820-01700 not booting

[Kyle93]

This arrived with no liquid damage but seems to be brain dead. Fans spin but no chime or caps lock light. Screen remains black with no image.

Tried a a DFU restore since data is not needed which completed successfully but no change.

What should be checked next?

 

[Kyle93]

Also disconnected angle sensor to rule out but no change

 

[2informaticos]

What voltages do you get on CPU and GPU coils?

Just in case, check AUX pins of J8500.

 

[Kyle93]

LA950 0.753V
LA870 1.353V
LA860 1.353V
LA850 0.872V
LA750 0.715v
L7231 0V
L7330 1.053V
L7221 0.253V
L7330 1.053V
L7221 0.253V
L7211 0V
L7420 0V
L7410 0V

 

[2informaticos]

L7211/21/31 are tied together (CPU core) and correct voltage should be aprox 0.7V, after 10-15s (when board boots).
It should drop from initial 1.1V aprox.

 

[Kyle93]

L7211 stays at 0v when the board is powered on. No voltage from when the board is first powered on or even after a couple minutes

 

[2informaticos]

"L7221 0.253V"
Are you sure about this?
As I said, L7211/21/31 are tied together...

 

[Kyle93]

I checked again and for a few seconds at times a small amount of voltage will appear but it never goes up to 0.7V

 

[Kyle93]

PP1V8_S5 is 0v

diode is 0.285 but on a good working board diode is 0.345

Should voltage be injected to find the partial short?

 

[2informaticos]

I doubt you can find something injecting voltage.
Too high resistance to heat anything with 2V even.
Possibly bad U7800.
It should be able to deliver 1.8V, as there is no pure short.

 

[Kyle93]

PM_SLP_S3_L also had a partial short so replaced U1200 now have 1.8V PP1V8_S5 along with 3.3v on PM_SLP_S3_L but no changes.

Performed another DFU restore.

L7221 is a steady 0v from when board is powered on