Can anyone confirm the following info?

[orientalsniper]

Laptop (UX303) is not turning on, there's no 3.3V or 5V.

I'm getting 19V up to Pin5 of PQ8906, I'm getting 0V from Pin 1-4, but there's no short to GND.


Does it mean mosfet PQ8906 (P0A03BEA) failed?

[BlueMidnight]

Re: Can anyone confirm the following info?

The P0A03BEA is an N-Channel FET. To turn on, it requires a higher voltage on the gate (pin 4) than on the source (pins 1-3).

Direct your attention to the circuitry that handles turning the input FETs on and off. Either the input FETs are being turned off intentionally and you need to find out why, or there is a problem somewhere in the circuitry that is connected to the gate (i.e. the charge IC itself or anything else that can affect the voltage on the gate).

[orientalsniper]

Re: Can anyone confirm the following info?

Thanks, I'm gonna check the charger IC PU8901 now (SN2867RUYR).

[piernov]

Re: Can anyone confirm the following info?

Make sure both DC in MOSFET are not shorted. It's common on Asus laptops.

[orientalsniper]

Re: Can anyone confirm the following info?

So far the DC in MOSFET are not shorted, but I traced a very small resistance from PIN1 and PIN2 of charger IC and found a shorted capacitor (PCE8301).

Now I've got another question, I found 2.4 ohms in pin 15 of charger IC (soldered out), the datasheet says it's BATPRES, is this ok? Or do I have another short?

Active low battery present input signal. Low indicates battery present, high indicates battery
absent. The device exits the LEARN function and turns on ACFET/RBFET within 100 µs if BATPRES pin
is pulled high. Upon BATPRES from LOW to HIGH, battery charging and hybrid power boost mode are
disabled. The host can enable charging and hybrid power boost mode by write to REG0x14() and
REG0x15() when BATPRES is HIGH

[BlueMidnight]

Re: Can anyone confirm the following info?

Some boards have a battery presence pin on the battery connector. The corresponding batteries have that pin connected to ground within the battery. When the board sees that signal get pulled to ground, it knows the battery has been connected.

This board does not have a battery presence pin on the battery connector. Instead, it has a 0 ohm resistor (PR6004) connecting that signal permanently to ground. So yes, it should be very close to 0 ohms to ground (plus the resistance of the traces themselves).

[orientalsniper]

Re: Can anyone confirm the following info?

Thank you BlueMidnight for the explanation. Just saw PR6004 is connected to GND.

SEMI-SOLVED!
So I proceeded to replace PCE8301 and soldered back the charger IC and it works. Laptop is fixed!

Short summary:

Found short on PIN 1 and 2 of charger IC, proceeded to connect a 3.3V rail from a PSU and PCE8301 smoked out, proceeded to replace it and it worked.

But battery is not being recognized, does it have anything to do with PR6004 being grounded? Also battery (+) pins (1-3) in motherboard (J6003) is not stable, jumping from 1.9V to 2.0V.

[khaahk]

Re: Can anyone confirm the following info?

Pin 1 and 2 of charger ic are connected via low ohm resistor PR8938, it is used to measure how much current flows. So there should be a low resistance 10mOhms between pin 1 and 2.
Check if PR8938 has gone open line - you might have disconnected the battery via it and that is why you have a different situation.

[orientalsniper]

Re: Can anyone confirm the following info?

Sorry, I meant PIN 1 and 2 had a short to ground. Anyways, customer already took off with laptop and can live without the battery, I suspect the battery was damaged to begin with (6 months unused because of the short).

[oceks]

Re: Can anyone confirm the following info?

thanks so much