MacBook Air quarter fan spin

[john]

I have this MacBook air 820-00165-02 the PP5V_S5 present
PP5V_S4RS3 getting voltage but is dropping
PP5V_S0 getting voltage but is dropping
PM_SLP_S5_L is getting voltage but its dropping
SMC_S4_WAKESRC_EN 0V
any ideas where to look

 

[2informaticos]

Check for short on every secondary power supply.
Also check after the Power FETs, page58.

 

[arghhh]

Are you sure it's quarter fan spin? These normally spin up and down a few times before they turn on.

Check resistance between pins 17/18 and 27/28 on ISL6259.

 

[dukefawks]

History? Liquid I bet.
Corrosion around U6100? Pin 8 of U1950 corroded?

 

[john]

Yes was water damage. There was corrosion around U6100 that was the place where the water traveled under the board and stopped at u6101 I did replace u6101.
It is quarter fan spin because it's just for one second.
resistance pins 17/18 it's 3.17 ohms and 27/28 28,18 ohms
2informaticos I don't know how to check Power FETs
what are the secondary power supply are they S4? S3?

 

[2informaticos]

Check all resistors on "SPI Bus Series Termination" area...
Pay atention to traces too.
Be sure to correct all the problems on the damaged area first.

 

[john]

nothing in there all looks good

 

[john]

replaced the u6100 and u6101 and the same issue. sometimes the fan is spinning a lite bit sometimes you can hear a noise that is trying to spin the fan but it doesn't have enough power

 

[2informaticos]

"Power FETs, page58"
Do you get voltage at secondary coils?
ALL_SYS_PWRGD?

 

[john]

ALL_SYS_PWRGD I get 3.3V and drops and then I get power and drops again

 

[dukefawks]

CPU Vcore coming on for a second too? Put back original U6100!!! Check all traces from U6100 to all termination resistors again, pretty sure that is where the issue is.

 

[john]

the CPU Vcore is doing the same...I tested all the rails for a short to ground nothing... SPI lines are fine
TP[1]SPI_SMC_CS_L looks bad and TP[1]SPI_MLB_CS_L but they are test points
I noticed something else I did put back the original U6100 and I took u1900 from a donor board now the fan is spinning clockwise for a second and the anti-clockwise for a 1/4 fan spin

 

[dukefawks]

If pin 8 of U1950 looks ok I still say there is an issue with the SPI data lines or termination resistor. You can say they look fine but did you take the effort to actually measure all the resistors and measure continuity between them all?

 

[john]

I measure all SPI Bus Series Termination resistor i checked all the traces with multimeter I don't know what to do I can't find the problem.Is it SPI ROM the problem? Should I rewriting the SPI ROM? Should I check some place else?

 

[dukefawks]

U6100 will be fine. Quarter fan spin can be many things, but in most cases it will be around U6100. Can you take a high-res photo of the U6100 area? Did you check pin 8 of U1950?

 

[john]

No Title

Yes I check and the power is steady at pin 8

 

[dukefawks]

Clearly probe 849 is gone and that could include the via. Is there continuity from U6101 pin 3 to R6117 and R6120

 

[john]

yes there is continuity

 

[dukefawks]

Out of ideas sorry. It must be corrosion somewhere, but cannot see that over the internet.