Asus N705U no power

[bouny56]

Hello

Sorry for my poor english and my little electronic level
Resolve my first laptop problem with this forum , i have now a second one with classic problem for lot's of you i think
Please can you help me?

model: Asus N705u
Motherboard x705UN

The laptop don't wake up

I put 19v adapter, 19 come to first mosfet ok but nothing out and nothing on the gate

No short circuit after it, no short after the main resistance too , nothing get hot with the thermal camera and 1,5v inject

I try to get the IC charge controler
it's a BQ24790S

Here is the voltage

ACn 0
acp 0
smsrc 0
acdrv 0
acok 6
acdet 2,95
iadp 0

IDCHG 0
PMON 0
PROCHOT 0
SDA 0
SCL 0
CMPIN 0,195
CMPOUT 6

batpres 0
tb_stat 0
batsrc 0,148
batdrv 0
srn 0,148
srp 0,148
ilim 0


gnd 0
LODRV 0
regn 6
btst 5,98
hidrv 0,148
phase 0,148
vcc 18,83

regn resistance 56kohm

I try to understand, if i want the first mosfet open i need 25 or 26v on acdrv yes?

Thank for your help

[bouny56]

Re: Asus N705U no power

Maybe i've find , i think the second mosfet stay open , because i have a beep for continuity with my multimeter , so the ic charge shut the power ?

[mon2]

Re: Asus N705U no power

Hi. Yes, ACDRV should be ~25v to enable the 2*DCin mosfets (N-channel).

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins.

Source (1-2-3) & Drain (5-6-7-8)
Source (1-2-3) & gate (4)
Gate (4) & Drain (5-6-7-8)

Post each measurement and the scale used on the meter. If the resistance is low, the mosfet is defective.

Yes, often the 2nd DCin mosfet gets damaged and needs to be replaced.

Also, locate and remove the ~4k ohm series resistor in ACDRV. Do not lose the resistor.

After removing the resistor, what is the ACDRV voltage on the charger IC? Is it now ~25v ?

[bouny56]

Re: Asus N705U no power

Hello thx for helping me

first mos :
source to drain 10,6m ohm
source to gate 10,9 m ohm
gate to drain : 256k ohm

i search after the 4k ohm resistor don't find it for now

[mon2]

Re: Asus N705U no power

gate to drain : 256k ohm

This is too low of a reading for a good mosfet.

Can you now measure the same pins on the 2nd mosfet?

It is possible that the 2nd mosfet is making the 1st mosfet look defective since they share the GATE pin voltage.

Post each measurement.

Suggestion is to flux and carefully remove the 2nd mosfet (not the first) off the logic board.

Then with NO POWER, measure the resistance between the pins of the first mosfet. Do you now have a higher resistance between gate and drain pins?

What are the topside markings of each of these mosfets?

Attached is a partial schematic of an Asus X705UV logic board - yours may be similar.

[mcplslg123]

Re: Asus N705U no power

2nd dc-in mosfet is shorted.

[bouny56]

Re: Asus N705U no power

Hello

sorry for my late answer

I change the second mosfet and everything work now fine

Thx mon2 and mcplslg123 for help

have a nice day