A1502 not powering on but fan runs at full speed..

My a1502 2014 model logic board is not turning on , but fan is running with full speed , no display, no chime sound, Here is the voltage details.
PPBUS_G3H - 12.75V
PP3V3_S5 - 3.350 V
PP3V42_G3H - 3.42V
PP5_S5_LDO - 5.057V
PP5V_S4 - this rail is not stable , it's coming and going every 2 sec approx. Not sure it is normal behavior or not.

I haven't measured other rails ,

could you someone please give a hint where I should start ...


Staff member
First of all, welcome to the forum!

If fan spins, board turns on.
Not working properly, of course.

Any history available?
Check voltage at all big coils.
I have measured all the inductor values, Unfortunately, I do not know the history of this board, This board was full death,
I have just cleaned the full board and found some corrosion on U8005 (1.05V PCH HSIO Switch), Just applied some solder on it (Attaching some pictures of the board). I don't know why some of these rails are not stable, Or it is something expected?

L7630 - PP1V05_S0_REG - 1.057V
L7310 & L7320 - =PPVCC_S0_CPU_REG - 1.701
L7430 - PPDDR_S3_REG - Not consistent ,coming and going every 2 sec approx
L7520 - PP5V_S3_REG - Not consistent, coming and going every 2 sec approx
L7130 - PPBUS_G3H - 12.59V



Staff member
You didn't mention any fluctuation at L7630 and L7310/20.
This is not possible, if L7430 and L7520 fluctuate.

Is your board 820-3476?

Try to start in SMC bypass, just for test.
Yes just measured again, Now I can see the fluctuation in these rails too, I am new to this forum and MacBook board repair, Could you explain how I can bypass the SMC? and where I can find the board serial number?


Staff member
Check under SSD for board code.

Google could help you too...
Board serial number is 820 -3476-A, I am confused about where should I look for solving this voltage fluctuation. Could you give a clue? While bypassing SMC also I have voltage fluctuation And the fan running in the same sequence as other rails, Probably fan supply voltage also fluctuating. Is It a sensing issue? What are the possibilities?
I don't have an oscilloscope, Measured PLT_RESET_L by using a multimeter I can see a 0.3V is coming and going every second on PLT_RESET_L. This means that there is some pulse is coming, But it is not stable


Staff member
An o-scope is not really needed.
The pulse should appear each time fan spins.
Usually getting higher peak value, not only 0.3V.

Check if all output voltages from pages 59 & 60 try to appear.
If not, check diode mode to ground on that rail.
I have measured page 59 and page 60 ,

PP5V_S5 - 5.027V
PP5V_S4 - Fluctuating

page 59
PP3V3_S5 at C3287 - 3.349V - stable
PP1V5_S0 - Fluctuating
PP1V05_SUS at C7841 - 1.035V stable

page 60
1.5V S0 Audio Switch - fluctuating
3.3V S4 Switch - PP3V3_S4_FET_R - fluctuating
3.3V S3 Switch - PP3V3_S3_FET_R - fluctuating
3.3V S0 Switch - PP3V3_S0_FET - fluctuating
3.3V Sensor Switch - PP3V3_S4SW_SNS_FET_R - Fluctuating
5V S0 Switch - PP5V_S0_FET - Fluctuating
3.3V SSD Switch - at R5580 - PP3V3_S0SW_SSD_FET - Fluctuating
3.3V SUS Switch - PP3V3_SUS_FET_R - 3.348V stable
PP3V3_SUS - No voltage (maybe because R8020 is not equipped ???)
1.05V PCH HSIO Switch - PP1V05_S0SW_PCH_HSIO - Fluctuating
Looking at the microscope I couldn't see corrosion around SMC. Could you please educate me how is your attention went to SMC?
I was under the impression that one of the power rail /power good is failing ---> due to that SMC is shutting down the entire power supply enable signals ---> then SMC trying again with new enable after some time --- > again it's fail due to a bad pgood.

please correct me if I am wrong , I may be wrong , I am a power Electronics designer. Normally when we design power converters , power goods are monitored and controlled this way. Not sure how it is done in MacBooks.

Does anybody has a pre measured impedance of each power rails . So that I can make sure if any of the power rails are bad.


Staff member
If PLT_RESET_L pulses, means power on sequence is completed.
This requires presence of all power good signals.

You cannot see corrosion underneath SMC, just reball it.
To be honest, I am stuck, I couldn't remove the SMC my resolder station is not capable to offer enough heat or airflow (I have even tried with450 degree celsius and full airflow).
I think I should buy a new resolder station for BGA's. I have found Louise is recommending QUICK 861DW. To be honest I don't have that much budget. Is there some other solder station which I can afford for a better price?