820-2915 strange problem, only works with fake charger?

[roy.ruan]

having a strange 820-2915 board here. previously it was fixed for the GPU replacement. and worked and tested.

2 weeks later customer returned and said no power at all. so we checked,
the machine can power on with DC power supplier or fake knock off charger. but not apple genuine charger.

few things
all voltages on board are normal when using fake charger, but it has kind like "da ..da..da..da.." it's kind of like electricity sound, it continues.

if use original charger, ppbus_g3h = 1.9v only . no power on. pp3v42 is normal 3.42v

i replaced the isl 6259. replaced almost all components on the one wire circuit already, but no change at all.


any advice?
thanks

 

[dukefawks]

Bad Q7080 is the first thing to try. Check R7005 too.

 

[roy.ruan]

just replaced q7080 and no change. R7005 trace and resistance checked all good, and again, it works fine with those fake chargers somehow

 

[roy.ruan]

my bad,in fact pp3v42 doesn't present most of the time when using genuine charger. even on F6905 there is only 2v , so saying even the charger is not outputting correct voltage? detected a short?

 

[roy.ruan]

and it works fine with charged battery

 

[dukefawks]

Monitor PPBUS and plug in the charger, does it spike up and then shut down?

 

[roy.ruan]

yes, ppbus actually happened to be normal for a like a second then falls . same as pp3v42

 

[roy.ruan]

yes, ppbus actually happened to be normal for a like a second then falls . same as pp3v42

 

[dukefawks]

Remove PPBUS fuse and see if it still drops.