Asus x1404za not charging

[koby058]

Hi

laptop works on charger and works on battery

pu8900 is bq24800

charge circuit Hi mosfet QH8902 was shorted from rain to source , when replaced the new mosfet got shorted immidietly when connecting charger

first and second mosfets are not shorted

When measuring voltage on the charging sense resistor the voltage fluctuate between 10.5 volt to 11.4 volt and after sometime it fixated on 3.42 volt Attached video

here is a boardview for thisasus board

https://www.badcaps.net/filedata/fetch?id=3700551

can you gentleman's help finde the issue?

[mon2]

Remove all power. Meter in resistance mode.

Measure the resistance between SRN & SRP (pins 19 & 20) directly at the charger IC. Testing if the full path resistance matches the reference design from Texas Instruments.

[koby058]

Hi and thanks for your help!

the resistance between 19 an 20 is 20 ohms

[mon2]

Looks good. Share the voltage to ground measurements for:

ACDET ; must be 2v4 or higher to enable the charger function
ACOK ; should be a logic '1' if the adapter is deemed to be ok

on the same charger IC.

[koby058]

ACOK = 6v
ACDET=2.63v

[mon2]

Looks good. Attach only the pre-charged battery pack. Test if you see a voltage on the DCin mosfets. If yes, the DCin mosfets are defective. In this case, the DCin mosfets should be disabled and not allow for a reverse feed to the power adapter. Often, as per article by piernov, the 2nd DCin mosfet leaks.

[koby058]

battery voltage is only on the drain of the second mosfet.
before i had the leak in the second mosfet and i replace it, what else can it be?

[mon2]

Test with a fresh, known good battery. Perhaps the BMS on this battery pack has issues.

[koby058]

what do you think about the voltage fluctuation (in the attached video) in the battery charging circuit?
it happens when no battery is connected

[mon2]

Which video?

[koby058]

attached to the first post

[mon2]

What is the resistance to ground of ACN? Testing if there is a short in the main power rail on the board.

Test the resistance to ground of other inductors on the board.