Before you even touch the power button, the Power Supply Unit (PSU) is already talking to the motherboard.
Once all voltages are stable, a Power OK/Good signal is sent. Finally, a Reset signal is released, allowing the CPU to start reading BIOS code. In-Depth Learning Resources
The CMOS battery maintains the real-time clock and BIOS settings, while a crystal oscillator provides a foundational timing frequency. Phase 2: The Trigger (Power Button Press) desktop motherboard power sequence pdf
A (also called Power On Sequence or上电时序) refers to the strict chronological order in which voltage rails are enabled and the corresponding handshake signals that confirm each rail is stable before the next one activates.
The motherboard knows it is safe to proceed. If this signal is missing, the PC will not start. Stage 5: BIOS and SIO Activation Before you even touch the power button, the
A sample power sequence diagram for a desktop motherboard is shown below:
[AC Plugged] │ ▼ +5VSB ──────────► RSMRST# (high) ──► PCH Standby Ready │ ▼ [Power Button Press] ──► PWRBTN# (low) │ ▼ SLP_S3# (high) ──► PS_ON# (low) ──► Main Rails (+12V, +5V, +3.3V) │ ▼ Power Good (P.G.) │ ▼ VTT_CPU ──► VTT_PWRGD ──► VID[0:5] ──► Vcore ──► VRMPWRGD │ ▼ PWROK + VRMPWRGD ──► PLTRST# (high, inactive) │ ▼ CPURST# (high) ──► CPU begins BIOS execution In-Depth Learning Resources The CMOS battery maintains the
The motherboard bios chip is read, and the system initializes. Result: The Southbridge/PCH wakes up. Stage 6: The "Enable" Chain (VRMs and Rails)
This overview provides a fundamental roadmap for repairing desktop motherboards. For in-depth, circuit-level repair, it is recommended to download a Desktop Motherboard Power Sequence PDF or the specific schematics for your motherboard model to follow these signals with a multimeter.
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The complete power-on sequence from a cold start proceeds through the following stages. Most power sequence PDFs will follow this general order, though specific signals may vary by chipset generation and manufacturer.