Asus Ux303UB, Battery not detected after mb change

[lordalex]

Hello Guys,

my asus laptop ux303ub stoppped working. I guess the mainboard had a cap / mosfet problem, but i couldnt fix it. It stopped to charge and no power with cable or battery.

So i got a spare board from a UX303LNB, which was working, but the battery connector was gone.

I bought it, soldered the connector from my board in and installed win10 again.

so far so good, but the laptop isnt recognizing my battery correct. It stays on, but doesnt show a percentage or something and laptop gets very slow without ac plug.

I cant boot the laptop via battery. if i plug the cable in, i can boot and if i remove the cable, the laptop stays on.


The battery connector has 8 pins. 3 Red, 3 GND. all conneted right.
yellow and white. The pads were gone on the spare board, but i could reconnect them to the little ic next to it with the help of the schematics i found here. So i think this isnt the problem.


what else could be wrong? Some charging ic? Is there an ic at the battery that is faulty?

[mon2]

Re: Asus Ux303UB, Battery not detected after mb change

Hi.

1) yes, the laptop has a charger IC that is controlling multiple mosfets (think of as solid state relays).

2 of such mosfets are linked to the AC adapter in and used to power the logic board.

Then another 1 of the mosfets is used to connect the battery to the same logic board main power rail.

More details in how this works is posted above with a sticky from @Piernov. A must read.

2) in the posted repair guide for this model on this forum, focus in sheet #2 - the very top graphic.

This is the charger ic.

On the left are the 2 mosfets that connect the power adapter to power the logic board using the AC_BAT_SYS rail.

Remove the battery.

Attach the power adapter. Meter in DC volts (30V or higher scale).

Measure the voltage on each pin of the first mosfet.

Every mosfet has source, drain, gate pins. Post the full markings of each mosfet. The repair guide is blurry to read (or my eyes are weak).

Often each mosfet is 8 pin with 4 pins on each side.

Usually, pins 1-2-3 = source. Gate = pin 4. Drain = 5-6-7-8.

Then we can find datasheets for each mosfet. The datasheet will show the location of each pin with pin numbers.

Source = adapter input. Drain = should be the same as adapter voltage. Gate voltage is expected to be HIGHER than adapter voltage by ~+6v. So around 24 to 25 volts on pin #4 of each mosfet. Confirm it.

Both mosfets should be ON to create AC_BAT_SYS.

Post each voltage measurement.

Next, remove all power. Attach the battery (only).

What is the voltage on the battery? Is the battery known to be good?

This battery will be mated to another mosfet. See the graphic in the repair guide.

What is the part number of the mosfet?

What are the voltage readings of each pin on the battery mosfet?

Again, this battery mosfet will connect to the same target AC_BAT_SYS rail to power the logic board.

Very likely you have defective mosfets. They are very inexpensive to source.

Near these mosfets will be charger IC. What are the full markings on this IC ?

Post all measurements to move forward. Will review again after some beauty rest.

[lordalex]

Re: Asus Ux303UB, Battery not detected after mb change

okay, ill test it tomorrow. im at work right now

Will laptop start with battery even if data/clk (yellow and white) are not connected right? it was my first guess, since the pads were missing and i just connected them to the right pins of the ic, the pin was going to.

[mon2]

Re: Asus Ux303UB, Battery not detected after mb change

The I2C pins on the battery are used to communicate with the BMS (battery management system).

The BMS reports the details of the battery pack such as charge cycles of the battery; serial number; etc.

Do measure also the voltage on the I2C lines so we can confirm these pins are not stuck.

If they are stuck, the charger ic may just turn OFF the battery mosfet.

You may have the I2C lines reversed (SCL and SDA) which will not cause any damage but will not allow the charger to communicate with the battery pack.

Post the details.

[lordalex]

Re: Asus Ux303UB, Battery not detected after mb change

Thanks for your help so far!

i attached the battery and measured the pins at the connector and the ic

measurements i get just with battery:

connector:

Vpin: 11,5v
Dat_Clk: 3.25v
Dat_Bat:0.1v

Mosfet near battery connector:
Source: 11.5
Gate: 17.3
Drain: 11.6

if i connect the ac with battery still connected i get following readings:

Vpin: 11,5v
Dat_Clk: 3.25v
Dat_Bat:0.1v

Mosfet near battery connector:
Source: 11.5
Gate: 11.58
Drain: 19.35

[mon2]

Re: Asus Ux303UB, Battery not detected after mb change

Vpin: 11,5v
Dat_Clk: 3.25v
Dat_Bat:0.1v

To confirm, the last line is the I2C DAT signal ? This is not a good value and have seen this fault before. Both lines of the I2C interface should be ~3v3 which means the line is OPEN and is being pulled up by local pull-up resistors.

Remove the battery -> check the voltage of this line again. Still same low voltage?

If yes, it is very possible that the ESD diodes (often 3 legged part) is damaged -> they are dirt cheap. Locate near the battery connector for a 3 legged part (2 legs on one side; 1 leg on the opposite side).

Take some clear pics and post them here.

This part is likely damaged and should be removed off the board to restore the I2C lines back to the normal and expected ~3v3.

The same damaged lines can cause your battery to be not detected.

[lordalex]

Re: Asus Ux303UB, Battery not detected after mb change

Yes, its the data line from the battery connector.

I removed the battery and measured again with only the ac plug.

Clk gives me again 3.3. data went to 1.3

Do you mean this little part, marked in orange?

[mon2]

Re: Asus Ux303UB, Battery not detected after mb change

Yes, that could be the one.

Using the same meter setting -> check the voltage on each of the pins on the side with 2-pins. If this is the correct part, then one side will be 3v3 = SCL pin.

The other pin on the same side will be the low voltage = 1v3 or whatever.

Once it is confirmed, remove this part off the board -> apply flux and hot air and use tweezers to remove it.

Then check the voltage again on the pads on the logic board at this location.

If ok for both pins and ~3v3 for each -> attach the battery and test again.

[lordalex]

Re: Asus Ux303UB, Battery not detected after mb change

ok, i guess its not the right part,

this one measures 5v on the left side of the pin. rest is 0.xx
picture 1

i found this part here. It has 3.3v on each side, but i dont know if it belongs to the battery.
picture 2

what im wondering is, that i cant find another SMB0_DAT and SMB0_CLK besides on this litte ic next to the battery
picture 3

EDIT
omg i made it!

i found out, that SMB0_DAT wasnt routing to the ic on the other side, while SMB0_CLK was. took a wire and connected from battery to other side of the board and it started with battery!

thank you so much for you help anyway. guess i couldnt find a solution without you