Macbook pro A1278 doesn't turn ON 820-3115-B

[Adogabriel100]

Hi! this is a Macbook pro A1278 MB: 820-3115-B. It came to me from another store with an attend to repair. Now im trying myself to repair this one.

It doesn't turn on and there is no green/orange light either.
Im using mac power cable by-3200.

those are the actual voltajes values and missing lines:

im stuck here with this one here. dont know where to look now. im thinking about SMC (i already change it, dont know if it is ok)

thanks for the help!

PPBUS_G3H = 12.26V
PPBUS_S5_HS_OTHER_ISNS = 12.26V
PP3V42_G3H = 3.47V
PPVRTC_G3H = 3.47v
SMC_BC_ACOK = 3.33V
PP1V2_S5_SMC_VDDC = 1.2V
SMC_ONOFF_L = 3.47V
SMC_RESET_L = 3.44V
SMC_BATLOW_L = 0V
SMC_ADAPTER_EN = 0V
PP3V3_S5 = 0V
PM_SYSRST_L = 0v
PM_RSMRST_L = 0V
PM_PCH_PWROK = 0V
M_RSMRST_L = 0V
PM_PWRBTN_L = 0V
SMC_PM_G2_EN = 0V

PD: i don't have oscilloscope to check the CLK32k.

[mon2]

SMC_BATLOW_L = 0V

Power adapter is under rated to power this unit if LOW = 0 volts. Which one are you using?

[Adogabriel100]

Power adapter is under rated to power this unit if LOW = 0 volts. Which one are you using?

Hey mon2! Im using mac power cable by-3200.

[mon2]

doesn't turn on and there is no green/orange light either.
PPBUS_G3H = 12.26V

SMC fault.

reference:
820 2936-B no green light, PPBUS_G3H 12.29v | Rossmanngroup Forums

PM_PWRBTN_L = 0V

Is your power button stuck? Check this line.

[Adogabriel100]

SMC fault.

reference:
820 2936-B no green light, PPBUS_G3H 12.29v | Rossmanngroup Forums

Of course i thought the same thing, i replace the SMC and it still show the same behavior.

in that post that you re put in as reference. The guy says that he replace the SMC twice and after that the mac has the same behavior. in fact, he take off the SMC and put on another MB and it work normally.

I'm going to look for another SMC and try it again. I'll change it and then I'll tell you how it went.

[mon2]

Do check if the power button line is switching between LOW and HIGH logic levels when you press and release.

[Adogabriel100]

yes, it does the switch between LOW and HIGH logic levels.

I changed the SMC again and it does the same behavior.

[reformatt]

First, there is a typo in the schematic for the SMC. Main power line is PP3V42_G3H, not PP3V3_S5_SMC (which is derived from the PP3V3_S5 supply, controlled by the SMC, so you have a chicken and the egg situation).

With non functional SMC's, you check

1. 3.42V at L4901
2. PP3V3_S5_AVREF_SMC present
3. PP1V2_S5_SMC_VDDC present
4. SMC_RESET_L = 3.3V
5. XTAL cct (Y5010, R5010 etc) is not corroded or tracks missing to SMC.

If the SMC is working, you should at least have SMC_PM_G2_EN go high to enable PP3V3_S5.

[piernov]

First, there is a typo in the schematic for the SMC. Main power line is PP3V42_G3H, not PP3V3_S5_SMC (which is derived from the PP3V3_S5 supply, controlled by the SMC, so you have a chicken and the egg situation).

Not a typo, PP3V3_S5_SMC is aliased to PP3V42_G3H_REG. It's a confusing name nonetheless.

Missing, bad or corroded resistors around SMC can also cause issues, such as the SMC JTAG pull-up resistors or SMC_WAKE_L. And as usual the J5100 debug connector, although it's not common to get corrosion there on MBP, unlike MBA.

[reformatt]

Adobe search had me landing on PP3V3_S5_REG as the alias, but was in fact PP3V3_S5_SMCBATLOW, should look closer (I was doing this to fill in time while I was waiting on creating a Windows 11 installer). Anyways, I know you don't like Adobe.....

[Adogabriel100]

With non functional SMC's, you check

5. XTAL cct (Y5010, R5010 etc) is not corroded or tracks missing to SMC.

Thank you guys reformatt, piernov and mon2 for the help. in fact, the track of the Resistor R5010 (SMC_XTAL) to SMC was missing. Jump wired and for now, everything is working normal. Thanks again!

[dreamflowers09]

great