Asus X540B dead

[Jane]

Asus X540B has no voltages on the large inductors. I checked 19V rail and the voltage is comming to the first mosfet( to drain) but no voltage on Gate nor on Source. I checked the first and the following mosfet but neither seems to be shorted.
What should be the next step?
Thank you for help

[mon2]

Re: Asus X540B dead

1) link the schematic if available in the schematics forum.

2) which charger IC is onboard? Perhaps the TI BQ series? Need the full details.

[Jane]

Re: Asus X540B dead

Please find enclosed a picture of mainboard.
There is BQ 24780s charging IC. But there is no Vin voltage coming to that IC BQ24780S.
Unfortunatelly I did not find a schematic.
Is it possible ( or good) to bypass 19V to that BQ24780s and test the mainboard?
Or is it risky?
Thank you for reply

[SMDFlea]

Re: Asus X540B dead

Please find enclosed a picture of mainboard.
There is BQ 24780s charging IC. But there is no Vin voltage coming to that IC BQ24780S.
Unfortunatelly I did not find a schematic.
Is it possible ( or good) to bypass 19V to that BQ24780s and test the mainboard?
Or is it risky?
Thank you for reply

If you don`t know what the risks are and what the consequences could be,don`t do it.

.

[mon2]

Re: Asus X540B dead

Post a clear pic of the charger IC area to show the parts.

Vin will be fed by a 3 pin dual diode. Locate it and check the voltage to ground of each pin of this diode.

Likely will be a sot-23 smd package. This part will accept a power feed from the power adapter and also the battery. It will auto select the higher voltage to power the charger IC.

[mcplslg123]

Re: Asus X540B dead

Remove the 2nd mosfet and connect adapter. Do you get 25V at pin4 of 1st mosfet?

[Jane]

Re: Asus X540B dead

@mon2: Please find enclosed a picture of charging IC area. I measured voltages on the
diode marked with red arrow. Is it correct?The path seems to lead to input pin of the charger IC, I think. However, voltages on 3 pins were about 0.03V.
P.S. I also enclosed a picture of input area

@mcplslg123. There is no Vin (input voltage) coming to the charger IC. Do you think there can be any voltage on the pin4 of 1st mosfet( when I remove the 2nd mosfet) if there is no voltage on the charger IC?
I expected the voltage to the 4 pin( Gate) should go from the charger IC.Or am I wrong?

[mon2]

Re: Asus X540B dead

Yes, this dual diode powers the charger IC.

Review the right side trace in the picture which leads to the battery connector. This same trace is broken or was intentionally cut near the end. This trace must be fixed to allow for the battery pack to power the charger IC.

You can use a piece of wire from the same diode pin to the thick trace and scrape off some of the green solder mask, then flux and solder the wire. Or you can do the same with a short piece of exposed wire across the pcb trace itself.

Next, remove all power. Meter in resistance mode. One meter probe to the left diode pin or pcb trace. Be sure you are touching the copper trace and not the green solder mask. Other meter probe to the dcin power connector. You should have continuity leading to the power adapter connector. This is so the power adapter can power the charger IC.

Confirm it.

[Jane]

Re: Asus X540B dead

Thanks a lot for help. The trace was broken.
Now the laptop starts.
Asus logo appears for a second but then laptop turns off.
Do you think it can be LCD problem - short?