Asus G512LI main board R 2.0 will not power on ?

[ub6ib969]

hi,

any assist will be a great help.

Asus G512LI main board R 2.0 Unit does on power, I suspected power mosfets. However missing power to P_CHG_ACMOS_S_ 20 line. Q8901 does have 19.8V at the source. A/D_DOCK_IN is located at PC8915 (pin1) but missing P_CHG_ACMOS_S_ 20 at pin 2.

I do have schematics and boardview if needed.

[mon2]

Re: Asus G512LI main board R 2.0 will not power on ?

See attached.

The 2*DCin mosfets are N-channel. Each requires the GATE pin # 2 on these parts to be higher than the voltage being passed between source / drain pins.

Often, the gate voltage should be ~25 volts to enable these N-channel mosfets.

The voltage is driven by the ACDRV pin on PU8900 (Charger IC) = adapter voltage + REGN voltage = boosted voltage for gate drive.

As per the sticky article by @Piernov (see above - a must read) - the 2nd DCin mosfet will often become defective and cause the gate voltage to tank.

Start with carefully fluxing and removing resistor @ PR8918. This will isolate the ACDRV pin and the DCin mosfets.

Then power up again. Carefully measure the voltage to ground on the removed PR8918. Interested in the ACDRV pin voltage to ground.

Is it now ~25 volts?

If not, continue to measure the voltage to ground of:

REGN
CMSRC
VCC

on the charger IC.

[ub6ib969]

Re: Asus G512LI main board R 2.0 will not power on ?

See attached.

The 2*DCin mosfets are N-channel. Each requires the GATE pin # 2 on these parts to be higher than the voltage being passed between source / drain pins.

Often, the gate voltage should be ~25 volts to enable these N-channel mosfets.

The voltage is driven by the ACDRV pin on PU8900 (Charger IC) = adapter voltage + REGN voltage = boosted voltage for gate drive.

As per the sticky article by @Piernov (see above - a must read) - the 2nd DCin mosfet will often become defective and cause the gate voltage to tank.

Start with carefully fluxing and removing resistor @ PR8918. This will isolate the ACDRV pin and the DCin mosfets.

Then power up again. Carefully measure the voltage to ground on the removed PR8918. Interested in the ACDRV pin voltage to ground.

Is it now ~25 volts?

If not, continue to measure the voltage to ground of:

REGN
CMSRC
VCC

on the charger IC.

thank you for your help. I removed PR8918.

Pin1 CHG_ACMOS_G_20 0.0v
Pin2 P_CHG_ACDRV_20 0.0V
P_CHG_VCC_R_30 19.3V
P_CHG_VCC_30 17.5V

[mon2]

Re: Asus G512LI main board R 2.0 will not power on ?

P_CHG_VCC_30 17.5V

This is too much of a voltage drop.

Check the resistor @ PR8916 = 4R7. Confirm the resistance value.

Also check the resistance to ground of P_CHG_VCC_30.

No power to the board when checking resistance.

Remove the battery as well to confirm this Vcc voltage. It should be very close to the source adapter voltage.

PC8914 is also a suspect due to this voltage drop.

[ub6ib969]

Re: Asus G512LI main board R 2.0 will not power on ?

This is too much of a voltage drop.

Check the resistor @ PR8916 = 4R7. Confirm the resistance value.

Also check the resistance to ground of P_CHG_VCC_30.

No power to the board when checking resistance.

Remove the battery as well to confirm this Vcc voltage. It should be very close to the source adapter voltage.

PC8914 is also a suspect due to this voltage drop.

resistance mode

PR8916 Value = 0.071-0.080
ground probe on ground, and red probe to test.
P_CHG_VCC_30= .0L
VCC=19.2v
PC8914 =19.2V
pin 1 resistance= 0.584 (red on ground and black on pin 1)

[mon2]

Re: Asus G512LI main board R 2.0 will not power on ?

PR8916 Value = 0.071-0.080

?? Select the lowest resistance scale on your meter. Then test again.

The resistance should be around 5 ohms. In your post, do note the units of measure (ie. ohms, volts, etc.). Otherwise, take a picture of the meter face for a review.

[ub6ib969]

Re: Asus G512LI main board R 2.0 will not power on ?

Sorry it was V not in ohms

[ub6ib969]

Re: Asus G512LI main board R 2.0 will not power on ?

PR8916 = 0.588V on pin 2, pin 1 0.646V in resistance mode ( red probe ground and black probe), once I select the 200ohm range my measurement is 194.4 ohm

[ub6ib969]

Re: Asus G512LI main board R 2.0 will not power on ?

update:
replaced pr8916 = 4R7 with 5ohm however still getting 0.0 V @ CHG_ACMOS_G_20