I show the process I take when working with a dead iPhone board. The majority of this video are the steps that will solve 99% of iPhones that will not turn on, so I think it is still worth showing. However, in this case my standard routine did not solve the problem. It is important to have a SOP when working with dead boards and because I ran into this problem, I can add one more thing to check.
In this video I first measure nand power rails for shorts, I measure ram power rails for shorts, I check to make sure boost coil is firmly attached, and I test the rest of the pmic outputs for shorts. I then check some first stage voltages (I will check for 2nd stage voltages only if I am working with a "brain dead" device, which this was not).
Still, I can not get any voltages to turn on besides main, boost, and power button.
I then change the PMIC to see if it is dead, but that does not give me any change.
Finally, I change the crystal oscillator and that allows the PMIC to turn on and for the motherboard to boot up. This really should have been checked earlier but it is the first time I have ever seen an XTAL go bad, so it was not really part of my normal diagnostic.
I learned that the XTAL is the last step needed before the PMIC will turn on and that is valuable info to know.
I almost didn't release this video because I am basically misdiagnosing for 25 minutes straight but ultimately decided that it still had good info within that others might find useful. If you are a tech, I hope you enjoy :)