220-1101 Question 452
Single answerExternal interferenceA technician is troubleshooting an office user's wireless keyboard and mouse that both connect through a single 2.4 GHz USB receiver. The devices work normally early in the morning, but around lunchtime the pointer becomes erratic and keystrokes are delayed or missed. The batteries are new, the devices are within 3 feet of the computer, and reinstalling the drivers did not help. The technician notices a recently installed break-room microwave on the other side of the cubicle wall. Which of the following is the MOST likely cause of the problem?
- A
Radio frequency interference from the microwave affecting the 2.4 GHz wireless receiver
- B
A corrupted HID driver causing intermittent failure only during high CPU usage periods
- C
An IP address conflict between the keyboard receiver and another wireless device on the network
- D
Insufficient power from the USB port because the keyboard and mouse are using a shared receiver
Show answer and explanation
Correct answer: A
Explanation
The best answer is radio frequency interference from the microwave. In A+ Core 1 troubleshooting, external interference is a common cause of intermittent problems with wireless peripherals, especially devices operating in the 2.4 GHz range. A key troubleshooting principle is to correlate symptoms with environmental changes or timing patterns. Here, the issue appears around lunchtime and a new microwave was installed nearby, making EMI/RFI the most likely cause. Practical remediation would include moving the receiver to a front USB port or extension cable, increasing distance from the interference source, or switching to a different wireless technology or frequency if available. This aligns with standard vendor guidance for wireless peripherals and general best practices for mitigating electromagnetic and radio frequency interference.
- A. Correct.
Correct. Many wireless keyboards and mice use the 2.4 GHz band, which can be affected by external sources of radio frequency interference. Microwave ovens commonly emit interference in or near the 2.4 GHz range, and symptoms such as intermittent lag, missed keystrokes, and erratic pointer movement that occur when the microwave is in use strongly indicate external interference rather than a device failure.
- B. Incorrect.
Incorrect. A corrupted HID driver would typically cause persistent or repeatable input issues regardless of time of day, not a pattern tied to lunchtime. The scenario also states that reinstalling drivers did not help, which further reduces the likelihood of a driver-related issue.
- C. Incorrect.
Incorrect. Standard wireless keyboard and mouse receivers do not obtain IP addresses and do not participate on the network like Wi-Fi clients. This distractor targets a common misconception that all wireless devices use TCP/IP networking.
- D. Incorrect.
Incorrect. A shared USB receiver is normal for many keyboard and mouse combos and does not by itself indicate a power problem. USB power issues would be more likely to produce constant disconnects or complete device failure rather than time-specific interference that matches microwave usage.