Lines appearing on your computer monitor or laptop screen are among the most common display problems users encounter. Whether you are seeing vertical lines on monitor, horizontal lines on monitor, or unusual coloured lines on screen, understanding the cause is the first step toward finding a solution.

Monitor Lines Problem: Diagnose and Fix Lines on Your Screen

Why Your Monitor Has Lines (and What Type You Have)

A monitor lines problem refers to any situation where straight lines — vertical, horizontal, coloured, or static — appear on your screen and do not go away. These lines persist across all applications, desktops, and boot screens, which distinguishes them from software glitches that come and go.

The lines can be:

• Black or dark: Usually indicate a dead row or column of pixels caused by panel damage or ribbon cable failure
• Coloured: Green, red, purple, or pink lines typically point to signal transmission or sub-pixel circuit failures
• White or faint: Often linked to LCD panel ageing, static discharge, or T-Con board issues
• Single or multiple: A single thin line may indicate a specific transistor failure; multiple lines may suggest broader cable or panel damage

The first question to answer is: what type of line do you have? The direction and colour of the line tells you a great deal about the cause and the fix.

Horizontal vs Vertical vs Coloured — What the Direction Tells You

The direction of a line is the most important diagnostic clue. It tells you exactly which part of the display circuitry has failed.

Vertical lines (top to bottom):

• Point to column electrode failures — the vertical signal pathways that carry data to each pixel column
• Common causes: ribbon cable damage, T-Con board column output failure, aging panel column circuits
• See the vertical LCD lines guide for detailed repair steps

Horizontal lines (left to right):

• Point to row electrode failures — the horizontal signal pathways that select which pixel row to update
• Common causes: gate driver circuit issues, ribbon cable damage, panel row circuit degradation
• See the horizontal LCD lines guide for detailed repair steps

Coloured lines (green, red, purple, pink):

• Point to sub-pixel channel failures — a specific colour channel is broken, while others work
• Green line: red and blue sub-pixels failing; Red line: green and blue failing
• Purple/pink line: red sub-pixels failing (blue dominant)
• See the coloured lines guide for detailed repair steps

White or static lines:

• Point to panel-level circuit issues — entire rows of sub-pixels stuck in the "on" position
• Often accompany aging monitors or T-Con board timing failures

The colour table for sub-pixel failures:

LVDS/eDP Cable: The #1 Culprit for Monitor Line Problems

The display cable — whether LVDS (older monitors), eDP (modern monitors and laptops), HDMI, DisplayPort, or USB-C — is the single most common cause of lines on a monitor or laptop screen.

Why cables cause lines:

Each display cable carries signals for hundreds or thousands of pixel columns and rows simultaneously. These signals travel as discrete electrical pulses through individual conductors inside the cable. When one of these conductors cracks, bends, or partially disconnects, the signal for specific pixel columns or rows becomes corrupted.

The result is a vertical line (if a column conductor fails) or horizontal line (if a row conductor fails), depending on which signal pathway is affected.

Cable types and their vulnerabilities:

• eDP (embedded DisplayPort): Used in modern laptops and monitors. Carries all display signals on a single thin ribbon cable. Vulnerable to flex damage at hinges (laptops) or bending stress (monitors).
• LVDS: Used in older monitors. Uses multiple conductors in a ribbon cable. Individual conductors can crack over time.
• HDMI/DisplayPort: External cables. Vulnerable to connector wear, cable bending, and electromagnetic interference. Less likely to cause persistent lines than internal cables.
• USB-C/Thunderbolt: Carries display signals alongside data and power. Less common cause of line issues but can fail at the connector.

Signs your cable is the culprit:

• Lines appeared after moving the monitor or laptop
• Lines flicker or change when you move or bend the cable
• The line is thin and perfectly straight
• A different cable produces the same line (confirms the monitor's internal cable, not the external cable)

Fix: Reseat or replace the internal display cable. On laptops, the flex cable replacement typically costs $10–$30. On monitors, internal ribbon cable replacement typically costs $15–$40.

T-Con Board Failure — The Most Common Aging Monitor Issue

The T-Con board (timing controller) is the most likely culprit when a monitor that is more than two years old develops lines. It is also the most commonly misdiagnosed component — users often assume they need a new panel when only the T-Con board needs replacing.

What the T-Con board does:

The T-Con board receives the video signal from your computer and translates it into the precise voltage signals needed for each sub-pixel on the LCD panel. It contains:

• Row driver outputs (for horizontal lines)
• Column driver outputs (for vertical lines)
• Timing circuits that synchronise the display refresh

How T-Con failure produces lines:

When one of the column driver outputs fails, an entire column of pixels stops receiving the correct data signal. The column either goes dark (black line) or gets stuck displaying a single colour (coloured line).

When one of the row driver outputs fails, an entire row of pixels does the same — producing a horizontal line.

Signs of T-Con failure:

• The line is perfectly straight and runs the full width (vertical) or height (horizontal) of the screen
• The line stays in exactly the same position on all inputs
• The line does not flicker when you move the monitor
• A different computer produces the same line
• The monitor is more than two years old

T-Con replacement cost guide:

Before ordering: Open the monitor and photograph the existing T-Con board. The part number is printed on the label — search for it on eBay or Amazon for an exact match. T-Con boards are model-specific; generic replacements may not work correctly.

Panel Circuit Damage — When the Screen Itself Is Failing

Some lines cannot be fixed by replacing cables or the T-Con board because the panel itself is failing. This is the most serious type of monitor line problem.

