820-3437 Missing v-core

[ALB-Repairs]

No liquid damage, Board is apple refurbished.
Fault is odd, all power rails other than v-core.
ALL_SYS_PWRGD is low.
Fan spins up for maybe 8 seconds, spins down, spins up again and remains on permanently.
Totally lost with this one. Tried SPI rom no changes

 

[aprendiz]

Some rail is pulling down ALL_SYS_PWRGD, even if all voltages are present some PGOOD line is pulling it down......

Remove one by one from R8164, R8165, R8166 and R8168, check ALL_SYS_PWRGD each try untill it goes up, also check Q8150 area...

 

[ALB-Repairs]

Q8150 area was checked, i removed all resistors o ne by one but the rail didn't go back up. Considering that + the fan spinning up and down im almost certain the SMC is bad.

 

[dukefawks]

Why would the SMC be bad. Q8150 is still pulling down ALL_SYS. Look at the diagram and understand how this circuit works. Q8150 needs 4 voltages to come in to release ALL_SYS high.

 

[mainmacman]

Should ALL_SYS on Q8150 be 3.3V ?

 

[ALB-Repairs]

I Was poking it today, didnt really change anything, and then SYS pwrgd came high and so did V-Core, But its still not pulling the correct current, The cpu isnt getting warm. U1950 is good though.

 

[dukefawks]

That is not very helpful. Probably corrosion somewhere.....but it is an Apple refurb board so expect it to be trash.