ZenBook 13 UX334FL Not turning on, 19V stops at the first inrush MOSFET repair

ZenBook 13 UX334FL Not turning on, 19V stops at the first inrush MOSFET repair
Device	ZenBook 13 UX334FL
Affects part(s)	Motherboard
Needs equipment	Screwdrivers, multimeter, hot air station, soldering iron
Difficulty	◉◉◉◌ Hard
Type	Soldering

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Problem description

Repairing a ZenBook 13 UX334FL that does not turn on, and does not charge. This specific issue is related to the inrush limiting MOSFETs.

Figure 1, input area marked.

Symptoms

• Not turning on
• Not charging

Solution

Diagnostic Steps

• Measure Vin at the inrush limiter MOSFETS (Figure 1)
• The first MOSFET is not turned on at the gate
  • Responsible is this BQ24780s chip (Figure 2)
  • Here ACDET should be over 2.6V, but is 1.6V
  • So ACOK is not triggered and ACDRV stays 0V
  • The shown short in Figure 3 reduces the voltage
    

    Figure 2, Bq24780s circuit marked.

Figure 4, shorted component.

Repair Steps

Replace the shorted capacitor.

• This cap pulled VSYS down
• Replaced with 1uF/20V (measured at the other 3 caps, which are the same size).