u5110 question

[shanenin]

I have been reading and not finding a good answer. Is pin 8 of u5110 an output to the smc or in input from it?

 

[2informaticos]

Pin 8 is 3.3V output for AD/DA converters from SMC.
That is a reference voltage and must be very stable.
If that voltage is not present, usually board can only start in SMC bypass mode.

 

[shanenin]

thank you! what types of things would cause low voltage on that line, is that most often a failing smc?

 

[aprendiz]

Also corroded filtering capacitors on that line....

 

[2informaticos]

U5110 could be bad itself, or even SMC.
But you must start checking the filter caps.
Recently had problems with one Air 820-00165 board.
As it only started in SMC bypass, I waste lot of time checking all sensors output level; all found to be good.
Finally, I remebered that I forgot to check AVREF_SMC presence; such a simply thing.
Once I changed C5125 (found to be shorted), board started properly...

 

[shanenin]

Thanks for taking your valuable time to answer this. It helps me immensely trying to sort stuff out in my head