Schematic Top - Lac781p

The fan gave a sudden, sharp spin. On the bench, the HP logo flickered to life. The

[DC Jack: 19.5V] ---> [VIN / DC-IN Section] ---> [Main System Rail: B+ / CLR] │ ┌──────────────────────────────────────────────┴──────────────────────────────────────────────┐ ▼ ▼ ▼ [3.3V / 5V Always Regulator] [RAM Power Regulator] [CPU Core Power / VCore] ├── +3V_ALWAYS (+3VALW) └── +1.35V / +1.2V └── +VCC_CORE / +VDDNB └── +5V_ALWAYS (+5VALW) VIN / Charging Section lac781p schematic top

Before pressing the power button, the system must generate its "Always-On" standby voltages. This is managed by a dual-channel PWM controller (typically a TPS51225 or equivalent). The fan gave a sudden, sharp spin