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Difficulty: EasyMotherboards Form Factors and Connectors

A technician completes the physical assembly of a new desktop PC, installing the motherboard, CPU, RAM, and power supply. The 24-pin ATX main power and 8-pin CPU power cables are securely connected. However, when pressing the case's external power button, the system shows no signs of life, and the fans do not spin. Which of the following motherboard headers should the technician check first to ensure the physical power button is properly connected?

  1. The front panel system header (PWR_SW)Answer
  2. B
    The 4-pin CPU fan header (CPU_FAN)
  3. C
    The M.2 Key M slot header
  4. D
    The 6+2 pin PCIe auxiliary power connector

Answer

The front panel system header (PWR_SW) should be checked first, as it connects the physical chassis power switch button to the motherboard to initiate power.
The front panel header on the motherboard contains tiny pin blocks dedicated to chassis switches and indicator lights, including the Power Switch (PWR_SW), Reset Switch (RESET), Hard Drive Activity LED (HDD_LED), and Power LED (PWR_LED). If the PWR_SW cable from the chassis is disconnected or incorrectly plugged into adjacent pins, pressing the external power button fails to signal the motherboard to turn on.

Step-by-Step Solution

1
Identify the primary signal component responsible for initiating system power from the case switch.
The case power button connects to the motherboard via small pin jumpers labeled PWR_SW or Power Switch.
When the user presses the chassis power button, it momentarily bridges the two PWR_SW pins on the front panel system header, signaling the power supply to initiate system power delivery.
2
Verify why other motherboard connectors do not handle switch signaling.
Fan headers, storage slots, and graphics card power cables serve cooling, data storage, and direct power delivery functions respectively.
None of those headers connect to the external chassis switch wiring.

Key Concept

Motherboard Front Panel Header Connections
Estimated Time:45s
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Topics

Motherboards Form Factors and Connectors

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