Lenovo Z50-70 ACLUA/ACLUB NM-A273 - Power circuit shorted

[Disaxxx]

Hello

Laptop - Lenovo Z50-70
Motherboard: ACLUA/ACLUB NM-A273 Rev:1.0
Vendor: HannStar

I was doing some stuff on it utill I saw low battery notification. I have plugged AC adapter and immediately screen went blank. I thought that I was too late with plugging. However it stopped working after this. No LED.

I have checked the board for short circuits.
I noticed a malfunctioning mosfet - PQ302, so I have desoldered it. I checked its resistance, and it's really broken - R<1Ω
However, pins 5, 6, 7 and 8 are still shorted to ground.

Resistance between battery terminals is quite low - about 550Ω.
I tried injecting 14.4V into battery pins, at about 1A I noticed PQ303 heating.
I suspect battery charge module - PU301.

What should I check next to confirm this or find other reason?

[mcplslg123]

Re: Lenovo Z50-70 ACLUA/ACLUB NM-A273 - Power circuit shorted

Keep PQ302 removed from mainboard. Now remove PR301 and check which side is shorted.Inject 1V on the shorted side and see if anything gets hot. Dont inject more then 1V as you may kill the Onboard PCH+CPU if there is any high side fet shorted.

[Disaxxx]

Re: Lenovo Z50-70 ACLUA/ACLUB NM-A273 - Power circuit shorted

Thank you very much for your reply and tips.
I did as you said.

It seems that whole blue line is shorted to GND.
I tried injecting volume at red arrow, but nothing gets hot at 3A. (Could I increase the current even further?).
Picture for reference (737_ACN leads to PU1208 which is not present in my revision of motherboard)

I have also inspected caps but none looks visibly damaged.

[mcplslg123]

Re: Lenovo Z50-70 ACLUA/ACLUB NM-A273 - Power circuit shorted

Yes, you can increase the current to 5A. Btw, what is the consumption on dc supply when you injected 1V,3A?? Check all coils impedance, if no coil is shorted then high side mosfet is not shorted-so you can even increase the voltage a bit safely. But be sure about your measurements, else cpu will be fried.

[Disaxxx]

Re: Lenovo Z50-70 ACLUA/ACLUB NM-A273 - Power circuit shorted

I have increased the current limit to 4A and noticed that PQ40 started to heat a little bit.
After desoldering PJ708 I was pretty sure that it must be one of the capacitors as pins 5,6,7,8 of PQ40 were shorted to GND.
One of them was a little bit scarred on the side, so I decided to remove it from board.
It turned out that PC100 was shorted.

Thank you for helping me