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ZenBook 13 UX334FL

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Problem Solution
no Power,

19V stops at first inrush

limiter MOSFET (fg. 1)

Diagnosis:
  • measure Vin at the inrush limiter MOSFETS
  • Input area.png
    fg. 1: input area
  • the first MOSFET is not turned on at the gate
  • responsible is this BQ24780s chip
    Bq24780s.png






fg.2:VSYS area (https://www.ti.com/lit/ds/symlink/bq24780s.pdf)

  • here ACDET should be over 2.6V, but is 1.6V
    • so ACOK is not triggered and ACDRV stays 0V
  • the shown short reduces the voltage
  • through voltage injection i found this:
Short area.png






fg. 3 shorted area

  • this cap pulled VSYS down
  • we replaced with 1uF/20V (measured at the other 3 caps, which are the same size