How panel circuit damage works:

Inside every LCD panel are microscopic conductive traces — called column electrodes and row electrodes — that run through the glass. These traces carry electrical signals from the panel's edge connectors to each pixel. When one of these traces degrades or breaks, the pixels in that column or row stop receiving signals, producing a persistent line.

Why panel damage is different from cable or T-Con damage:

• Cable damage: the signal is not reaching the panel correctly
• T-Con damage: the signal is being generated incorrectly
• Panel damage: the signal reaches the panel but the panel cannot process it

Panel circuit traces are embedded in the glass and cannot be repaired. The only fix is panel replacement.

Signs that the panel itself has failed:

• Lines appeared suddenly with no trigger (no movement, bump, or driver change)
• Lines are perfectly stable — they never flicker or change
• New lines are appearing adjacent to existing ones
• The monitor is more than five years old
• Replacing the T-Con board and cables did not resolve the issue
• Multiple lines are spreading across the screen

Panel replacement cost guide:

The 50% rule: If the repair cost exceeds 50% of the device's current replacement value, it is usually better to replace the monitor entirely.

Monitor Repair vs Replacement — The $50 Decision Framework

When lines appear on a monitor, the key question is: repair or replace?

Here is a practical decision framework:

Repair the monitor if:

• The monitor is less than three years old
• The repair cost is less than 50% of the monitor's current value
• The monitor has special characteristics that are hard to replace (high refresh rate, colour accuracy, specific panel type)
• You have a warranty that covers the repair
• The line appeared suddenly after a specific event (moving, bumping) that points to a loose cable

Replace the monitor if:

• The monitor is more than five years old
• The repair cost exceeds 50% of the current replacement value
• Panel replacement is required (most expensive fix)
• Multiple problems exist (lines, dead zones, backlight issues)
• You have been planning to upgrade anyway

Repair cost reference:

Real Case: A BenQ PD3220U User's $35 T-Con Board Fix

A BenQ PD3220U (4K USB-C monitor) owner reported two thin vertical lines appearing near the centre of the screen. The lines had appeared gradually over several weeks and were visible on all inputs.

Initial assumption: The panel was failing and the monitor needed replacement ($400–$600).

Diagnosis steps:

1. Connected the monitor to a different laptop with a different cable — same lines appeared. Confirmed the issue was in the monitor, not the source.
2. Searched for the BenQ PD3220U service manual online — found disassembly instructions on iFixit.
3. Opened the monitor back panel (12 screws around the perimeter).
4. Located the T-Con board near the bottom edge — photographed the label showing the part number.
5. Searched eBay for "BenQ PD3220U T-Con board" — found an exact replacement for $35.
6. Replaced the board, reassembled the monitor.
7. Both vertical lines disappeared completely.

Total cost: $35 for the replacement board.

Key takeaway: Before replacing a monitor that is showing lines, identify the component that is actually failing. A $35 T-Con board replacement saved a $500 monitor from being replaced.

How to Test for Monitor Lines (Step-by-Step)

Follow this testing sequence to diagnose the cause of your monitor lines:

Step 1: Use the screen test tool

Open our free screen test tool and run through the following colour tests:

1. Pure black background — dark lines (black, coloured) will be immediately visible against the dark background
2. Pure white background — bright lines (white, coloured) will stand out
3. Pure red background — a line visible here but not on other colours indicates a specific sub-pixel channel failure
4. Pure green background — same principle
5. Pure blue background — same principle

Step 2: Note the line characteristics

• Position: Is it vertical or horizontal? Where on the screen (top, bottom, centre, left, right)?
• Colour: Is it black, white, green, red, purple, or another colour?
• Width: Is it one pixel wide, several pixels wide, or many millimetres wide?
• Count: Is it a single line or multiple lines?
• Behaviour: Does it flicker? Does it change with cable movement?

Step 3: Test on a different device

• Connect the monitor to a different computer using the same cable
• If lines persist: the issue is in the monitor (hardware)
• If lines disappear: the issue is in the source computer (GPU, drivers, or port)

Step 4: Test with a different cable

• Replace the HDMI, DisplayPort, or USB-C cable
• If lines persist: the monitor's internal hardware is the issue
• If lines disappear: the external cable was the cause

Related Monitor Line Problems

Our guides cover every specific type of monitor line:

• Vertical and Black Lines on Monitor: Covers vertical lines, black vertical lines, and small black lines
• Coloured Lines on Monitor: Covers green lines, red lines, purple lines, and pink lines
• Horizontal Lines on Monitor: Covers all horizontal line types
• White and Static Lines on Monitor: Covers white lines and static-like interference

Related Display Issues

Monitor lines can be confused with other display problems. Explore these related guides:

• Black Line on Screen: Thin black lines across your screen — distinct from vertical lines, though causes often overlap
• Green Line on Screen: Persistent green lines — related to coloured line issues
• White Line on Screen: Bright white lines — shares causes with static and white line problems
• Dead Pixel: Individual stuck or dead pixels that may appear as tiny lines
• Dead Line of Pixels: A line of dead pixels that looks similar to hardware lines
• Screen Flickering: Flickering sometimes accompanies line problems — both stem from cable or panel issues

Conclusion

Monitor lines — whether vertical, horizontal, coloured, or static — share common underlying causes related to panel circuitry, ribbon cables, and signal transmission. Start by using our screen test tool to identify the exact type of line. Work through the diagnosis: test on a different device, try a different cable, then open the monitor to check internal cables and the T-Con board. Most monitor line problems cost $15–$50 to fix with a T-Con board replacement. Only replace the panel if the repair cost exceeds 50% of the monitor's current value.