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220-1102 Practice Question: A technician is replacing a power supply in a…
A technician is replacing a power supply in a desktop computer. After unplugging the unit, what additional step should be taken to ensure personal safety before touching internal components?
⚠ Common exam trap
CompTIA often tests the distinction between ESD protection (anti-static wrist strap) and electrical safety (discharging capacitors), causing candidates to mistakenly choose the wrist strap as the primary safety step after unplugging.
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
✓
Press and hold the power button for 10 seconds.
After unplugging the power supply, pressing and holding the power button for 10 seconds discharges residual electrical charge stored in the system's capacitors (especially in the power supply and motherboard). This step, often called a 'parasitic drain,' ensures that no stored voltage remains that could cause an electric shock or damage components when touched. It is a standard safety practice before working inside a desktop computer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Wear an anti-static wrist strap.
Why it's wrong here
Wearing an anti-static wrist strap is a crucial safety measure designed to protect sensitive electronic components from electrostatic discharge (ESD) by equalizing the electrical potential between the technician and the computer chassis. However, this device does not provide any protection against the high-voltage electrical charge that can remain stored within a power supply's capacitors, even after the unit has been unplugged. Therefore, while good for component safety, it does not mitigate the risk of electrical shock to the technician from a charged power supply.
- ✓
Press and hold the power button for 10 seconds.
Why this is correct
Pressing and holding the power button for approximately 10 seconds is the correct and safest procedure to discharge residual electrical energy stored within the power supply's capacitors. Even after a computer is unplugged from its AC power source, these capacitors can retain a significant and dangerous voltage for an extended period. This action provides a discharge path through the system's internal circuitry, allowing the stored energy to dissipate safely, thereby eliminating the risk of electrical shock when handling the power supply.
- ✗
Remove the CMOS battery.
Why it's wrong here
Removing the CMOS (Complementary Metal-Oxide-Semiconductor) battery serves the specific purpose of powering the motherboard's real-time clock (RTC) and non-volatile BIOS memory, preserving system settings like date, time, and boot order when the main power is off. While removing it will reset these BIOS configurations, it has no electrical connection or influence over the high-voltage capacitors within the main power supply unit. Consequently, this action does not contribute to discharging any residual power stored in the PSU and offers no safety benefit regarding electrical shock.
- ✗
Unplug all peripheral cables.
Why it's wrong here
Unplugging all peripheral cables, such as USB devices, monitors, and network connections, is a recommended general practice to prevent accidental damage or interference during hardware maintenance and to ensure the system is fully isolated. However, these external connections are entirely separate from the internal power supply unit's primary function and its ability to store residual electrical charge. Disconnecting peripherals does not create a discharge path for the high-voltage capacitors within the power supply itself, which remain a potential hazard even after all external cables are removed.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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