Liquid Damage - No Power - Possible BB/BB_PMU Problem?
Hey guys. I have an iPhone XR that I am working on that suffers from liquid damage and currently does not power on or charge properly. I have ruled out a parts problem by swapping out the lightning dock charging flex cable and a new battery to no effect. The logic board has been ultrasonic cleaned, as there was visible corrosion on the board.I've taken some measurements and I am leaning on something wrong with BB_PMU or BB itself, but wanted some other opinions. I'll outline everything I've done thus far
Liquid Damage. Visible corrosion in the area around C4191 (PP_VDD_MAIN).
Phone does not power on
Phone attempts to charge at varying ~0.10A
Diagnosis & Repair Attempts So Far:
Ultrasonic cleaned the board due to the corrosion.
Tried new lightning dock flex cable - No effect
Tried new battery - No effect
Found short on PP_VDD_MAIN. Replaced C4191 and short cleared - Still no power or proper charging.
TRISTAR/HYDRA Tester says Hydra is OK.
I have checked a whole bunch of power rails both for voltage and for shorts. I don't THINK I found any shorts (the ones that appear low seem to be alright according to ZXW Tools) , but I did find some rails missing that are tied to BB and BB_PMU. I will post my measurements below.
The first measurement reading on each line is diode mode measurement to ground (red probe on ground, black on rail) and the second measurement is the voltage. Testing was done with the board connected to a DCPS set to 3.8V no screen, battery, or lightning dock connected. A few of them at the end I just got their diode reading and not voltage, but will gladly get those if someone needs to see it.
Various Power Rails:
pp3v0_nand - 0.449 | 2.61V
pp1v8_s2 - 03.15 | 1.8v
pp1v8_always - 0.632 | 1.79V
pp3v3_usb - 0.324 | 3.3
pp_vdd_main - 0.325 | 3.82v
pp_gpu_sram - 0.481 | 0v no screen connected
pp_vdd_boost - 0.393 | 3.76
pp1v1_s2- (short?) 0.095 | 1.069
pp1v2_SOC - 0.538 | 0v
pp_cpu_sram - 0.335 | 0v
pmu_vbatt_vsense- 0.786 | no batt connected
pp1v26_s2- 0.446 | 1.27v
pp0v9_nand - 0.474 | 0v (normal?)
pp_batt_vcc - 0.442 | 3.82v no batt connected
pp_cpu_ecore - 0.443v
pp_cpu_pcore - 0.259PP_SOC_S1 - 0.267
pp3v0_s2 - 0.417pp_gpu - 0.018
And then here are the measurements strictly involving BB/BB_PMU. These are all voltage measurements. The ones that are zero volts, I also took diode measurements and none of the zero volt rails are short:
pp_0v9_SMPS1_BB_SRAM - 0.9V
PP_0V8_SMPS2_BB_DIG - 0V
PP_1V3_SMPS3_XCVR_ANA - 1.24v
PP_0V77_SMPS4_BB_CORE - 0.87v
PP_1V0_SMPS5_XCVR_CORE - 1V
PP_1V85_SMPS6_IO - 1.846v
PP_3V15_LDO1_VFE_AUX - 0V
PP_1V8_LDO2_VFE_LNA - 0V
PP_3V3_LDO3_USB_HS - 3.3
PP_1V8_LDO4_BB_MEM - 0v
PP_1V24_LDO5_USB_SS - 1.25V
So it seems to me that my main problem is likely the BB_PMU IC itself which is U_PMIC_K in ZXWTools or the BB itself which is labeled U_BB_K, but that is just somewhat of an educated guess.I was hoping someone could take a look at what I've measured and help me in the right direction. I don't have either ICs in stock for the iPhone XR so before I ordered some chips needlessly, I wanted some help in making sure I'm on the right track in my thinking. Thanks guys!
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