Do you have a short on VCC_MAIN or not? Are you testing just the logic board or is it fully assembled (display, cameras etc.)?
Water damaged phones can have multiple problems and many times they are unfixable. You have to start at the beginning and do a thorough visual inspection (preferably with magnification) to see what parts of the board are affected by corrosion. If it is localized, focus your energy there otherwise take note of all the problem areas.
Test the main voltage rails (VCC_MAIN, BATT_VCC, PP5V0_USB). If those lines are not shorted, then you move on to the voltage rails created by the PMU/PMIC (U2000).
Now, because you have 1.2V on VCC_MAIN, I suspect that one of the secondary (PMIC) voltage rails is shorted, which draws too much current from the the power source and forcing the voltage down. It would help your troubleshooting if you had an ammeter to see how much current is being drawn.
Thank you for your reply, :-).. I did have a short on vcc main yes as it was completely dead.. after removing the common capacitors that short on vcc main I think i have sorted the short now.. I have ultra sonic the board and there doesn't seem any corrosion left unless under ic's.
Yes I am just testing the board at this point.. when I plug the cable into the lighting dock and test the voltage on a vcc main line it comes back at 1.2v.
So you would recommend turning my attention to pmic rails?
Can I just ask what should vcc main be at about 4v? I could post some pictures of what I have done so far?
Thank you again..