Check for 3.3V on Pin 8 of the BIOS chip. Use an oscilloscope to check for data transmission waveforms on Pin 1 (CS#) and Pin 2 (DO) when the power adapter is first connected. If the EC firmware or BIOS file is corrupted, the system will refuse to transition from standby to the active boot state.
| Symptom | Likely Area | Look for in Schematic | |---------|-------------|------------------------| | No power, no LED | DC-in MOSFETs (PQ201, PQ202) | Page 7 – Charger circuit (BQ24780S) | | 3V/5V missing | PU601 enable signal | Page 11 – EN3V5V from EC | | Short on main power | High-side MOSFET or capacitor | Check B+ rail – page 6 | | No display, backlight OK | LCD_VDD, EDP_HPD | Page 34 – LCD connector pin 5 (EDP_HPD) | | Battery not charging | SMBus lines (SCL/SDA) to BQ24780 | Page 8 – Battery connector pins 3 & 5 | la-d402p schematic