04-06-2019, 12:57 PM.

  • #2
    "PM_SLP_S5_L is present 3.3V"
    Then all S4 voltages should be present too; confirm that.
    If not, check for short at all S4 power rails; especially L7650.

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    • #3
      I see only 2 s4 voltages. PP5V and PP3V3 and both are not shorted and present when power supply connected. .

      Comment


      • #4
        Pm_slp_s4_l - 3.3v

        Comment


        • #5
          Also there is something happening that i have discovered just now. When plug cable iMac is entering s0 state, but no fan spins and only first led is on When press and hold power button for few seconds all s0 rails back to 0V again. The only rail missing is PP1V5_S0 ( not shorted to ground.
          Last edited by BCN_Techs; 04-09-2019, 10:15 AM.

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          • #6
            Check U7490 and U8440 voltages.
            Second LED requires ALL_SYS_PWRGD presence.

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            • #7
              U7490

              Pin 1,2,3,5 are 0V Pin 4 is 3.2 and Pin 6 1,8.

              U8440 board doesnt have it. I can see it in pdf too, but there is no componenten U8440 on it.


              P.S: U6200 was getting very hot. I removed it for now. Do you thinkg it can make machine not to turn on?
              Last edited by BCN_Techs; 04-09-2019, 10:49 AM.

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              • #8
                U8440 pads look untouched?
                It wasn't ripped off?
                C8440 is there?
                Do you get P3V3_S0_FET output voltage?

                Check for short (or low value) at C6203.
                Board should start if R6200 removed.

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                • #9
                  No informaticos, there is just no pads. Will attach photo tomorrow. It's strange because it's not "NO STUFF" just there is no componentes and pads there. WIll check all u wrote tomorrow. Thank you

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                  • #10
                    So the board doesn't correspond with schematic.

                    What about the other things mentioned in my previous post?

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                    • #11
                      sure, will do it tomorrow as promised thanks

                      P.S: at least in pdf there is 820-0034 mentioned in text so it's very strange

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                      • #12
                        So i have checked and:

                        it wasnt ripped off

                        there is no C8440

                        C6203 has low resistance to ground 120 OHMS ( checked with working logic board and it must have about 120Khoms).

                        There is no R6200. If you mean U6200 the board doesnt start with that removed.


                        Also U8400 seems to be blown. Dont have donor board so will wait untill it arrives me from China. Will back once put it again. Thank you 2Informaticos.

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                        • #13
                          I have recieved the U8400 and changed it. Again got 1.5V on PP4V5_AUDIO_ANALOG and almost shorted with 100 Ohms resistance to ground. Checked all and finally removed U6201 now get 4.5 instead of 1.5V and resistance to ground is ok. The question is, will iMac turn on without U6201?

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                          • #14
                            If is only audio circuit, board should start without it.
                            Nothing bad can happen if you try...

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                            • #15
                              PP3V3_G3 - 3.3V
                              PP12V is ok
                              PP3V42_G3H - 3.4V

                              PP12V_S5 - 12V
                              PP5V_S5 - 5V
                              PP3V3_S5 - 3.3V


                              PP5V_S4 -5V
                              PP3V3_S4 3.3V

                              PP1V8_S3 - 1.8V
                              PP1V2_S3 - 1.19V

                              The board is going to S0 state ( but only first led on it is on). So


                              PP12V_S0 - 12V
                              PP5V_S0 - 5V


                              PP1V5_S0 - 0V and nod shorted to ground. Checking line there is nothing wrong i can see using microscope It's not generated because of U8440 doesnt sent enable signal to U7490. The problem is that schematic and boardview i have there is no U8400 on real board. Already checked all avialable on internet and all are same.

                              P.S. I Found it. it's on the other side of the board near where it must be on boardview. If someone in the future check schematic will need this info. Now will continue checking.
                              Last edited by BCN_Techs; 04-30-2019, 09:23 AM.

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