820-02020 a2338 fan full speed all working good

[yair37]

Hi, something very weird: there is no water damage or known damage. The Mac is fully functional (charging fine, boots fine, and all parts are working).
I put the board into a different body and it was the same, the fan immediately goes to full speed when I turn it on.

 

[2informaticos]

Read temperature sensors.
Apple diagnostic shows any error?

 

[yair37]

SMC_FAN_PWM get 1v stable, on a good board is 0v probebly or he get the command to turn full speed fan or bad CPU.. where is the temp sensors? i will check them?

 

[2informaticos]

Use iStats application.

 

[yair37]

the temp are fine.. can i disable the line from the cpu and let it spin just regular spin...?

 

[2informaticos]

"SMC_FAN_PWM get 1v stable"
That is not a DC voltage.
Voltmeter gives you an integrated DC reading according with the width of the pulses.

However the fan can also be controlled by DC voltage there.
You can disconnect SMC_FAN_PWM line from CPU and set a DC voltage, which let fan spins at desired speed.

 

[yair37]

from where i can take DC voltage?

 

[2informaticos]

First of all, it must be from a S0 state; so fan can't spin in suspend mode.

Now looking at fan control circuitry, attacking UE501 with DC voltage is not an option; QE500 works propely with pulses only.
I recommend to check all the components there; post their voltages.