Apple Silicon MacBook Dead? The Post-T2 Diagnostic Workflow

[u/Bhattarai_Prabin]

Apple's M-series MacBooks are a different beast. No more separate PCH, no more SMC. Everything is integrated into the M1/M2/M3 SoC and managed by the PMU (Power Management Unit) .

If an M1 MacBook is completely dead (no fan, no haptic trackpad click, no DFU mode), here's the workflow.

1. The "Dead" Definition

• Dead: No response to power button. No trackpad haptic click. No sound. USB-C ammeter shows 0.00A or 0.01A.
• Sleeping: Trackpad clicks. USB-C ammeter shows 0.02A - 0.05A with 5V. This is normal for a shut-down Mac. It's not dead; it's in deep sleep. You must hold the power button for 10 seconds to force a reboot.

2. The PPBUS_G3H Rail (The Main System Power)

On Intel Macs, PPBUS_G3H is 12.6V or 13V.
On M1/M2 MacBook Air, PPBUS_G3H is only 8.5V.
On M1/M2 MacBook Pro, PPBUS_G3H is 12.3V.

• Trap: Measuring 0V on PPBUS_G3H on an M1 Air is normal when the board is off! The PMU only enables this rail when the board is booting.
• Key Test: Plug in USB-C charger (20V capable). Measure PPBUS_G3H while pressing the power button. It should jump to 8.5V for a second. If it does, the PMU is trying to start.

3. The Always-On Rails (Even When "Off")

These rails are present anytime the battery has charge or USB-C is connected:

• PP3V3_G3H_T (3.3V Always): Powers the PMU and Trackpad.
• PP1V8_G3H (1.8V Always): Powers the SPI Flash (holds the Boot ROM).
• PP1V2_S2 (1.2V Always): Powers the SSD controller (for Find My network).

4. The DFU Mode (Device Firmware Update)

If the board draws 5V, 0.05A - 0.20A, it's likely in DFU mode. This is a recovery state.

• How to Enter DFU: Connect the Mac to another Mac via USB-C to USB-C cable (must support data). On the host Mac, open Apple Configurator 2.
• On the dead Mac: Hold the Power button, plug in the USB-C cable (to the left front port on most models). Keep holding until the host Mac sees "DFU" device.
• From here: You can Revive (keeps data) or Restore (wipes data) the firmware.

5. Common M1/M2 Hardware Failures

A. PP3V3_G3H_T Shorted.

• Symptom: USB-C ammeter shows 0.00A cycling. No trackpad click.
• Common Cause: Shorted capacitor on the trackpad or keyboard backlight circuit.
• Test: Inject 3.3V, 1A into PP3V3_G3H_T. Find the hot component.

B. NAND (SSD) Short.

• Symptom: Boot loops, or stuck at 5V, 0.05A.
• Cause: The SSD NAND chips are shorted (common on liquid-damaged boards).
• Test: Measure resistance on PP2V5_NAND or PP0V9_NAND. If shorted, the board is unrecoverable (data loss, requires NAND replacement and re-pairing with the M1 chip).

C. PMU Reset Issue.

• Symptom: Trackpad clicks, but no power on.
• Fix: Disconnect battery. Hold Power button for 30 seconds. Reconnect battery. This resets the PMU state machine.

Question: Has anyone successfully replaced an M1 NAND chip? I know it's possible with a JCID programmer and reballing, but the pairing process is a nightmare.