Asus X541UVK REV2 Charging Issue

[neptunept]

Hello. I was given this laptop to attempt to repair.

At first, there were no signs of life and the MOSFET after DC input was heating up really quick when connecting the charger. This looked like a short, and soon I found a bad cap (PCI9102). This was replaced and there was some improvement: laptop powered on with the charger (no battery) and the charging LED came on in orange.

Now I wanted to put the battery back on, but I get the following results:

1. Laptop powers on fine only with the charger (BIOS reports battery 0%).
2. If the battery has enough charge, laptop powers on fine and BIOS reports what seems to be the correct percentage.
3. If I connect both battery and charger, laptop doesn't power on and does not charge (all LEDs off).
4. If I connect the battery and power on the laptop, I may connect the charger afterwards and the laptop stays on. It just doesn't charge.
5. With the charger on and an empty battery, measuring directly at the battery header shows me around 0.8V.

Any ideas of what may be wrong? Thanks.

[mon2]

Re: Asus X541UVK REV2 Charging Issue

Which charger IC is onboard? Do not have access to my schematics as I am in HK. Waiting for the mobile electronic fair to start.

Review the dcin mosfets. Often the 2nd one will be defective in your case but review the source / drain / gate voltage to ground.

Check the voltage of the acdrv pin. On BQ charger ics which drive n-channel mosfets, the gate should be ~25v.

If it is not, remove the 4K resistor but do not lose it.

Power on again. Is acdrv now ~25v ?

If yes, review the resistance across the 2nd dcin mosfet but with no power. If low resistance, thee add mosfet is defective. It must be replaced.

Btw - this is all from the above charger sticky by @Piernov. A must read thread.

[neptunept]

Re: Asus X541UVK REV2 Charging Issue

Which charger IC is onboard? Do not have access to my schematics as I am in HK. Waiting for the mobile electronic fair to start.

The IC is a BQ24780S. I will do the checks you recommended later today and post the feedback here.

[neptunept]

Re: Asus X541UVK REV2 Charging Issue

Review the dcin mosfets. Often the 2nd one will be defective in your case but review the source / drain / gate voltage to ground.

With charger only, all S/D/G were reading 19V. If I connect the battery, the reading is ~battery voltage.

Check the voltage of the acdrv pin. On BQ charger ics which drive n-channel mosfets, the gate should be ~25v.

If it is not, remove the 4K resistor but do not lose it.

Power on again. Is acdrv now ~25v ?

If yes, review the resistance across the 2nd dcin mosfet but with no power. If low resistance, thee add mosfet is defective. It must be replaced.

ACDRV is 19V when only the charger is plugged, and just 11.42V after connecting the battery. I can't remove the resistor right now, but I think I found something: the first DCIN MOSFET (M3056M) is now shorting between D and S (0.026Ω), while G to D or S shows 322Ω. I believe it went bad after so much overheating from the attempts of the laptop's owner to charge it, and I overlooked it after getting rid of the shorted cap.

[mcplslg123]

Re: Asus X541UVK REV2 Charging Issue

Whenever +19V is shorted,the 1st dc-in mosfet almost always gets partially shorted. have seen this on hundreds of baord. I usually replace the 1st dc-in fet even without measuring whenever 19V rail is shorted.

[neptunept]

Re: Asus X541UVK REV2 Charging Issue

It was only that MOSFET, now everything is normal. Thanks everyone!