820-3209 green light, no fan spin. ppbus low

[kevinklinkmuller]

the current sensing resisters were toast as well as ISL6259 (short to ground on current sensing pins)
R7005 was also high resistance. replaced all of this and all have the correct values now.

PPbus is on 4.3 volts.
the SMC SCL and SDA lines are both 3.42v

I also replaced Q7080 with no change to PPbus.

I have seen a couple of times that it has gone up to 8.4v but that made no difference. It's not pulsing either

 

[2informaticos]

Check all traces and solders for ISL6259.
Change C7025, just in case.
Check resistance between pins 17/18 and 27/28 directly between chip pins.

 

[kevinklinkmuller]

All good in regards to the traces and solder joints.
Changed C7025 and checked if its turned into a wire but it was fine. However pin 23/27 have direct continuity. i'm guessing this is on purpose

Resistance between 17/18 is 2-3 ohms and on 27/28 it's around 20-25 ohms
so current sensing seems normal?
Feel like this is starting to sound like an SMC issue...

 

[kevinklinkmuller]

would it help if i told you i had a suspicion the battery was bad? can a battery cause ppbus faults like this? such as broken current sensing etc?

 

[kevinklinkmuller]

for whatever reason ISL6259 was again shorted at pins 27/28

 

[kevinklinkmuller]

SOLVED. replaced u7000 again and made sure current sensing circuit has correct resistance. all working.

Moral of the story, just because you replace a part doesn't mean it's not faulty again.

thank you!

 

[2informaticos]

Very true!
I just changed 3 KBCs in a Lenovo board, all new from China.
At least the third one was good...