820-3115 Clicking Sound, Unstable SMC_BC_ACOK

brunomotter

Member
Hello guys. This board came to me with no PPBUS_G3H initially. Turned out to be a shorted cap C7121. Replaced it, board worked again. I put it on UC to clean all the dirt as it had some green points. After UC the board does not turn on anymore. I noticed that SMC_BC_ACOK is a little unstable, varying quickly from 3.1V to 3.4V. Tried replacing U7000 and rebelling SMC, still the same. What else can I check?
 

2informaticos

Administrator
Staff member
We need reference about more important voltages and signals.
Check power on sequence.

BTW, do not use UC to clean an working board.
If no sweep function available, you can cause more damage on the board; search on google for hot spots.
 

brunomotter

Member
I have 12.24V on PPBUS_G3H, expected, as I have oscillating SMC_BC_ACOK. PP3V42_G3H stable 3.42V, no light on the charger. No PP3V3_S5 also. And yes, I'm dumb for cleaning the board, I know it! Banging head on the wall right now... Shouldn't have done it!
 

2informaticos

Administrator
Staff member
You have more problems, not just bad ACOK; SMC doesn't communicate with U7000.
What about SMC_RESET_L?

Did you try another DCIN board.
 

2informaticos

Administrator
Staff member
Post voltage and diode mode to ground at SCL(SDA lines of battery bus.
Keep BIL and battery disconnected.
 

brunomotter

Member
SDA - 0.484 measured on pin 2 of R5280 - 3.464V
SCL - 0.484 measured on pin 2 of R5281 - 3.464V

D6950 removed, cooled down board.
 

brunomotter

Member
I cannot see anything knocked off... Just reballed the SMC again to make sure it was not a solder problem, but still the same! I'm pretty sure it has something to do with SMC_BC_ACOK signal not being stable, as the clicking noise seems to be synced with the voltage oscillation on that line!
 

2informaticos

Administrator
Staff member
SMC_BC_ACOK is not stable because of other problem; it is not the reason.
SMC_RESET_L is steady for sure?
Test with other charger, eventually fake one, or lab PSU with 60W cable.
 

brunomotter

Member
SMC_RESET_L is stable. With bench PSU and magsafe 60w cable SMC_BC_ACOK stabilizes and no clicking sound, but no light on charger and PPBUS_G3H remains low at around 12.2V
 
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