220-1101 Question 303
Single answerInput 110–120 VAC vs. 220–240 VACA technician in the United States is deploying a desktop PC that was shipped from a country using 220–240 VAC mains power. After plugging the system into a standard U.S. wall outlet, the PC does not power on. During inspection, the technician notices the power supply has a manual voltage selector switch set to 230V. What should the technician do FIRST to safely power the system in the new location?
- A
Move the power supply selector to 115V while the system is unplugged, then connect it to the U.S. outlet and test it
- B
Use a passive plug adapter so the 230V setting can remain unchanged on the U.S. outlet
- C
Replace the motherboard because it is incompatible with 110–120 VAC input
- D
Connect the PC to a UPS to automatically convert 110–120 VAC into 230V for the power supply
Show answer and explanation
Correct answer: A
Explanation
This question tests practical troubleshooting of regional AC input voltage differences, a common A+ Core 1 topic. In North America, standard mains voltage is typically 110–120 VAC, while many other countries use 220–240 VAC. On older or manually switchable power supplies, the input selector must match the local supply. If a PSU is set to 230V and connected to a 115V source, the system often will not power on properly. Best practice is to disconnect power before changing the selector. Modern power supplies are often autosensing and support a wide input range such as 100–240 VAC, but when a manual selector is present, the technician must verify and set it correctly. This aligns with standard PC hardware support procedures and manufacturer documentation for legacy ATX power supplies.
- A. Correct.
Correct. In the United States, standard wall power is typically 110–120 VAC. If a power supply has a manual input voltage selector, it must be set to match the local mains voltage before use. The technician should unplug the system first, change the selector to 115V, and then test it. This follows safe handling practices and matches how legacy/manual-switch ATX power supplies are designed to operate.
- B. Incorrect.
Incorrect. A passive plug adapter only changes the plug shape; it does not change the voltage supplied. Leaving the power supply set to 230V and plugging it into a 110–120 VAC outlet may prevent the system from powering on because the PSU is configured for a higher input range than the outlet provides.
- C. Incorrect.
Incorrect. The motherboard does not directly accept wall AC power. The power supply converts AC input to regulated DC rails used by the motherboard and other internal components. The issue in this scenario is the PSU input setting, not motherboard compatibility with AC mains voltage.
- D. Incorrect.
Incorrect. A UPS primarily provides battery backup, surge protection, and in some models voltage regulation, but it does not generally function as a step-up transformer to convert a standard 110–120 VAC wall outlet into 230V output for equipment configured only for 230V input. Assuming a UPS performs this conversion is a common misconception.