Check a screen before you buy, sell or worry

Look across the whole screen on each colour from about 50 cm, then closer along the edges and corners.

Look across the whole screen on each colour at reading distance, then closely along the edges, the corners and around the camera hole.

• Dead pixel: a dot that stays dark on the white screen.
• Stuck pixel: a dot that stays red, green or blue. It stands out on black and on the colours it does not belong to.
• Line: a thin line across the whole screen points to a panel or cable fault, which is more serious than one pixel.
• Dust or a pixel? Dust looks soft and moves with your viewing angle; a pixel fault is a sharp square that stays put.

OLED screens, which most phones use, wear where the same image stays for hours. Turn brightness to full for this test and look for faint shapes that should not be there.

• Status and navigation bars: a faint strip or icons along the top or bottom edge, clearest on grey.
• Keyboard and app layouts: the outline of keys or of a much-used app in the lower half.
• Colour shift: on white, worn areas look slightly yellow or pink compared with the rest.
• Retention or burn-in? Retention fades within minutes of showing something else; burn-in stays.

Turn brightness down to about 10% in a dim room. OLED faults that a bright screen hides show up here.

• Graininess: a fine, sandy texture. A little is normal for OLED at very low brightness; blotches you can see at arm's length are not.
• Tint: parts of the dark grey look green or pink, often along one edge.
• Black crush: the darkest grey looks like pure black, or the dark greys jump in steps.

Use the black screen in a dim room at your normal brightness, not at maximum. Look from straight in front, then move your head a little.

• Bleed: bright patches along an edge or in a corner that stay in place when you move your head.
• Glow: a haze that shifts or grows as your viewing angle changes. Some glow is normal for LCD panels, especially IPS; VA panels usually show less.
• Clouding: blotchy lighter areas across the black.

Mid and dark greys reveal differences that white and black hide.

• Uneven brightness: a corner or band that is clearly darker than the centre. A slight fall-off towards the edges is normal.
• Tint patches: areas that look pinkish, yellowish or greenish compared with the rest.
• Pressure marks and smudges: ripples, spots or a dirty-looking patch that is not on the glass.
• Image retention: a faint ghost of a taskbar or window. On LCDs it normally fades within minutes.

Each ramp has all 256 levels from dark to bright. It should look smooth.

• Banding: visible steps or stripes in a ramp.
• Colour cast: the grey ramp turning greenish or pinkish in places.
• Not always the panel: graphics-card colour settings, a non-native mode or a cheap cable adapter can cause banding too. If in doubt, compare with another monitor on the same computer.

These patterns are drawn one panel pixel at a time, whatever the Windows scaling. At the native resolution they look like flat, even grey from a normal distance and a crisp fine grid close up.

• Waves, stripes or blur mean the picture is being scaled: check the resolution above, the browser zoom, or the monitor's sharpness setting.
• Text: the last screen shows text at several sizes. Small text should be readable without colour fringes.
• Pixel density: a 27-inch Full HD screen has about 82 pixels per inch, so text is softer than on a 24-inch Full HD or 27-inch QHD screen. That is normal, not a fault.

The screen turns into a grid. Slide a finger over every cell until all of them are filled; the counter shows how many are left.

• Dead zone: cells that never fill, usually in a strip or a corner. Go over them slowly once more before calling it a fault.
• Edges: run along every edge and corner too; curved edges and replaced screens tend to fail there first.
• To finish: once every cell is filled, tap anywhere, or use the back gesture at any time. The result is written into the note below.

Each finger on the screen draws a circle. Add fingers one at a time; the top of the screen shows how many registered at once.

• Fingers at once: phones and tablets normally track at least five. Fewer, or circles that jump about, point to a touch-panel fault.
• Ghost touch: lift every finger and leave the phone untouched for 30 seconds. No circle should appear and the touch count should not rise.
• To finish: use the phone's back gesture.

Blocks cross the screen at a constant speed on dark, mid and light backgrounds. The measured refresh rate is shown in the corner.

• Ghosting: a long smeared trail behind a block. VA panels often smear more on the dark background; that is typical, but compare it with the other two lanes.
• Overshoot: a bright or dark outline that the block drags behind it, usually from the monitor's highest overdrive setting.
• Judder: jumps instead of smooth movement. Check the refresh rate and close heavy programs.

No test screen for this one: check the device itself.

• Scratches: switch the screen off and look at an angle with a window or lamp reflected in it. Scuffs on the coating show only this way.
• Buttons and menu: every button works, and the monitor's information menu shows the expected resolution and refresh rate.
• Ports: each input gives a picture with your cable.
• Stand and casing: adjustments hold, nothing wobbles or rattles, and there are no cracks.
• Noise: no buzzing or high-pitched whine at your normal brightness.
• Rear label: the model and manufacture date match what you were told.

• Glass: with the screen off, tilt it under a light to find scratches and hairline cracks, especially at the corners.
• Gaps and lifting: the screen should sit flush with the frame. A gap or a bulging screen can mean a swollen battery; stop using the phone.
• Screen protector: bubbles or cracks in a protector are not the screen's. Lift a corner only if the owner agrees.
• Fingerprint sensor: on phones with one under the screen, test it; a cracked or replaced screen often breaks it.
• Buttons and sensors: the volume and side keys work, and the screen turns off when you cover the top during a call (proximity sensor).

Get-CimInstance -Namespace root\wmi -ClassName WmiMonitorID | ForEach-Object {
  [pscustomobject]@{
    Model = -join ($_.UserFriendlyName | Where-Object { $_ } | ForEach-Object { [char]$_ })
    Year  = $_.YearOfManufacture
    Week  = $_.WeekOfManufacture
  }
}