Asus Vivobook F712E, no power, no charging, works only with battery, help!

[Ariu]

Hello, i have a asus notebook, that doesnt power on at all or charge.
it works only with battery plugged in without charger.(no schematic available)

BQ24780S ic already replaced with a good one but same issue, 0V on the source and gate of 1. mosfet.
No short on 1. and 2. mosfet.
i am able to measure only 3.2V on the CSR.

BQ24780S voltages:

1. ACN ->3.2V
2.ACP ->3.2V
3.CMSRC ->0V
4.ACDRV->0V
5.ACOK->0V
6.ACDET->0.66V
24.REGN->6V

when i inject 19.5V on the CSR the notebook doesnt power on.
Does anyone already faced and solved this kind of issue?
Please help.
Thanks

[mon2]

Review the ACDET->0.66V measurement. This is a raw voltage derived from a dual resistor based voltage divider. You should see a high side resistor that will be the adapter voltage (~19v) on one side and another resistor on the low side. The common middle connection between the 2 resistors offer a safe and lower voltage for the ACDET. This voltage must be 2v4 or higher to be considered to be worthy of powering the logic board.

Once this voltage is at least 2v4, the rest of the voltages should kick in.

[Ariu]

Thanks, but i do not understand why ACDET ->0.66V , but when BQ24780S ic is desoldered , ACDET is over 2.4V and that should be right according to voltage devider.

The charger ic itself is fully functional, beceause is from a spare board and the charging circuit was fine.

[mon2]

Measure the resistance of the high and low side of the parts on the ACDET line. Based on the last post, they should be ok but confirm. ACDET is a high impedance input to the charger IC so the voltage level should not be impacted when the charger IC is onboard.

ACOK is not OK but that is most likely due to the ACDET voltage being too low.

Confirm if you have a voltage on the SMBUS SDA / SCL lines. These require an always on +3V rail which may be defective.

Based on the 3v2 voltage on ACN/ACP - the battery is supplying this voltage? What is the voltage of the battery at the battery connector?

[reformatt]

Some Acer/Asus designs have a switch inside the DC Jack which often fails. IIRC, it disables ACDET till that switch is closed. Just a thought.

[Ariu]

All the measurements that i posted in the 1. post are with the charger connected without battery.
no scl or sda voltage on smsbus line.
R1 86k and R2 17k.( i tried also replacing R1 866k and R2 133k from the spare board and i get only 0.25V on ACDET line)
On the battery Connector i have 0.256V , thats fine without the battery connected.

when i inject 2.5V on ACDET pin then 19.5V is passing through the 1. and 2. mosfet.

i also noticed that a capacitor is connected in parallel mode to R2 (low side of ACDET) maybe this is causing this?

[mon2]

Yes, remove that cap. Unable to find schematics for this Asus so you are our eyes and ears on this case. Test again.

[Ariu]

Problem solved. I removed a resistor that was also on that ACDET line but not R1 or R2 and now Notebook is working and charging fine.
i will take later a picture of the removed resistor that caused this strange issue being 0.66V on ACDET line.
Perhaps someone will have same fault in the future.
thanks mon2

[reformatt]

The designs I've encountered have a FET that is biased on normally and pulls the ACDET line down. The gate of that FET is turned off once the switch inside the DC jack is closed and pulls it to ground. Without a schematic hard to know for sure, but DC jack is common failure on Asus and Acer laptops in this respect.

[Ariu]

That resistor was causing the failure pulling low the ACDET line.
i am not sure what value muss have that resistor because no schematic available but the important thing is, Notebook is fully functional without any issues.