820-02100 stuck at 5v

[kjchatman1]

3v8_aon_spmu was shorted to ground after a liquid spill and the rail was restored after removing a burned capacitor. The board booted up fine and everything worked until the next day when the display had no backlight. I probed around UP800 and must've shorted something else because now ppdcin is 5v. I'm not familiar with the power sequence of the non-intel boards

 

[2informaticos]

Compare diode mode readings on secondary power rails with good board.

 

[kjchatman1]

i don't have another board to compare readings . pp1v8_s2 is 6 ohms to ground

 

[kjchatman1]

u8100 is shorted. Can these be ordered in the states? I was hoping to get one quickly

 

[2informaticos]

From scrap boards...

 

[kjchatman1]

i've replaced u8100 and the short on 1v8_s2 is gone but i don't know if u8100 is attached correctly. what can i measure to check?

 

[2informaticos]

Check its LDOs...

 

[kjchatman1]

it's attached and ppdcin_aon is still 5v

 

[2informaticos]

Do you have stable LDOs?
Check on slave PMU too.

Is the machine recognized in DFU mode?

 

[kjchatman1]

after reviving with apple configurator i get "DFU state to DFU state. [com.apple.MobileDevice.MobileRestore – 0xFCA (4042)"

 

[2informaticos]

Check for any short on UP800 area.
Try DFU disconnecting internal LCD.

Be sure to connect charger cable before DFU cable.
Also test with both charger and battery connected.
You may need to try restore option too; it will erase SSD!

 

[kjchatman1]

i think i might've shorted the processor. i tested pp1v8_s1_clvr_vddh by injecting 1.8volts. the voltage on the dc supply drops and the amps goes to max but nothing gets visibly warm on the thermal camera