820-4924 a1502 ppbus_g3h shorted to ground,but can't find anything hot.

[roy.ruan]

hi guys,

Im having a liquid spilled machine, took it off, not much spilled, little on keyboard connector,and touch pad connector, cleaned them off with ultrasonic, all look fine.

started measuring everything and found that ppbus_g3h is shorted to ground. f7140 pin 1 i have normal around 10-11v, pin2 have 0v.
on pin2 ground resistance is 0. then injected 8v on pin 2,trying touching around for an hour already. nothing hot at all.
not even the CPU.

the thurder port area gets a bit spilled as well,but i checked and all good (not 0 resistance to ground)except the ppbus g3h.really running out of idea here.

btw, i use dc power supply to inject, it's the kind of current looking like a g3hot line is touching the ground without shorted part.
i tried inject the 8v directly to the metal plate on the usb port( ground to ground) gets the same current exactly.....usually if any shorted component, then we get lower than (ground to ground)

really running out of ideas here, please help !

 

[dukefawks]

What sort of current are you running through it? If your PSU is capping at 1 or 2 amps or even shutting down nothing will heat up.

 

[roy.ruan]

PSU limit is 5a. im getting around 3.sth A when i inject around 8v, if i go higher,still getting the same thing

 

[roy.ruan]

halo anyone has ideas or advice?

 

[dukefawks]

3A at 8V is 24W, that must make something hot. I bet it is the CPU. Feel the board with your lips, they are much more sensitive.

 

[roy.ruan]

tried another hour,really nothing at all. only things hot are the jumper wires(i would say they are a bit warm)

 

[dukefawks]

Resistance to GND on PPBUS and L7320?

 

[roy.ruan]

so I found the shorted thing.
previously resistance to GND on PPBUS and L7320 are both 0.004.
I found nothing hot so eliminate the ICs and caps(usually they would be very hot if shorted) I took off the Q7310, that was the shorted thing even that area has no liquid spilled.
I replaced Q7310 and confirm no short on PPBUS already.


so NOW resistance to GND on PPBUS is 0.428 ,on L7320 is 0.005

thought that was it.but Now i connected the charger, PPBUS only gets around 4.0 sth V,obviously not enough.
thought maybe still a short pulling the voltage low, inject 11v again. the current on power supply machine shows 0.01A, normal.........and looking good....
but it's getting only 4.0v, now got confused again..

any idea?

 

[dukefawks]

CPU already had PPBUS voltage to it so good chance it is dead.
For PPBUS check sense resistors around ISL6259, R7121/22/51/52

 

[roy.ruan]

F7140 was blown, replaced it, PPBUS_G3H finally is 11.sth V!

but MFG!still not turning on!! pp3v3 s5 is ready and present already. I think you can be right. maybe the CPU is dead already.
just don't want to believe this shit since spent so much time on it.