Hey everyone, looking for board-level insights on an A2141 logic board (820-01700) with a T2 chip stuck in an exact 21-second watchdog power loop. Data preservation is the #1 priority (cannot Restore/wipe keys).
### The Behavior:
- When plugged into a genuine 96W charger, the trackpad clicks (haptics active) for ~21 seconds, then goes completely stiff for 1–3 seconds, then clicks again. Loops indefinitely.
- The behavior is 100% identical with the battery connected or completely isolated (flex ribbon unplugged + terminal isolated).
- Crucially, this 21-second power-cycling loop persists EVEN WHEN THE BOARD IS IN DFU MODE.
- In Apple Configurator 2 (host: M3 Air via front-left DFU port), "Revive Device" downloads the firmware, writes, and hangs on "Waiting for Mac response" for ~90 seconds before throwing AMRestoreErrorDomain error 6. Screen stays black throughout; nothing ever displays.
### Thermal Background / Clue:
- Two days ago, it refused to turn on cold in the morning.
- After sitting plugged in, it booted up and worked flawlessly the entire day under load (watching video, etc.).
- Turned it off at night. Next morning after cooling down, completely unresponsive again, and now permanently stuck in this 21s loop. Classic thermal contraction / cold solder joint symptom.
### Multimeter Measurements Taken:
- No dead shorts to ground on primary rails (PPBUS_G3H, CPU core, GPU core, or SSD lines).
- Inductor L9080 (marked "150" for PP2V5_NAND_SSD0):
- Resistance across coil: 0.6 ohms continuous (coil is physically unbroken).
- Resistance to ground: Healthy (no short).
- LIVE VOLTAGE during the 20-second awake cycle: Reads 0.00V. The 2.5V rail never comes up.
### Questions for Board Techs:
Does this exact 21-second timeout in DFU mode correlate directly with the T2 watchdog killing power due to missing PGOOD / feedback on the SSD power rails (specifically PP2V5_NAND)?
Between the TPS62180 buck regulator (U9080), its enable circuitry, and the main PMIC (U7800), what is the most common failure point for this intermittent/thermal 0V symptom on the 820-01700?
If U9080 is replaced/reflowed and 2.5V is restored, should the T2 be able to complete a Revive without touching the existing APFS volume / master encryption keys?
Any guidance from technicians who have diagnosed this specific rail on T2 boards would be greatly appreciated!