asus gl703gs detecting short

[prow]

I have this motherboard from the title, there is no schematic or boardview.
When i apply the adapter nothing happens, no lights, only little buzzing noise but adapter is not going to protection mode. Later i check and on first power mosfet there is 19,3 v but later nothing (it is not opening)....Then i check again and every time i apply the adapter it will open the second power mosfet but voltage is just droping...9v...6v...3v...0v
So, i believe the power main controller is closing power mosfets and going to protection mode because ther is a short somewhere in lower power lines?
I checked i believe every coil and most of the current sense resistors and joints but i couldnt find anywhere short to ground.
I have lab power supply and i was thinking to inject voltage/amper but i am not sure how and what? so can anyone help me because i am new in repairs.
So what is obvious is that i will not inject 19volt on second power mosfet because the "protection mode" is activated for a reason and i will probably burn something.
Can someone help me what voltage and amper should i inject and where to to find a short?
Thank you!

[mon2]

Re: asus gl703gs detecting short

Remove the battery (if present). Test again.

Use your lab power supply at 19vdc and set the current limit to 1A. Use it to power the logic board to replace the adapter.

How much current is drawn by your lab power supply?

You can increase the current to match the adapter ratings for this logic board.

You can apply alcohol on the mosfet and local parts. Any misting or quick evaporation of the alcohol when powered? If yes, that part is heating up.

Post clear pix of this area of the logic board. So we can review the mosfet markings, the charger IC.

If the mosfets are being turned on by the charger IC but fail to pass through the adapter voltage, the mosfets may be damaged. Also the charger ic may be in current limit mode based on the ILIM configuration often set by resistor voltage dividers.

[prow]

Re: asus gl703gs detecting short

Hi,
I did remove battery before.
I will try with lab power supply, but as i mentioned when i plug the adapter on first mosfet on drain i have 19,3V. Source is a problem...its dropping 9v, 6v, 3v, 0v....on both power mosfets. To my understanding that means that power main controller is closing source by cutting gate....?
I did replace both mosfets but its the same.

[mon2]

Re: asus gl703gs detecting short

Post the details (pics) of the IC linked to the DCIN mosfets. Then we can perhaps study a reference schematic from datasheets (if public) or another laptop example circuit.

Never mind - found some details. Will post them in a few minutes...

[mon2]

Re: asus gl703gs detecting short

more.

Start with:

1) voltage @ attached locations.

[prow]

Re: asus gl703gs detecting short

1. a/c dock in 19,6 v
2. Ilim 0,1 v. sometimes 0,3v dropping to 0,2v
3. acdet 2,68 v
4. acok 5,92 v

[mon2]

Re: asus gl703gs detecting short

The current limit value is not correct. Pin # 21 must be a higher voltage value as it sets the max current that will be allowed to be supported by this regulator. You presently have close to 0 volts so this IC will be in shutdown mode.

Review the attached and power down:

1) meter in resistance mode, check the resistance for the 2 resistors that create this resistor based voltage divider.

Resistance of PR8913 ?

Resistance of PR8914 ?

2) meter in volts mode, check the voltage on PR8913, pin # 1.

This must go to +3VA.

Post the values.

[prow]

Re: asus gl703gs detecting short

Resistance of PR8913 ? 62 kohm

Resistance of PR8914 ? 44 kohm

PR8913, pin # 1. - 0 vol

[mon2]

Re: asus gl703gs detecting short

Ok.

1) Both resistors are of the wrong value. They should be replaced. It is possible that the resistance values are incorrect as they are in circuit vs. being removed and then measured. You can consider to carefully remove onto one pad and take their measurements again but the parts are very low cost and should be replaced.

Arrow has them and they ship worldwide.

2) The +3VA rail is not working.

3) Voltage on PL8702, pin # 2 ?

4) mosfet gate voltages for the attached test points ?

P_3VADSW_HG_30

P_3VADSW_LG_30

5) Voltage on PL8701, pin # 1 ?