820-3787-a fan spin and stop loop

[macfix]

Hello

I m working on 820-3787-a board. Its came service for topcase replacemen and workingt but now not turning on. Fan spins then stop loop.


When checked voltages PP5V_S4 enable signal turning on and off, its come from SMC but i cant be sure why SMC defect suddenly. My brain burned any idea for start to check?

PPBUS_G3H = 12.5V and stable
PPVIN_S5_HS_COMPUTING = 12.5V and stable
PPVRTC_G3H = 3.43V and stable
PP5V_S5 = 5V and stable
PP3V3_S5 = 3.3V and stable

 

[dukefawks]

The most likely is of course damage to the board, knocked off component. Long screw damage or something like that.

 

[macfix]

You are definitely right duke but checked under microscope few times but cant find anything. Maybe voltage fallow in schematic can help me find problem
When connected power supply from magsafe connector with connector take 0.23A then 0.01 and again 0.23A loop.

 

[macfix]

Thank you dukefawks after you message checked every connector and found USB line defected and few component missing at I/O board. But when i didnt connect J9500 connector continue same issue.
So question is ; Could be damage U1100 (PCH) from USB data line, and my board problem is could be PCH ? Do you think i have to replace PCH ?

 

[dukefawks]

I doubt it. But the fact that damage was done somewhere makes it likely there is other damage present. There is no systematic solution to this. Any missing resistor can cause this behavior. Inspect better for damage.