820-2915-B missing pp5v_sus & pp3v3_sus

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  • rtimots
    Member
    • Dec 2022
    • 11
    • Latvia
    #1

    820-2915-B missing pp5v_sus & pp3v3_sus

    Hello, I have a weird one today, I have a 820-2915-B board that had some issues, first of all I had pp3v3_s5 1,6v, changing the TPS51980 repaired that and now I have 3.3v, but the board didn't power on at this point, looking more I found that I don't have SUS voltages, first I tried to get 5v sus, PP5V_S5_P5VSUSFET_R- 5,05v and P5VSUS_EN_L - 0v , replacing U7940 fixed that, nov I have P5VSUS_EN_L - 4,94v, since I have vcc for this chip and the enable signal I thought that Q7840 was the problem, I changed it with a known good one, still I don't have pp5v_sus. And now starts the strange part, when I was looking around the board and checking voltages and shorts I checked again pp3v3_s5 by touching probe to r5040 and c7940 and suddenly the board turned on, I was shocked since the side I touched on these components was both pp3v3_s5, I started to investigate and replicate this, and for three times it started this way, I checked if I have voltages on both components and I have them, no shorts any where, replacing these r5040 and c7940 didn't fix this either and it dousing start, and now with changed components I can't replicate it any more. Is this a dead PCB or did I shorted sometime more that just one rail together. does anyone have an idea?
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    • rtimots
      Member
      • Dec 2022
      • 11
      • Latvia
      #2
      Re: 820-2915-B missing pp5v_sus & pp3v3_sus

      Also regarding pp3v3_sus it tase the same thing as 5vsus, I have vcc and en signal but don't have sus voltage

        Comment

        • rtimots
          Member
          • Dec 2022
          • 11
          • Latvia
          #3
          Re: 820-2915-B missing pp5v_sus & pp3v3_sus

          Could someone help with this? Haven't understood this problem till now either...

            Comment

            • rtimots
              Member
              • Dec 2022
              • 11
              • Latvia
              #4
              Re: 820-2915-B missing pp5v_sus & pp3v3_sus

              So today i resolved this issue, when searching web for this problem many people mention to only test with genuine apple 85w power supply, and since i had exactly this i didn't wonder this is the fault, bet then remembered that i changed the wire from Ali express. Since i didn't have another, i used a cinema display with broken screen as the charger and this fixed this issue, so remember that if the wire has been changed it may not register as 85w charger

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