820-01598 No power, PP1V8_SLPS2R low

This board was liquid damaged but not very badly. Some corrosion around U6903 and PP3V3_G3H_RTC was shorted to ground. I removed U6903 but it was still shorted so I injected voltage and found U7800 was getting hot. I removed U7800 and the short was gone. I replaced both U6903 and U7800 from the same model donor board, and I now get 3.3v on PP3V3_G3H and 12.3v on PPBUS but only about .450v on PP1V8_SLPS2R. I have 0v on the other coils around U7800 also. I assumed the U7800 I got from the donor was bad so I removed it, reballed it, and put it back on the donor board, just to see if I would get 1.8v on PP1V8 and I do get that voltage on the donor, so I don't think this U7800 chip is bad. I have reballed it again and re-soldered it to this board and now back to about .350v-.450v on PP1V8 so something on this board appears to be pulling it down. I do get 20v on this board so idk if that rules out an issue with the CD3217's and T2 or not. Any idea what to check?
 

2informaticos

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Did you compare diode mode reading on 1V8_SLPS2R betwwen the two boards?
Do you get other SLPS2R and AWAKE voltages?

Check LDO rails of U7800.
 
I get .362 in diode mode on that rail on this board, which seems normal and does match a good board. I do not seem to get any other voltages from the PMU.

PP3V3_G3H_RTC - 3.3v
PP3V3_G3H_PMU_VDDMAIN - 0v
PP1V8_SLPS2R - 0.375v
PP1V1_SLPS2R - 0v
PP0V8_SLPS2R - 0v
PP1V2_AWAKE - 0v
PP3V3_AWAKE - 0v
PP1V8_AWAKE - 0v
LDO_CORE - 0v
PMU_LDO3_OUT_R - 0v
LDO_RTC - 0v
PP3V3_S5 - 0v
 
I did not find any shorts on the LDO rails but I found that LDO_CORE was OL when I was checking, which seems to indicate it was not connected to U7800. I removed U7800 again and checked continuity and it looks like the trace is broken. I found a few broken traces to U7800 so I don't think board is fixable unfortunately. Thanks anyway
 
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