820 4924 No power

[EJS]

Okay Duke, I have another 820 4924 with no power, put to much to into the last one, ended up no fix. This one was liquid damaged. Shop the brought it in was nice enough to clean it before the brought it over. Their tech did indicate corrosion around SMC. Magsafe lights, 12.59ppbus g3h, s5 rails are present, missing S4, and just like the last board P5VS4_EN is missing. Checked all lines for short, also just like last board resistance is low on CPU VCORE. This time I'm only getting 9.4ohms. To answer your question from the last issuse, I checked resistance on V core off of a donor board, and got around 23ohms.

 

[dukefawks]

First thing to check if power cycling on 5V_S4 with a scope preferably. 9 Ohm is a bit low again Also check the usual, crap under SMC, U1900/50, PPVRTC.

 

[EJS]

5v_s4 0v with Fluke, no scope
PPVRTC 3.338v

u1900
pin1 3.338v
pin2 3.338v
pin3 0v
pin4 .250v
pin5 3.337v
pin6 -.005
pin7 0v
pin8 0v
pin9 0v
pin10 0v
pin11 0v
pin12 .404v
pin13 3.42v
pin14 0v
pin15 0v

u1950
pin1 can't take measurement
pin2 .085v
pin3 0v
pin4 0v
pin5 0v
pin6 0v
pin7 0v
pin8 3.442v

I honestly don't know if those voltages look correct or not, should I pull SMC?

 

[dukefawks]

Try a reflow on the SMC first, not full just flux and some heat to see if it clears the crap under it.

It had liquid so there must be evidence of it, inspect closely.