820-2879-B Power issues

[Try2fix]

Hi all,

I am trying to troubleshoot power issues with this 2010 A1278 MBP with a 820-2879-B board.

It has Green light on, no orange.
voltage at main fuse f6905=17.34v bouncing down to 16.94v
Voltage at pin 5 on u6901 =3.40v
pin 1 on u6901 =3.19v bouncing to =3.26v
pin 4 on u6901=3.33v bouncing to 3.40v

No signs of liquid damage or previous entry.

Any guidance would be greatly appreciated, as I am very new to this and keen to learn.

 

[2informaticos]

MagSafe light goes to orange only when battery is connected and correctly recognized.
Post PPBUS_G3H voltage w/ and w/o battery.

 

[Try2fix]

Hi 2informaticos,

Thanks for the reply

PPBUS_G3H measured at pin 2 on f7040 = 12.55v bouncing down to 7.68v with battery
" " " " " " " " = 12.57v " " " 2.39v w/o battery

 

[JohnB8812]

Are you using the power pads to turn on the board?

 

[2informaticos]

"" " " " " " " " = 12.57v " " " 2.39v w/o battery"
I don't understand...

Post voltage for all pins of U6900/01.
Be sure to have original 60/85W charger.

 

[Try2fix]

Sorry, I'm not sure how to do that.

 

[Try2fix]

Sorry for that typo, should have read 12.39v

Readings for U6900
without bat
pin 1: 3.36v -3.41v
pin 2: 0v
pin 3: 276.2.mv
pin 4: 3.29v - 3.37v
pin 5: 3.37v

With bat
pin 1: 3.33v - 3.41v
pin 2: 0v
pin 3: 156mv
pin 4: 3.32v - 3.37v
pin 5: 3.29 - 3.38v

Readings for U6901
without battery
pin 1: 3.20v - 3.25v
pin 2: 3.20v - 3.25v
pin 3: 0v
pin 4: 3.35v - 3.39v
pin 5: 3.39v - 3.40v

With bat
pin 1: 3.25v - 3.26v
pin 2: 3.12v - 3.14v
pin 3: 0v
pin 4: 3.35v - 3.39v
pin 5: 3.39v - 3.40v

All readings taken using genuine 60w charger

 

[2informaticos]

Post voltage and resistance to ground at SCL/SDA lines of battery bus.
Trigger SMC_ONOFF_L and see how PM_PWRBTN_L reacts.

If machine doesn't start in normal mode, try SMC bypass mode.

Check resistance to ground at 3V42 line (ohm mode); you should get more than 30K.

 

[Try2fix]

Pin 4 =SMBUS_BAT_SCL = 3.39V
Resistance to ground = 19.8K ohm (after meter settled, I'm guessing it was charging a cap)

Pin 6=SMBUS_BAT_SDA = 3.39V
Resistance to ground = 86.0 K ohm (after meter settled again)

Sorry, I don't understand the next part:

??????{Trigger SMC_ONOFF_L and see how PM_PWRBTN_L reacts.

If machine doesn't start in normal mode, try SMC bypass mode.}

Pin 2 on R5070 PP3V42_G3H Resistance to ground = 14.8K ohm

I am very new to this, and this is the first Mac I've tried to diagnose

 

[JohnB8812]

Take your tweezers and short SMC_ONOFF_L to ground to start the board. If it doesn?t work, this likely has a dead MCP and can RIP

 

[2informaticos]

"Trigger SMC_ONOFF_L and see how PM_PWRBTN_L reacts"
Solder a wire to SMC_ONOFF_L (pad 1 of R5014/15 for example) and touch the ground with it.
Is the same as pressing power button.

"try SMC bypass mode"
Press power button (see above), connect MagSafe and maitain pressing 5-10s...

Post SCL/SDA to ground on diode mode; red probe to ground.

Remove power, wait 20s and check again 3V42 to ground, ohm mode there.
Then invert multimeter probes and check the other value.
None should be less than 30K.

 

[Try2fix]

SCL to ground = 0.533V
SDA to ground = 0.532V
3V42 to ground = 14.85K
3V42 to ground probes reversed = 1.40K

Just to make sure I understand the process here, When I'm doing these tests, the board is removed but the fan is connected.
Should the fan spin when the board is starting up?, if not, how do I know if it is trying to start?

 

[JohnB8812]

Yes board only plug in the magsafe should get a light on the charger. Then short the power pads (you can google for them) aka SMC_ONOFF_L to ground with your tweezers, and the fan should spin IF the board is working.

 

[2informaticos]

"3V42 to ground = 14.85K
3V42 to ground probes reversed = 1.40K"
---------------------------------
"None should be less than 30K."
Looks like bad MCP; time wasting...

 

[Try2fix]

What does MCP stand for?
Does this mean that the board is beyond repair?

 

[2informaticos]

MCP is the big Nvidia BGA chipset, old enough...

 

[Try2fix]

Ok, so does this mean it's game over for this board?

 

[2informaticos]

Yeah, RIP...

 

[Try2fix]

Ok. Thank you for all your help and patience.