Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

[BremiX]

Hello,

so a client gave me this laptop. There was a short in one of usb ports and U67 turned into black mess. I did replace it.

Now laptop turns on for ~5 seconds and then shuts down. No picture, CPU gets hot and area around RAM slots a bit warm.

And weird part starts here... When I connect power supply there are 19V at first 2 mosfets and around CPU, laptop is taking 0.066-0.070 A, when I push pwr button it jumps to 0.500 A, when laptop shuts down it goes to 0.010 A, then I lower voltage from 19V to ~16V and laptop starts taking power again at 0.070 A.

With adapter it's 19V before pushing power button but afterwards it's 16V and it's not turning on, only when I replug adapter.


Any ideas?

Thank you for your time,

Best Regards,

Raitis

[caspian]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

the increase in current means there is still a short on the board.
So check which voltage rail is shorted.

[BremiX]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

the increase in current means there is still a short on the board.
So check which voltage rail is shorted.

Thank you for your answer. I will post results tomorrow.

[BremiX]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

hmm all voltage rails are present. It's getting warm around PU401 chip. I can't locate short there. Any tips?

[caspian]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

carefully check which component gets hotter than others around PU401.

[BremiX]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

carefully check which component gets hotter than others around PU401.

None of them stand out, they are equally warm.

Losing hope with this board...

[caspian]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

check all pins of the suspected components to discover which pin is shorted to ground.
this is not that difficult.
Unfortunately, laptop board repair usually takes a long time.
So I think laptop board repair is more a hobby than a serious business.
I wonder how to turn it into a serious business.

[BremiX]

Re: Need help with Lenovo G780 QIWG7 LA-7983P rev 1.0

check all pins of the suspected components to discover which pin is shorted to ground.
this is not that difficult.
Unfortunately, laptop board repair usually takes a long time.
So I think laptop board repair is more a hobby than a serious business.
I wonder how to turn it into a serious business.

Okay I found the problem. Chip PU502 ( SY8033BDBC) with hole in it...

PS. not LED.