820-01987 no boot

[Sr. Robot]

Hi, got an 820-01987 that turned off during use.

CPU gets hot but no image, no Caps Lock light.

U8250 was burned (no corrosion). Was replaced but i get no SENSOR_PWR_EN. Diode mode to ground is 0.750

PP3V3_G3H is 3.3v

 

[2informaticos]

CPU core coils get voltage?

 

[Sr. Robot]

I just noticed that the CPU only gets warm when J6801 is connected.

If J6801 connected i get 0.8v on CPU core coils.

If J6801 is not connected i get:

PPDCIN_G3H: 20.3v

PP3V3_G3H: 3.3v

PPVCC_S0_CPU: 0v

 

[2informaticos]

Really strange, MLB should boot without trackpad connected; but will not load macOS.

 

[Sr. Robot]

With trackpad connected i get 0.65v on SENSOR_PWR_EN.

 

[2informaticos]

Try another U8250.
Be sure to get good solders.

 

[Sr. Robot]

Got another U8250, no change.

Shouldn't U8250 still get SENSOR_PWR_EN even if its bad?

 

[2informaticos]

I wanted to discard U8250 failure; it can pulls down the signal in such case.

Not sure when in the power on sequence this signal comes high.

 

[Sr. Robot]

Got an U8250 from another board of the same model.
Now i got both SENSOR_PWR_EN and PP3V3_S4SW_SNS but still no boot.

Tried DFU but it gives error "AMRestorePerformRestoreModeRestoreWithError failed with error: 9" when installing system

 

[2informaticos]

Which coils get voltage, in normal way?