If any step fails, the motherboard halts. Without a , diagnosing which step failed is nearly impossible.
Finding a reliable for a specific model (e.g., ASUS ROG Maximus, Gigabyte Aorus, MSI Tomahawk) is challenging because manufacturers consider schematics proprietary. However, here are the best sources: desktop motherboard power sequence pdf
Modern desktop motherboards follow the Intel ATX Power Supply Design Guide and the to manage power-on and power-down states. Before troubleshooting signals, you must recognize these fundamental states: If any step fails, the motherboard halts
| Step | Rail Name | Typical Voltage | Generated By | Powered Component | | :--- | :--- | :--- | :--- | :--- | | 1 | VSB (Standby) | 3.3V | ATX Power Supply | Super I/O, PCH, LAN | | 2 | VCCRTC | 3.0V | CMOS Battery | CMOS Memory, RTC | | 3 | +3V_DUAL | 3.3V | Dual MOSFET Switch | USB, PCIe wakeup | | 4 | VCC_DDR | 1.2V - 1.5V | DRAM VRM | RAM Slots | | 5 | VCCIO | 0.95V - 1.05V | IO VRM | Memory Controller I/O | | 6 | VCCSA (System Agent) | 0.85V - 1.05V | SA VRM | PCIe Controller, DMI | | 7 | VCore | 0.7V - 1.4V | CPU VRM | CPU Cores | | 8 | VCCST (PCH) | 1.05V | PCH VRM | Platform Controller Hub | | 9 | VCCPLL | 1.8V | PLL VRM | Clock Generator | However, here are the best sources: Modern desktop
[ +5VSB (Standby Power Ready) ] │ ▼ [ Real-Time Clock (RTC) Circuit & 32.768 KHz Crystal Active ] │ ▼ [ SIO Receives Standby & Asserts RSMRST# (3.3V High) ] │ ▼ [ User Presses Power Button -> PWRBTN# Signal to SIO ] │ ▼ [ SIO forwards PWRBTN# to PCH / Southbridge ] │ ▼ [ PCH drops Sleep Signals to Low -> Releases SLP_S4# & SLP_S3# ] │ ▼ [ SIO asserts PSON# (Low) -> PSU wakes up Main Rails (+12V, +5V, +3.3V) ] │ ▼ [ PSU Stabilizes & Sends ATX_PWROK (High) to Motherboard ] │ ▼ [ VRM generates CPU VCORE -> Sends VR_READY / VRMPWRGD ] │ ▼ [ PCH releases PLTRST# (Platform Reset) -> CPU executes BIOS Post ] Phase A: The Standby Stage (S5 State)