Asus X512F no Power

[Kambi13]

Hello all, I've got an Asus X512F that wont turn on. 19V are going into the first power mosfet, but at the drain I only get 3.16V. Tested BQ24780S for ACOK and it reads 5.95V. What should I look next?

Best regards

[mon2]

Re: Asus X512F no Power

Review the many threads on the same common fault. Remove all power, meter in resistance mode.

Then measure the resistance across the DCin mosfets.

Often, the second mosfet will leak and cause the common gate voltage to appear low.

The mosfet gate voltage is usually connected to the ACDRV pin of the charger IC but with ~4K ohm series resistor.

Start with locating this resistor and removing it. Then power up again.

What is the voltage now of the ACDRV pin on the charger IC? It should be ~25v if it is ok.

Post all measurements.

[Kambi13]

Re: Asus X512F no Power

First Mosfet:
Drain -> Ground - 101K
Source -> Ground - 15,2K
Gate -> Source - 11,7 Ohms
Gate -> Drain - 121,1K

Second Mosfet:
Drain -> Ground - 16,72M
Source -> Ground - 11,02M
Gate -> Source - 11,6 Ohms
Gate -> Drain - 11,7 Ohms

ACDRV measures 3,16V with or without the 4k resistor

[mon2]

Re: Asus X512F no Power

First Mosfet:
Drain -> Ground - 101K
Source -> Ground - 15,2K
Gate -> Source - 11,7 Ohms
Gate -> Drain - 121,1K

Second Mosfet:
Drain -> Ground - 16,72M
Source -> Ground - 11,02M
Gate -> Source - 11,6 Ohms
Gate -> Drain - 11,7 Ohms

Can you confirm these readings? They are very low.

ACDRV value is not valid to enable these mosfets.

Confirm the voltages to ground in the attachment (proceed with caution to not short any pins). Red probe on the pin to test; black probe to ground.

What are the TOPSIDE markings of each of these DCin mosfets? Do you have donor boards or spare mosfets for testing? Most likely these will be standard 30v N-channel mosfets.

[Kambi13]

Re: Asus X512F no Power

CMSRC - 3,17v
VCC - 18,88v
REGN - 6,01v

Don't have any donor boards at the moment that have this exact mosfets

[mon2]

Re: Asus X512F no Power

With caution, lots of flux + heat + enough air pressure, remove the 2nd DCin mosfet off the logic board. Proceed with care to not remove any SMD pads nor have other tiny parts flying off the PCB. Be patient. Only test if the solder is melted with a gentle nudge of the tweezers at the corner of the part. When it moves with ease, the solder is truly melted. Then lift up the mosfet.

After the mosfet is removed, measure ACDRV again.

Note that CMSRC & ACDRV are of the same value - likely due to a leaking mosfet. VCC & REGN are the valid values for a working charger IC.

The N-channel mosfet is nothing special and can be replaced with others (if required). Attaching the datasheet for the larger one in the picture.

[Kambi13]

Re: Asus X512F no Power

Mosfet out
VCC - 18,88V
ACDRV - 24,11v

So as you said 2nd mosfet is trashed...

[mon2]

Re: Asus X512F no Power

2nd mosfet is trashed...

Agreed. Do you have any logic around that may have a similar looking mosfet?

[Kambi13]

Re: Asus X512F no Power

No I dont have anything that looks alike. Do you know by any chance the value and the make of that mosfet. I can see a lot of these smaller ones spreaded across the board but with different markings

[mon2]

Re: Asus X512F no Power

Can you confirm the 2nd mosfet is the smaller one in your picture? Assuming this to be correct since the current sense resistor follows.

To confirm further, remove all power -> meter in lowest resistance mode.

Check the resistance between pin # 4 of the larger mosfet and pin #4 of the smaller mosfet. One meter probe on one pin; other meter probe on the other gate pin.

What is the resistance? If it is ~0 ohms (assuming it will be) -> then BOTH of these mosfets are N-channel mosfets. Just different physical sizes.

Do you have micrometer for measuring the dimensions? If not, we can take an educate guess. Again, any 30V N-channel mosfet should be suitable but we need to drill on the above details.

From where do you buy parts? Digikey ? Mouser ? Aliexpress (will take longer).

[Kambi13]

Re: Asus X512F no Power

Let me solder it back in. I do have a micrometer but it's at home ��, I'll see if I can measure it

[Kambi13]

Re: Asus X512F no Power

Yes it reads 0 ohms. It measures 3x3mm
I usually get from digikey or mouser, but I might be lucky locally

[Kambi13]

Re: Asus X512F no Power

Would this one do the trick?

[mon2]

Re: Asus X512F no Power

Yes - it looks like a fit @ 3*3. N-channel. The Id current may be a tad lower than others @10A but if you have it available, consider to test with this part. Monitor the heat from this replacement mosfet.

Confirm that you are working with a 3*3mm PCB footprint but looks to be correct.

[Kambi13]

Re: Asus X512F no Power

Ok, as soon as I can get my hands on one I'll let you know the results, Thank you so much for your help

[mon2]

Re: Asus X512F no Power

No worries. If you do not have it already but ok to order some, then review Mouser (DK has nothing available on this size).

Here is a list from Mouser:

https://cdn.badcaps-static.com/pdfs/...cd76bdb192.pdf
* high current support

https://cdn.badcaps-static.com/pdfs/...2c5f98db77.pdf
* backup suggestion

Each is 3*3mm - do confirm this with a ruler before ordering. There is of course Aliexpress but they will take longer to source (mosfet joke (SMDFlea is laughing for sure)).

Do update this thread for future readers but suspecting you will be ok after this repair.

BTW: Details of this repair from the 'School of @Piernov' (sticky above).

update - in comparing notes with other Asus laptop schematics, they like to use the QM3016M3 which is a 3*3mm N-channel mosfet.

Datasheet is attached. If you are sourcing from Aliexpress - consider this part number as a fit.

[Kambi13]

Re: Asus X512F no Power

Ok, thank you again, rest assured I will post an update once I get the part.

Best Regards

[Kambi13]

Re: Asus X512F no Power

Update, I got my hands on a replacement mosfet and hold and behold it's working. Thank you so much for your kind help mon2