220-1101 Question 305
Single answer20+4 pin motherboard connectorA technician is assembling a desktop PC with a modern ATX motherboard. The power supply has a 20+4-pin main power connector, but the technician only plugs in the 20-pin section because it seems to fit the board's socket. When the power button is pressed, case fans spin briefly, but the system does not complete POST. Which action is the BEST next step?
- A
Connect the additional 4-pin section to complete the 24-pin motherboard power connection
- B
Replace the 20+4-pin connector with a 6-pin PCIe power connector from the power supply
- C
Move the 20-pin connector to the CPU power header near the processor socket
- D
Leave the 20-pin connector as installed and disable unused motherboard devices in BIOS
Show answer and explanation
Correct answer: A
Explanation
The 20+4-pin connector exists to support both older 20-pin ATX motherboards and newer 24-pin ATX motherboards. In this scenario, the motherboard is modern and expects the full 24-pin ATX power connection. A partial connection may allow fans or LEDs to activate because some rails are present, but the board may not initialize properly. Best practice is to verify that the full 24-pin ATX main power connector and the separate CPU power connector are both connected securely. This aligns with standard ATX power supply and motherboard installation guidance used by system builders and hardware manufacturers.
- A. Correct.
Correct. A 20+4-pin connector is designed so the detachable 4-pin section can be added to form a full 24-pin ATX main power connector for motherboards that require it. Many modern ATX motherboards expect the full 24-pin connection to provide sufficient power and proper voltage distribution. If only the 20-pin portion is connected, the system may power on partially but fail to POST or behave unpredictably.
- B. Incorrect.
Incorrect. A 6-pin PCIe connector is intended for graphics card power, not for motherboard main power. Although it may appear similar to an inexperienced technician, the pinout, keying, and purpose are different. Using the wrong connector can prevent operation and may risk hardware damage.
- C. Incorrect.
Incorrect. The CPU power header near the processor is typically a 4-pin or 8-pin ATX12V/EPS12V connector, separate from the motherboard's main 24-pin ATX power socket. The 20-pin main connector does not belong there and will not correctly provide CPU power.
- D. Incorrect.
Incorrect. BIOS settings cannot compensate for an incomplete physical motherboard power connection. The issue occurs before normal POST and BIOS configuration can be used. This option reflects the misconception that software or firmware settings can resolve a missing required power lead.