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220-1201 Practice Question: Building a new gaming PC and have installed a…
You are building a new gaming PC and have installed a 750W 80+ Gold power supply. After connecting all components, the system powers on for a second then immediately shuts down. What is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A motherboard standoff is shorting the board to the case
A short circuit triggers the PSU's overcurrent protection, causing immediate shutdown. This is common if a motherboard standoff is missing or a screw is lodged under the board. Other causes like insufficient wattage or loose cables typically cause instability, not instant shutdown.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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The power supply is underpowered for the components
Why it's wrong here
An underpowered power supply unit (PSU) typically struggles to deliver sufficient current during peak component demand, leading to system instability, random reboots, or crashes under load, such as during intense gaming sessions. It would not generally cause an immediate power-on and then shutdown, as the initial power draw for the Power-On Self-Test (POST) is relatively low compared to full system operation.
- ✓
A motherboard standoff is shorting the board to the case
Why this is correct
An improperly placed or missing motherboard standoff can create an unintended electrical connection between the motherboard's traces and the metal computer case, resulting in a direct short circuit. Modern power supply units (PSUs) incorporate robust overcurrent protection mechanisms that detect such shorts. Upon sensing this fault, the PSU will immediately trigger a protective shutdown to prevent damage to the motherboard and other sensitive components, manifesting as a brief power-on followed by an instant cut-off.
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The CPU fan is not connected
Why it's wrong here
If the CPU fan is not connected, the system's BIOS typically detects the missing fan signal during the Power-On Self-Test (POST) and may issue a warning or halt the boot process. While some systems might proceed to boot, the CPU would quickly overheat without active cooling, triggering the processor's thermal throttling mechanisms and eventually a thermal shutdown. This process usually takes several seconds or minutes, not an immediate power-on and shutdown.
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The power supply's voltage selector is set to 230V instead of 115V
Why it's wrong here
Setting a power supply unit's (PSU) voltage selector to 230V when operating in a 115V region means the PSU expects a higher input voltage than it receives. In this scenario, the PSU's internal circuitry, specifically the rectifier and transformer, will not receive sufficient voltage to properly initiate the AC-DC conversion process. This typically results in the PSU failing to power on at all, or a complete and immediate failure, rather than a brief power-on before shutting down.
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