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820-3476 No PPBUS No PP3V42

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  • 820-3476 No PPBUS No PP3V42

    Doesn't Turn ON no Green Light No History

    Q7010 and R7020 Burning Hot
    Replaced U7090: OK not burning anymore

    PPBUS: 0V

    R27/28: OK

    Checked the voltages at U7100:
    1: CHGR_AGATE 0V
    2: CHGR_DCIN 16.30V
    3: CHGR_ACIN 3.950V
    4: CHGR_VFRQ 0.170 VS
    5: CHGR_ICOMP 0V
    6: CHGR_CELL 0.170V
    7: CHGR_VCOMP 0V
    8: CHGR_VNEG 0V
    9: CHGR_AMON 0.031V 0.031V
    10: SMBUS_SMC_5_G3_SDA 0V
    11: SMBUS_SMC_5_G3_SCL 0V
    12: PP3V42_G3H 0.177V

    So I checked my soldering job at U7090:
    I've re heated with the hot air, it moved a little bit then the PP3V42 voltage rised to 2.5V
    but on Pin 6 the voltage dropped from 16.5V to 3.7V -3.21V

    Checked again R7020: Burning hot again.

    I think my U7090 is bad again, if so , why?

    Stupid Question: Which rail should be present first PPBUS or PP3V42?
    I would say both at the same time, which would mean that I have 2 issues so far on that board?
    Maybe U7100 is pulling down PP3V42?
    Last edited by Bouba148; 5 days ago.

  • #2
    First of all, check diode mode to ground at L7095 and L7130.
    If you found R7020 burnt, check if D7005 is not shorted (both sections).
    Check al caps C7090-92.
    Be sure R7095/96 are both OK.


    • #3
      Hi 2Informaticos,
      I've already did all those checking but because of you, I've redone them and thank you because I've read 0.140V at F7140 (removed) but in the rush I've swapped the pins so I went in the wrong direction.
      this value is in the direction of L7130 and U7100, by the way this one (U7100) is removed, so I would suspect Q7130 because I still have 0.146V at Pin 1 of L7130 with this one removed.
      What do you think?


      • #4
        Replaced Q7130 but still the same reading value of 0.140V, so I checked some other motherboard of the same generation, and it appear that at L7130 they all read the same value.
        So now I'm confused because on pin 2 of F7140 i'm reading 0.465V.
        And No short on C7090-92, no short at D7005.
        R7095 reads 190KOhms and R7096 155kOhms both are low compared to the schematics but wompared to some other boards I have more or less the same reading.


        • #5
          3v42 MUST be present before PPBUS is 3v42 3.42? If no probably bad U7090.


          • #6
            Replaced U7090 3 times now, still PPVIN_G3H_P3V42G3H dropping from 16.5V to 3.2V and R7020 burning hot.
            Replaced C7095, R7095, R7096.
            When removing u7090 PPVIN_G3H_P3V42G3H : 16.5V
            I'm confused any clue?
            U7100 is removed also.


            • #7
              Did you place U7090 in correct way?
              Be sure C7094 is OK and has good contacts.
              If not, U7090 gets fried.

              Low-side MOSFET from Q7030 is Schottky, so diode mode to ground value is correct.


              • #8
                yes U7090 is soldered corretly, when you turn it upside down there is a mark on the ground pad that matches to the ground pad on the motherboard.
                I've put another LT3470 from a donor board and still the same ( now 4 + the original one that I've put in the trash).


                • #9
                  Your VIN pin should not be fluctuating something is wrong there. Check that pin for a short could have problems before or after the diode. Q7080 is also suspect here. Make sure traces to U7090 are good as well


                  • #10
                    Hi JohnB8812,

                    Sorry but my Vin,is not fluctuating, it's just that when I've writen that it's "dropping", I would better write : I'm mesuring 3.2V instead of 16.5V when U7090 is soldered.
                    Something is pulling down my Vin, and that thing is not on the Ppbus_g3h side but on the Pp3v42 side when looking from the diode "Y" path.
                    Maybe I should start by that DIODE D7005 ?


                    • #11
                      For your VIN being low, something is going wrong on 3V42 circuit, check carefully all resistors caps around U7090.

                      Nothing wrong, no short with pp3v42_g3h rail?

                      Yes you can disconnect R7005 to isolate ppbus_g3h. You can also remove D7005 and inject 16,5V on pad 3 of removed D7005 and check how PP3V42 circuit behave.


                      • #12
                        Did you put correct (47 ohms) for R7020?
                        Check if is not 47 ohms, or 47K.


                        • #13
                          20190318-115723-176.jpg Sure, It's a 47 Ohms R7020 reading 47.6 Ohms that I've already replaced because the original one was OK but started to turn brown because of over heating.
                          Also just replaced D7005 just in case, but didn't change anything.
                          I think I'm missing something obsvious but can't see what.
                          I took an U7090 from a known good board and still the same:
                          PP3V42: 2.5V
                          PPVIN_G3H_P3V42G3H: 3.31V
                          R7020 burning Hot
                          Checked all the tracks around U7090, replaced almost all the components around U7090.
                          Again if I remove U7090 R7090 is NOT heating and PPVIN_G3H_P3V42G3H is 16.5V
                          PP3V42 is NOT shorted to Gnd as in diode mode I read 0.313V
                          I'm out of ideas.
                          Also I did te following test:
                          Removed U7090, injected 3.42V (300mA)
                          Plugged In the charger
                          I Still I had No PPBUS_G3H but SMC looks like OK becuse I have SMC_BC_ACOK, SMC_BC_ACOK_VCC, SYS_ONEWIRE and ADAPTER_SENSE present.
                          The green Light is very DIMM
                          Maybe I should try to fix PPBUS_G3H and then come back to PP3V42


                          • #14
                            I think something is messed up on your PP3v42 line or PPBUS line. I once had one like this where U1900 was causing R7020 to get scorching hot as well and was pulling down PP3v42. This could be a similar situation for you, but start by removing U7090 and injecting 3.42 volts into PP3v42. See if there is any amperage draw.


                            • #15
                              Replace L7095, could have internal short between turns.
                              Also change C7094.


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