820-2936 Fan turn on and off cycling, no orange LED when connected to battery

[protocold]

Seems no liquid damage. But USB-C to magsafe converter were used before it is dead.

where to start?

 

[2informaticos]

Use 60/85W Magsafe 1 charger and post some basic voltages.

 

[protocold]

tried to remove Q7550 and the pin 4 pad seems no short but when replaced another Q7550, the short come back.. is this a short?

 

[2informaticos]

U7400 is bad, if has short to ground at pin 4.

 

[2informaticos]

Short on pin4 of U7400, or Q7550?
If on Q7550, what is ohm value of the short?

 

[protocold]

Q7550 pin 4 is connected to U7400 pin 12, when both are on the board, they seems to be shorted to ground(9 ohm). L7550 = 0V when on power.

with Q7550 removed, the pin 4 solder pad have no short and when measure voltage it pulses.

 

[2informaticos]

CPU coils may have very low resistance to ground as normal.
You can compare eith good board.
I suppose you don't have any short there.

Did you try to start in SMC bypass mode?
Just in case, replace R7402 and check its traces and solder to pin 2/U7400.

 

[protocold]

R7402 is good and its traces and solder to pin 2/U7400 are good too.

SMC bypass mode = fan stay on, USB storage has LED on too.

 

[2informaticos]

What is CPU voltage after 10s?
Did you try more DDR3 memory modules?

If machines stays on in SMC bypass, then you have problems with a SMC sensor.
Check first AVREF_SMC voltage.

 

[protocold]

L7510/20 = 0.9v after 10s. L7550 = 0.44v at that time.

machine did stay on in SMC bypass, PP3V3_S5_AVREF_SMC = 3.3v even when the fan stopped spinning..

 

[2informaticos]

VCORE should drop around 0.75V when board really boots.

In SMC bypass the fan should spin continuosly to max speed.

Take a look at the circuitries from pages 49 & 50.
Your starting problem is related with one I/V sensor.
Check their output voltage in SMC bypass mode.

 

[protocold]

SMC_CPU_VSENSE = 0.65 - 0.95 fluctuate
SMC_CPU_ISENSE =0v
SMC_GFX_VSENSE = bouncing 0 - 0.7v
SMC_GFX_ISENSE = 0v
TP_SMC_P1V5S3_ISENSE = 0.27v
SMC_CPUVCCIO_ISENSE = 0v
TP_SMC_SA_ISENSE = unknown test point location
SMC_DCIN_VSENSE = 2.82v
SMC_DCIN_ISENSE = 2.1v and when lifting multimeter it will shut down

I will measure the rest later today but is anyone of the above look suspicious so far?

 

[protocold]

17/18 = 20 ohm
27/28 = 21.1 ohm

 

[2informaticos]

"17/18 = 20 ohm"
You should get 2 ohm aprox there.

 

[protocold]

Replaced R7052 and it is all good now. Thanks for the help.