820-00840 ppbus missing

[Yoel Ren]

Hi, so this board came in with board looking clean, customer say this died suddenly, when charger plugged in, I got 20v on dc-in, pp3v3_g3h is present..., and then i see that ppbus is shorted to ground with resistance to ground 0.3 ohm.., I have checked resistance to ground on all big coil
L7410/20/30 = 2.4 ohm
L7210/20 : 4.4 ohm
L7370 : 6.3 ohm
l8060 : 2 ohm
l7900 : 3.9 ohm..
is there any more big coil ? I assume the high side mosfet is not shorted, so all left is caps or cpu ? can I inject voltage to ppbus now ?

 

[2informaticos]

If you don't miss any coil, then is safe to inject voltage.
But, where are L7670/90, L7730, L7960, L8030???

 

[Yoel Ren]

so l7960 has the same resistance to ground with ppbus, so I remove U7960, but ppbus's resistance to ground still same, when i probe for continuity on pin 6 7 8 of u7960 to ground, it is shorted, is it normal ? or the have died ? thanks..

 

[2informaticos]

Do you mean Q7960???

Be sure no solder blob remains between Q7960 pads.
Lift one pin of L7960 and see where the short remains.