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S5 main power rail short mystery

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  • S5 main power rail short mystery

    Samsung Galaxy S5 G900I phone was working fine eg boots fine and everything works except did not connect calls. Since call connectivity issues can be problematic to diagnose and I am focusing on basic repair skills only I instead decided to use this board as a 'guinea pig'. (NB no customer phones were used in this experiment!) So I desoldered the working PMIC, reballed and put back on..... and with that a short appeared on the VPH_PWR - the main power rail. Convinced there must be bridged shorted balls underneath PMIC I desoldered but no shorts and short disappeared after I removed PMIC. Solder on another PMIC - short reappears - no bridging balls. Remove PMIC, short disappears. Take the original PMIC that came from this board and solder it onto another board, no short, - phone boots, everything working fine - no problems. WTF. Have I missed something?

  • #2
    "short disappeared after I removed PMIC" How did you determine this?

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    • #3
      Multimeter Continuity test mode checked a cap on the main power rail when PMIC was on - it tested short. I retested the same cap with PMIC off - tested open

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      • #4
        Signature of a short on the main power rail of Samsung S5 = 50mA before prompt to boot. Also, When I remove PMIC this 50mA before prompt to boot disappears. Instant current draw when injecting through the main power rail also disappears

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        • #5
          Main shorts in Samsungs are different than iPhones. We definitely don't want to be measuring by "beep" We need numbers. A lot of PMIC outputs in samsungs will have low resistance to ground and always beep. For example, if the normal resistance is 100ohms, some boards will "beep" and some will not. This could be at play.

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