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Troubleshooting a Samsung S5

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  • Troubleshooting a Samsung S5

    Samsung S5 G900I was a working board!
    (A) DCPS 3.8v applied reverse polarity at the battery terminals
    1. Now permanent 80mA current draw before PTB.
    2. PTB stays at 80mA.
    3. Seated resistance on V_BAT same as known good ok & measuring components downstream from the battery terminals into Max's "charging IC" - normal battery voltages present.
    4. Voltage on the main power rail(VPH_PWR) is 1v with current draw 200mA after injecting 3.8v directly into the main power rail @2Amps max. Seated resistance (diode mode) 0.056 - known good is 0.355.
    5. Probing around the max's charging IC VREG_S4_1P8 (goes to Max's charging IC but also everywhere on the board) Before PTB - voltage on known good 0v, voltage drop on bad 0.479v. Seated resistance is identical to known good.

    Desoldered U7000 (Max's "charging IC" - but seems to do other stuff as well!)
    1a. 70mA before PTB gone now 20mA
    3a. Seated resistance on V_BAT unchanged remains identical to known good
    VPH_PWR behaviour unchanged (still as point 4)
    5a. VREG_S4_1P8 nowbasically the same as known good - 0v drop though seated resistance up to 0.6 from .04- 0.5

    My thoughts…….
    Ok I still have a problem so…. "charging IC" stays off for now. *To me 0.056 seated resistance is a PARTIAL short on the VPH_PWR main power rail and 200mA current draw is not enough to use heat as a troubleshooting tool. Nothing on the board is standing out for a visual clue. I can't see any separate "mosfet" - so I'm pretty sure/convinced that U7000 is(in this case was) responsible for creating VPH_PWR(the main power rail from VBAT). Applying power at reverse polarity definitely killed U7000 but has also caused other problems downstream. From VPH_PWR? Stabbing in the dark I think I need to be troubleshooting a FULL short downstream from VPH_PWR. What do you think?

  • #2
    Vph_pwr is the same as vccmain. Find out what is pulling it down to 1v with a thermal cam. You can find shorts that consume only 0.020A with a thermal cam.


    • #3
      I don't have a thermal Cam. I was thinking to take seated resistance measurements off downstream power rails from VPH_PWR and compare them to known good in the hope of finding a fully shorted line. But this may not be valid ... one of my learning objectives is to understand power rail sequences and the practicalities of troubleshooting them


      • Jessa_the_Professa
        Jessa_the_Professa commented
        Editing a comment
        You already know that you have a short on vph_pwr. Find out why.

    • #4
      Hello Jessa
      Are you planning to get any more seek compact pros and macro lenses into the ipad rehab supply store?


    • #5
      That's great. What about the Seek CompactPro? That's currently showing "sold out".