820-2879 not turning on.

BCN_Techs

Member
Hi,


This board had liquid damage in U6990. First PPBUS was 1V and going down, and also all main rails were bad. So finally i checked that R6905, U6990 and U7600 were bad and i replaced them. Now i get green light on magsafe, ppbus and other rails are stable but it doesnt starts. Trying SMC bypass i get fans spinning but no chime no boot.


In SMC BYPASS all_sys is 0,03V.

ALso Checked u7000 17/18 and 27/28 are ok.


Any idea what else can be checked?
 
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2informaticos

Administrator
Staff member
Board stays on, but no activity starting in SMC bypass mode?
Then you have a SMC sensor issue.

Check first AVREF_SMC voltage.
Next check SMC_DCIN/BATT_ISENSE and SMC_PBUS_VSENSE.
 

BCN_Techs

Member
AVREF_SMC is ok (3.3V)

SMC_DCIN/BATT_ISENSE - nothing (0.05V)


SMC_PBUS_VSENSE - 0 V


Already changed SMC from donor board and same result.
 

BCN_Techs

Member
After SMC replacement when toggle SMC_ONOFF_L machine goes to S0 state ( no fan, no chime no image) and SMC_PBUS_VSENSE now 2.1 in S0 mode.


GPU is getting a little warm. CPU cold
 
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2informaticos

Administrator
Staff member
Any pulse on basic signals, in normal mode?
Trigger SMC_ONOFF_L and check power on sequence.

"Board stays on, but no activity starting in SMC bypass mode?"
???
 

BCN_Techs

Member
Still having problems. Battery is shorting board. It starts without battery and works fine, sometimes even it starts with battery too but usually when i start without battery then connect it fan stops. I already changed ISL and SMC again. PPBUS is 12.60V
 

2informaticos

Administrator
Staff member
Never connect the battery with board already powered from charger!
You can fry the SMC one day...

Check again resistance between pins 17/18 and 27/28 at U7000.
Also monitor CHGR_A/BMON and SMC_DCIN/BATT_ISENSE levels.
 

BCN_Techs

Member
17/18 - 3.3
27/28 - 21


All buttom measerments are done with magsafe and battery connected:


CHGR_A/BMON - 0

SMC_DCIN - 0.6 (is it ok?)

BATT_ISENSE - 0V


"Never connect the battery with board already powered from charger!"

Thanks for that, i tried it many times but never thought that it may cause SMC damage. Something new learnt today:D
 

BCN_Techs

Member
"Also monitor CHGR_A/BMON and SMC_DCIN/BATT_ISENSE levels"

I understand to check voltages on this rails, or you mean resistance?
 

2informaticos

Administrator
Staff member
"voltages on this rails, or you mean resistance?"
Volyage level, of course.

"CHGR_A/BMON - 0"
Cannot be just 0V, if board turns on.
Maybe less than 0.5V, but need exact values.

Did you try known good battery?
 

BCN_Techs

Member
CHRG_AMON - 0.752V
CHRG_BMON - 0.05V


Yes, battery is extracted from working macbook ( i dont even trust new ones i have)
 

BCN_Techs

Member
No, Testing it now has been working from battery and charger, restarting, All ok, but it takes 5 minutes to fail again. Not starting in smc bypass when battery and charger are connected.
 

BCN_Techs

Member
I have board now connected magsafe and battery and it starts randomly without doing anything with board. Then when i unplug charger it stops (not working frome battery).
 

BCN_Techs

Member
It is disconnected when making tests. About battery i tried with ori battery and same.


Another thing is happening. When i left computer charging some time (20-30 minites) after that it starts normally with battery and charger connected . After i disconnect and it still working as long as i have battery connected. BUt it never starts from only battery, magsafe must be plugged.
 
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