: Verify the main "Always-On" rails, typically 3.3V and 5V , which must be present before the laptop can start.
| Fault Symptom | Suspect Component | Test Method | |---------------|-------------------|--------------| | DC-in short (~0Ω to GND) | High-side MOSFET shorted, ceramic capacitor (MLCC) cracked | Inject 1V/2A – thermal camera hot spot | | 3V/5V present but no power on | Faulty EC, corrupted BIOS, PCH clock not running | Check EC_PWRBTN# toggles; flash BIOS | | Powers on but shuts down after 2s | Missing power good (PG) signal, overcurrent trip | Check PG outputs from each VRM | | No display, external works | LVDS/eDP circuit, GPU BGA cracked | Reflow GPU as last resort | | Short on CPU Vcore rail | VRM high-side MOSFET shorted, CPU itself dead | Remove coil and check which side is short | Laptop Chip Level Motherboard Repairing Guide