Once VIN is stable, the standby PWM controller activates to create +3VALW (3.3 Volts Always) and +5VALW (5 Volts Always). +3VALW powers the Embedded Controller (EC) and the BIOS IC.
When the board draws 0.00A on a DC bench power supply, the issue lies at the very beginning of the power sequence. la-g121p schematic
Check the current sensing resistor ( PR302 or equivalent) right after the isolation FETs. It should read a stable 19V. If it fluctuates or reads 0V, the charging IC has detected a short circuit and closed the protection gates. 2. Always-On Power Rails (+3VALW / +5VALW) Once VIN is stable, the standby PWM controller
Remember: Always start at the power tree. Check ACDET , REGN , and +3.3V_ALW . If those are present, move to the PMIC enable signals. With the LA-G121P schematic open on a second monitor and a steady hand with your oscilloscope, that "dead" Dell will boot to BIOS in no time. Check the current sensing resistor ( PR302 or
The first few pages usually contain the block diagram. This shows how the CPU connects to the PCH (Platform Controller Hub), the RAM slots, the GPU, and the I/O ports. If you have a dead USB port or no display, the block diagram tells you which controller chip is responsible. 2. The Power Sequence Logic
The LA-G121P is a budget-oriented motherboard typically equipped with low-power Intel processors.
Measure the voltage at the power button pin. It should sit at 3.3V and drop cleanly to 0V when pressed, reflecting the transition on the ON/OFFBTN# pin of the EC. Essential Safety Tips for Component-Level Repair