Asus G751JY dead

[RandomFTW]

Hi all,
I got a beautiful motherboard disassembled from an Asus G751JY. At the beginning it worked well so, I thought about using it as a desktop assembly.
For this purpose I tried to connect a couple of 3 pin low power fans to the 4 pin fan connectors with some mosfets.
It was working well until it stopped working. After some testing I figured out there was a short in a 3V regulator. I changed the mosfets and now it is gone, but the motherboard still does not work.
I have been testing more voltages and noticed all the regulators are off. Then I checked the SIO power (ITE chip?) and is off too, but I cannot find the main regulator in the boardview. You can find it attached.
I do not think the fans caused the issue but I prefer to tell you just in case they did.
Any help is appreciated,
thanks.

[jasko_jacker]

Re: Asus G751JY dead

I have repair the same model yesterday no sign of live whe power button is pressed, the charger chip is a bq24375 but in my case the ITE was in short (pwm fan signal is connected directly with ite) check it first.

[RandomFTW]

Re: Asus G751JY dead

Hi again,
I have checked both chips and found the following:
-There is no 3VA EC.
-The charger chip may be faulty, as the regulator is giving 2.5V at the mosfets to the right side (PQ8804 and PQ8805).
-As the charger chip gives 2.5V, the gate voltage of the main battery mosfet (PQ8803) is the same, while the source voltage is 2.5V too. The drain voltage is 19.5V.
Looks like the mosfet is not triggering because the Vgs=0V, but I am not sure about the cause. I suppose the charger chip should give something close to 24.5V so Vgs=5V and the mosfet works, but I am not sure about the problem.
Thanks for the reply.

[Techtiger]

Re: Asus G751JY dead

PU8800 CHARGE MANAGE IC what voltage you get in pin 1 2 3 4 5 6 7 16 20

[RandomFTW]

Re: Asus G751JY dead

Hi,
sorry, it is my fault. What I was measuring in the previous post was the battery output, which, of course, should be off as there is no battery connected. Then, I can suppose the charge chip is ok.
I discovered the problem comes from a 3.3V regulator, more specifically the output of PU8100. There is something shorted in the +3VS net.
I have tried injecting 1V 2A to it and there is something hot around the U3301 chip (ethernet controller?), but the chip itself is not shorted. The heat may come from the other side too.
Can it be a shorted capacitor?
Thanks.
EDIT: HDMI chip discarded.

[RandomFTW]

Re: Asus G751JY dead

Hi again,
looks like there is something really hot near the HDMI chip (U4701). I am cheking the capacitors. I tried removing the chip but it is still hot.
Thanks.

[Techtiger]

Re: Asus G751JY dead

Before injecting 1V 2A try to put some zippo fuel in the area getting hot with that easy to find short SMD

[RandomFTW]

Re: Asus G751JY dead

Hi again,
sorry for the late reply, but my laptop decided to break so I had to fix it. It is working fine now.
About the board, I removed the HDMI chip U4701 and looks like the short in +3VS is gone.
There is still a short in +3VA_DSWO, which is the output of the 3V regulator PU8100. However, I tried injecting power in both nets, 1V 2A, and looks like the only thing that gets hot is the chipset U2001.
Is there a way of checking whether it is correctly working or not?
In case it is broken, I do not feel confident enough to replace a chipset, looks like a very delicate part.
Thanks.