asus x401a rev 2.0 locked input voltage 19v

[manh trung]

This x401a mainboard is losing voltage from the adapter 19v when going through pq8801 and pq8802.
voltage levels i measured at ic bq25a

pin 20. 18.7v
pin 5. 2.99v
pin 6. 2.5v
pin 4. 0v

i have replaced many charge controller ic but to no avail. no short circuit detected and 2 open-source mosfets pq8801 and pq8802 also replaced

[mon2]

Re: asus x401a rev 2.0 locked input voltage 19v

Measure the voltage to ground of REGN pin on the charger IC BQ25A.

Also, ACDRV.

What are the measurements?

[manh trung]

Re: asus x401a rev 2.0 locked input voltage 19v

pin 16. 6v
pin 4. 0v

i replaced 4.02k resistor at ACDRV pin, impedance is good but voltage is always 0v
did not detect anything out of the ordinary in the pins. thanks you

[mon2]

Re: asus x401a rev 2.0 locked input voltage 19v

Remove the 4k resistor and measure the voltage again at the ACDRV pin.

[manh trung]

Re: asus x401a rev 2.0 locked input voltage 19v

no voltage

[Sephir0th]

Re: asus x401a rev 2.0 locked input voltage 19v

Pictures of your soldering job please.

[manh trung]

Re: asus x401a rev 2.0 locked input voltage 19v

sorry. Due to daily work, I temporarily put this motherboard on hold. but i want some advice

[mon2]

Re: asus x401a rev 2.0 locked input voltage 19v

When you have quality time, do flux and apply ample heat and low air pressure to make this charger IC swim in the liquid solder. Follow the Louis Rossmann advice, make it 'dance' with a gentle corner nudge with tweezers. The chip will push away and bounce back, naturally onto the PCB pads. Be patient and DO NOT force the push otherwise the PCB pads will be ripped off the PCB.

Once you do this, any short will be removed. The pads will align 'like soldiers'.

Then check ACDRV pin again (without the series resistor). Since you have power to the device AND REGN is ~6 volts, the ACDRV pin should be ~25 volts - unless this IC is defective. Most likely, not soldered properly as noted above by @Sephir0th.

[manh trung]

Re: asus x401a rev 2.0 locked input voltage 19v

Thanks for advices. I will try to report back the results

[manh trung]

Re: asus x401a rev 2.0 locked input voltage 19v

after soldering the pins of the ACDRV ic there was 24v but when I soldered the 4.02k resistor back to the circuit the ACDRV was 0v again. apparently the fault belongs to the 2 mosfets open source 19v from the adapter. it's N channel mosfet with max current 48A and 30v i replaced these 2 mosfet with equivalent but still no result

[mon2]

Re: asus x401a rev 2.0 locked input voltage 19v

Very good.

Remove the 2nd dcin mosfet and power up again.

What is the ACDRV pin voltage to ground?

If ~25v, then remove all power. Meter in resistance mode.

Measure the resistance to ground of the 2nd mosfet pins.

Source (1-2-3) to ground.
Gate (4) to ground.
Drain (5-6-7-8) to ground.

Post each measurement.