820-00840 does not boot when battery is connected

[donnos]

we refurbish this 820-00840 before selling it out to customer, about 2 month later customer complains that it randomly shuts down. 1 week about ~3 times.
we took back the laptop and now it does not boot at all.

Found out that when battery is not plugged in, it boots fine with just charger
Battery + charger = no boot, charger loops after charger hits 20V and goes back to 5V.
Battery only = no boot.

measuring on battery terminal itself i get 0V but if i measure the cells i get 11.8V. Battery lock up, but same case when using known good battery.
when on only battery, ppbus is pulsing about 12v(can't get a good ready from osope) 2 short pulse within 1sec and 2/3 sec of no activity and loops.

Measure current sensing for ISL R7061/R7062 and all is good, measured SMB_SMC_CHGR_SDA and SCL and i get normal communication with SMC(diode reading at 0.395)
not sure what else is wrong here

 

[2informaticos]

Check resistance (ohm scale), over C7020/23.
Also check if Q7065 is not shorted.

What is exact F7000 voltage w/ and w/o battery (charger connected)?

 

[donnos]

C7020 is 2ohms
c7023 is 2ohms
Q7065 not shorted

F7000 with battery + charger = 3+V and dropping
F7000 without battery + charger = 13v

 

[2informaticos]

Check SMC_BMON/DCIN_ISENSE, with both charger and battery connected.
Also try starting in SMC bypass, in same case.

 

[donnos]

okay, was poking around to measure with DMM to measure R5438/39, resister is good. but i noticed R5498 alittle "out of colour"
measure resistance all good. tried measuring voltage, i get 0v. i maybe thought its pulsing and DMM not picking up. i used oscope and touch R5498 pin1. suddenly it boots up. now its working good with only battery

when i unplugged the battery, its dead again

 

[2informaticos]

We need voltage of mentioned signals.
Also check SMC_DCIN/PBUS_VSENSE levels.

 

[donnos]

in terms of resistance they all measure within spec.
SMC_BMON_ISENSE = 500mv pulsing
DCIN_ISENSE = 0v
DCIN_VSENSE = 0v
PBUS_VSENSE = 0v
all measure when charger is + battery plugged in

 

[2informaticos]

Post these signals with charger (not battery) connected only.

 

[donnos]

DCIN_VSENSE = 2.9v
DCIN_ISENSE = 0.2v
SMC_BMON_ISENSE = 1v
PBUS_VSENSE = 2.1v

 

[2informaticos]

Check R7061/62 and their traces.

 

[donnos]

yeap. traces are good to u7000(have tried replacing as well) and to R7060. both resister read 2ohms

 

[2informaticos]

Check both SMC_BMON_ISENSE and CHGR_BMON levels, without battery.
You should get almost 0V there, not 1V.

 

[donnos]

the board has gone from working state to a non-working 20v 450ma now. its a sad sad day
cpuvcore is 0.95v no usb activity