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Difficulty: MediumMotherboards Form Factors and Connectors

A technician is assembling a desktop computer and has connected the 24-pin ATX power cable from the power supply unit to the motherboard. When the power button is pressed, the internal LEDs light up and the cooling fans spin, but the system fails to complete POST and provides no power to the processor. Which of the following power connections did the technician most likely omit?

  1. The 4-pin or 8-pin EPS12V / CPU power connector located near the CPU socketAnswer
  2. B
    The 6-pin PCIe auxiliary power cable connected to the mainboard front panel header
  3. C
    The SATA power cable connected directly to the motherboard primary M.2 slot
  4. D
    The secondary 20-pin Molex power connector attached to adjacent DIMM slots

Answer

The 4-pin or 8-pin EPS12V / CPU power connector located near the CPU socket
The correct option is the choice specifying the 4-pin or 8-pin EPS12V connector. Modern motherboards require a separate 4-pin or 8-pin power connection located near the processor socket to power the CPU voltage regulator circuits. Connecting only the 24-pin main ATX power cable provides power to board components and cooling fans, but leaves the processor unpowered, causing POST to fail.

Step-by-Step Solution

1
Analyze the reported system symptoms
System receives baseline power (LEDs and fans turn on via the 24-pin main ATX connection), but CPU does not initialize and POST fails.
The 24-pin ATX connector supplies power to motherboard circuitry, RAM, and PCIe slots, but modern CPUs require a dedicated power source.
2
Identify the missing required motherboard connector
Identify the 4/8-pin EPS12V auxiliary CPU power connector.
The EPS12V (or ATX12V) connector provides dedicated +12V lines specifically for the CPU voltage regulator module (VRM).

Key Concept

Motherboard Power Connectors and CPU Power Requirements
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Topics

Motherboards Form Factors and Connectors

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