820-2879 not turning on.

[BCN_Techs]

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?

 

[2informaticos]

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]

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]

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

 

[2informaticos]

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]

Solved. When was working U7600 area i put fuse instead of ressistance R7601

 

[BCN_Techs]

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

 

[BCN_Techs]

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

 

[2informaticos]

"SMC_DCIN - 0.6"
What is that???
Please post correct signal names...

 

[BCN_Techs]

Smc_dcin_isense - 0.6v

 

[BCN_Techs]

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

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

 

[2informaticos]

"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]

CHRG_AMON - 0.752V
CHRG_BMON - 0.05V


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

 

[2informaticos]

Board turns on with both charger and battery connected, in SMC bypass mode?

 

[BCN_Techs]

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]

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]

and now it is working from battery for 1 minute and stop. This board will make me go crazy.

 

[2informaticos]

Disconnect BIL connector when test with battery.
Also try another (original) battery.

 

[BCN_Techs]

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.