MacBook Air M2 (820-02536) – Power Cycling Issue

Model: A2681
Board: 820-02536

Symptom (with charger only and battery/charger):
The device continuously power loops between 5V and 20V (5V → 20V/0.01-0.12A → back to 5V → 20V/0.01-0.12A …).

Measurements:

• PPBUS_AON: 12.26V → 11.97V → 6.6V → 12.26V ... not stable
• PP5V_AON: 5V stable
• PP3V8_AON: 3.8V stable
• PP3V3_AON: 3.3V unstable
• PP1V8_AON: 1.8V unstable
• PP5V_S2: 5.1V unstable
• PP3V3_S2: 3.3V unstable
• PP1V25_S2: 1.25V unstable

Notes:

• U5200 (489900A6) has already been replaced with a known-good part. No change in behavior.
• U5200 current sensoring resistors are fine. (all have 0 ohm)
• DFU mode is possible, when I choose "Repair Device" or "Restore Device" I get "Unexpected device state 'DFU' expected 'RestoreOS' (Probably forced into DFU mode externally)" (Apple Logo is visible for 4-6 seconds) - DFU Error: 4014 (SSD voltage present, battery is good)
• The board had prior liquid damage, was repaired, and worked for approximately 4–6 months before failing again.

Very likely board has been affected by corrosion in time, probably under some BGA chips.

Remove F5200 and check if C5252 voltage is stable.

Without F5200 PPVBAT_AON_CHGR_REG is stable (12.26V)

So main power supply is discarded; resolder F5200 now.
Any fluctuation/spike on CHGR_A/BMON lines?

No fluctuation/spike visible on CHGR_A/BMON lines.

Note: I measured at RD518 (CHGR_AMON) and RD528 (CHGR_BMON).

Diode values:
CHGR_AMON: 0.584
CHGR_BMON: 0.584

Check voltage and diode mode to ground on all buck outputs of U8100 and U7700.

Just in case, replace L8430.

U8100:
- MPMU_BSTLQ_LX: 0.326 / 3.8V
- BUCK0_LX0: 0.091 / 0.6 - 1.0V
- BUCK0_LX1: 0.091 / 0.6 - 1.0V
- BUCK0_LX2: 0.091 / 0.6 - 1.0V
- BUCK0_LX3. 0.091 / 0.6 - 1.0V
- BUCK0_LX4: 0.091 / 0.6 - 1.0V
- BUCK1_LX0: 0.006 / 0V
- BUCK1_LX1: 0.006 / 0V
- BUCK1_LX2: 0.006 / 0V
- BUCK1_LX3: 0.006 / 0V
- BUCK1_LX4: 0.006 / 0V
- BUCK2_LX0: 0.052 / 0.7 - 1.2V
- BUCK2_LX1: 0.051 / 0.7 - 1.2V
- BUCK2_LX2: 0.051 / 0.7 - 1.2V
- BUCK2_LX3: 0.053 / 0.7 - 1.2V
- BUCK2_LX4: 0.051 / 0.7 - 1.2V
- BUCK3_LX: 0.250 / 1.8V
- BUCK4_LX0: 0.039 / 0.9 - 1.6V
- BUCK4_LX1: 0.039 / 0.9 - 1.6V
- BUCK4_LX2: 0.039 / 0.9 - 1.6V
- BUCK7_LX0: 0.253 / 1.0 - 1.5V
- BUCK7_LX1: 0.253 / 1.0 - 1.5V
- BUCK9_LX0: 0.255 / 0.6 - 1.1V
- BUCK9_LX1: 0.255 / 0.6 - 1.1V
- BUCK11_LX0: 0.237 / 1.0V
- BUCK11_LX1: 0.237 / 1.0V
- BUCK13_LX: 0.250 / 1.2V

U7700:
- BUCK5_LX0: 0.250 / 0.7 - 1.1V
- BUCK5_LX1: 0.250 / 0.7 - 1.1V
- BUCK6_LX: 0.391 / 2.6V
- BUCK8_LX0: 0.222 / 0.8 - 1.2V
- BUCK8_LX1: 0.222 / 0.8 - 1.2V
- BUCK8_LX2: 0.222 / 0.8 - 1.2V
- BUCK10_LX: 0.108 / 0.5V
- BUCK12_LX: 0.320 / 0.8 - 1.3V
- BUCK14_LX: 0.411 / 1.1 - 1.8V
- SPMU_BSTLQ_LX: 0.324 / 3.8V
- SPMU_AMUX_AY: 0.589 / 0V
- SPMU_AMUX_BY: 0.589 / 0V

Note:
- It initially rises to 1.0 V (for example BUCK0_LX0), then drops to about 0.6 V. I observed this behavior on all BUCK regulators that have more than one listed voltage level.
- L8430 looks fine and voltage is stable (3.8V), so it should be fine?

Is important voltage on boost side of L8430; which shoudn't be 3.8V...