[SOLVED] 820-3435 macbook air, green light , not turns on

[punkieftw]

Hello, i have a macbook air with some liquid damage.. i clean very very well the board but this not turn on anymore.
before the clean, sometimes if i have some good luck this board turn on.

my measures:

PPBUS_G3H @ C3080 8,57v

PPBUS_S5_HS_COMPUTING_ISNS @ R7202 8,57v

PPBUS_S5_HS_OTHER_ISNS @ C7500 8,57v

PPDCIN_G3H_ISOL @ R7110 16,93v

PPDCIN_G3H @ R7110 16,91v

PP3V42_G3H @ C5006 3,39v

PPVRTC_G3H @ C1910 3,39v

PP5V_S5 @ C7505 2,76v

PP5V_S4RS3 @ C4690 0v

PP3V3_S5 @ C3550 0v

SMC_RESET_L @ Pin 5 U5110 3,35v

i see pp5v_s5 too low but i dont know why

 

[TCRScircuit]

PP3V3_S5 @ C3550 0v..... Hmm.... Let's think about that. What component generates your 3v and 5v rails?

 

[TCRScircuit]

Let's look at page 52 of the schematic... Notice the pattern?PP5V_S4RS3 Missing. PP3V3_S5 missing. PP5V_S5 low.. Let's think here... Why would a rail go low? Perhaps the buck controller is screwed up? Perhaps there's a short pulling the line down?

 

[punkieftw]

Let's look at page 52 of the schematic... Notice the pattern?PP5V_S4RS3 Missing. PP3V3_S5 missing. PP5V_S5 low.. Let's think here... Why would a rail go low? Perhaps the buck controller is screwed up? Perhaps there's a short pulling the line down?

What do you mean when you say "the buck controller" ? So, how i do to know if this si a short?

 

[TCRScircuit]

Before going further, Learn how to find a short.

Here is what a buck converter is
https://www.youtube.com/watch?v=B5eWpRFC9Aw&list=PLkVbIsAWN2ltOWmriIdOc5CtiZqUTH7GT&index=11

 

[punkieftw]

Before going further, Learn how to find a short.

Here is what a buck converter is
https://www.youtube.com/watch?v=B5eWpRFC9Aw&list=PLkVbIsAWN2ltOWmriIdOc5CtiZqUTH7GT&index=11

ya i know whats is a buck converter.. so, you suggest to change the Q7560? or U7501?

 

[larossmann]

Before replacing U7501 make sure you are getting 8.5v on pin 23 and 3.42v on pin 12.

If that is the case, then check resistance to ground on PP5V_S5.

If resistance to ground on PP5V_S5 is high enough to not be considered a short circuit to ground, replace U7501.

Do not touch Q7560.

 

[punkieftw]

i Have 8,57v at pin 23 and 3,38v at pin 12 of the U7501.. The measures of the PP5V_S5 at the L4820 in diode mode have 508 and the resistance mode have 472 ohms. always red probe to ground.. trying with the black probe to ground dont have any measure.

 

[larossmann]

Replace U7501.

 

[punkieftw]

Fan spins! Solved, thanks you louis!