820-3437

[wirelessplanet]

board was liquid damged around smc area. i have reballed smc and now have orange/green light

i have 3v42 and ppubs.
i am assuming that this is not turning on because all of my 3v3 lines are pulsing. could you help me figure out why 3v3 is pulsing. could this be because the smc is bad? should i replace u8020?

3v3_sus is plusing to 3.3v
3v3_s5 is pulsing to 3.3v
3v3_s0 is pulsing to 3.3v
3v3_s3 is pulsing but not 3.3v, only to around .2v (sorry don't have oscilloscope)
3v3_s4 is pulsing but not 3.3v, only to around .2v (sorry don't have oscilloscope

 

[2informaticos]

AVREF_SMC and SMC_RESET_L are both stable?
Tested the board alone on the desk?
What is exact PPBUS_G3H voltage?

Check voltage and diode mode to ground on all big coils.
I suspect more corrosion on the board.
Inspect U7400, U7501 and U7600 areas.
Pay atention to U1950 and Q8150.

 

[wirelessplanet]

ppbus 8.62v
AVREF_SMC - stable 3.298
SMC_RESET_L - stable 3.383v

board is alone with i/o board flex and fan connected.

checked all the big coils and found a short on L7502. i found the bad cap c7550. was a crack in the middle. surprised that i didn't see it on visual inspection. i now have fan spin.

question for you. why does a short on 5v line cause a fluctuating 3v3?

 

[2informaticos]

SMC detects the short.
It has lot of voltage, current and temp sensors.
Depending which sensor is triggered, SMC can decide to cycle/restart the power on sequence.

 

[wirelessplanet]

ahhh that makes a lot of sense. so basicly its pulsing becasue it was power cycling. so i was barking up the wrong tree. thanks for the assistance. learned something today.