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I have a 820-00281 board that came in with liquid damage and completely unresponsive. After removing a capacitor that had shorted PPBUS_HS_CPU to ground and replacing all four CD3215, I now get 20V on USB-C but 0A.
PPBUS_G3H: 12.6V
PP3V3_G3H: 3.3V
PP3V3_PMICLDO = 3.3V
PP1V25_PMICVREF = 1.24V...
I replaced U8100 from an identical Air 2020 donor board. However, the situation is unchanged, with rapid voltage fluctuations on all PMU outputs. MPMU_VREF_ADC is still 0V.
Thanks, you're right, I got confused by the "LDO" in the rail name. However, note that the schematic does say that PP1V5_VLDOINT_SPMU is an output.
Here are my complete output voltages for U7700 and U8100:
SPMU:
PP0V72_S2_VDD_LOW: fluctuating 0-0.7V
PP1V2_AWAKE_PLL: fluctuating 0-1.2V...
I'm trying to understand the fluctuating power rail issue. The wildly fluctuating voltages are all buck converter outputs of the PMUs U7700 and U8100. The PMU power input is steady at 3.8V. The LDOs (PP1V5_VLDOINT_MPMU, CAP_PPSPMU_VLDO9, PP1V5_VLDOINT_SPMU) are steady. What tells the PMUs to...
Interesting. I found an error in the board view file. CE903 should be flipped around: on all three boards, ground is on the left, not on the right. Explains the low diode readings.
Actual readings are SPKRAMP_INT_L: 0.32 (good boards: 0.0.33, 0.32)
This 820-02016 board was a test board in a shop and abruptly stopped working during the testing of some bad audio boards. USB-C is at 5V, PPBUS is 12.3V, and PP3V8AON is 3.8V. Many secondary rails are fluctuating between 0 and their expected values, about every 1/2 sec. This includes PP1V25_S2...