Lenovo G40-45 Dead, low voltage on B+ Need help

[abuhamza]

I have a Lenovo G40-45 (nm-a281p) motherboad which is dead. I measure there is only 0.9v in B+ while the Vin is 20v

Please help, where to start troubleshoot the problem, thanks.

[cellphoneyeta]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

Check charging pin

[mcoytzhi27]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

Check voltage sensing on PR and mosfet from dc port..

[abuhamza]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

Check charging pin

Pin 1 and 2 = 20v
Pin 3-5 = 0v

[abuhamza]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

Check voltage sensing on PR and mosfet from dc port..

PQ6 = all pins have 20v
PQ7 = Pin 1-4 has 20v, pin 5-8 has 0.9v

Where to measure voltage sensing? sorry, i'm new in this stuff

[abuhamza]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

And i read from the power sequence, that B+ created from PU401. But there is no PU401 in the schematic that I can find.

So, what created B+, or which component that created B+

[abuhamza]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

And weird thing I just noticed, even after i remove the charger, there is still voltage on B+ for a while and it is dropping from 0.9v to 0v very slowly.

[bumper1]

Re: Lenovo G40-45 Dead, low voltage on B+ Need help

Try replace PQ7, I have got same problem with similar lenovo and this worked in my case.
"B+" is created from "VIN" through PQ6 and PQ7. PU401 uses it to power itself.