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220-1201 Practice Question: That their desktop computer's display is very…
A user reports that their desktop computer's display is very dim, even at maximum brightness settings. The monitor is an older LCD model with a CCFL backlight. What component is most likely failing?
⚠ Common exam trap
CompTIA A+ often tests the misconception that a dim display is always caused by a failing LCD panel or a bad video cable, when in fact the backlight subsystem (inverter or CCFL) is the most likely culprit in older monitors with CCFL technology.
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
✓
The inverter board
The inverter board is responsible for converting DC power from the power supply into the high-voltage AC required to drive the CCFL (cold cathode fluorescent lamp) backlight in older LCD monitors. When the inverter fails, the backlight either dims significantly or fails entirely, even though the LCD panel itself may still be receiving a valid video signal and the brightness controls appear to function. This matches the symptom of a very dim display at maximum brightness settings.
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 LCD panel itself
Why it's wrong here
A failing LCD panel, which comprises the liquid crystal matrix and color filters, primarily manifests issues related to image integrity. This includes symptoms like distorted images, persistent lines (horizontal or vertical), stuck pixels, or completely dead pixels (black spots). Uniform dimness across the entire display indicates a problem with the backlight illumination system, not the image-forming capabilities of the panel itself.
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The inverter board
Why this is correct
The inverter board is a critical component in older LCD monitors, responsible for converting the low-voltage DC power from the power supply into the high-voltage AC required to illuminate the Cold Cathode Fluorescent Lamp (CCFL) backlight. If the inverter fails or degrades, it cannot supply sufficient voltage to the CCFL, resulting in a significantly dimmed display or a completely black screen. This uniform dimness is a hallmark symptom of an inverter malfunction.
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The video cable
Why it's wrong here
The video cable (e.g., VGA, DVI, HDMI, DisplayPort) is responsible for transmitting the digital or analog video signal from the computer's graphics card to the monitor. A faulty or loose video cable typically results in signal integrity issues, manifesting as flickering, color distortion, horizontal or vertical lines, "no signal" messages, or a completely blank screen. It does not control the backlight intensity, so it would not cause a uniformly dimmed display.
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The power supply unit
Why it's wrong here
The power supply unit (PSU) in a desktop computer delivers electrical power to all internal components, including the motherboard, CPU, storage drives, and graphics card. A failing PSU typically results in system-wide power instability, leading to spontaneous shutdowns, reboots, failure to power on, or intermittent component operation. While the monitor has its own power supply, a computer's PSU failure would not selectively cause only the display to be uniformly dim while the rest of the system operates normally.
Go deeper
Related to this question
Learn chapter
Power Supply Units and Connectors
Key term
Inverter
An inverter is a circuit in a mobile device's display assembly that converts DC power into AC power to light the backlight, typically in older LCD screens.
Key term
Backlight
A backlight is a light source behind a liquid crystal display (LCD) that illuminates the screen so you can see the images and text.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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