How to check the screen of a used phone or laptop

Updated September 26, 2026

The screen is the most expensive part of a phone or laptop: a genuine screen replacement on a recent iPhone can cost a large share of what you paid for the phone. That makes a careful screen check the single most worthwhile thing to do when buying used. This guide explains each kind of defect, how to spot it and how serious it is.

Get ready

Turn brightness all the way up, and turn off dark mode and Night Shift or any blue-light filter.
Wipe the screen clean: dust and fingerprints are easily mistaken for dead pixels.
If you can, check in a slightly dark room so backlight bleed is easier to see.

Then use Soi Máy's full-screen colour test:

Dead pixel, backlight bleed and burn-in testFind dead or stuck pixels, backlight bleed, burn-in and lines on a phone or laptop screen. Eight full-screen colours, free, no app to install.

Dead, hot and stuck pixels

Dead pixel: a dot that is always black, easiest to see on white or bright colours.
Hot pixel: a dot that is always white or bright, easiest to see on black.
Stuck pixel: a dot stuck on one colour (red, green or blue), visible when other colours are shown.

Look at every colour carefully, including all four corners and along the edges. A dead pixel in the middle of the screen is irritating in daily use; one in a corner matters less but is still a reason to negotiate.

Burn-in on OLED screens

OLED/AMOLED screens (iPhone X and later except the XR, 11 and SE, and most mid-range and flagship Android phones) can suffer burn-in: things shown for a long time, such as the status bar, keyboard or navigation bar, leave a permanent ghost image.

To check: fill the screen with neutral grey and look closely while tilting the phone. A faint keyboard or top bar means burn-in. Light burn-in visible only on grey is livable, but the phone should be cheaper.

Backlight bleed on LCD screens

LCD screens (most laptops, iPhone 11, XR and SE, many budget Android phones) use a backlight and can show backlight bleed: bright patches at the edges or corners on a black screen. Check with black in a dark room. Slight glow in the corners is normal for LCDs; bright patches spreading into the middle are a defect.

Yellow stains, blotches, lines

On white, look for yellowish or uneven patches: usually from pressure damage, water or failing adhesive.
On the gradient, colours should blend smoothly from black to white. Bands or broken steps point to a problem with the panel or its cable.
Fixed vertical lines in green, pink or white are a hardware fault that won't go away.

Replacement screens

Non-genuine screens often show:

Washed-out colours, lower peak brightness, narrow viewing angles.
On iPhone: "Unknown Part" in Settings › General › About, and usually no True Tone.
On Android: an in-display fingerprint sensor that works poorly or not at all.
Glue showing around the edge, or glass that sits proud of the frame.

Dead zones and ghost touches

A screen that looks perfect can still have a faulty touch layer. With one finger, swipe to fill the grid: an area that never fills is a dead zone, cells that fill without a touch are ghost touches.

Touch screen test: dead zones and ghost touchesSwipe to fill a grid of cells and spot dead touch zones or ghost touches on a phone or tablet. Runs full screen, free.

Also check multi-touch: a phone should register at least 5 fingers at once, which matters for games.

90/120 Hz refresh rate

If the device is sold with a 90 Hz or 120 Hz screen, measure it. Turn off battery saver first, since it usually locks the screen to 60 Hz. On iPhone, browsers are limited to 60 Hz, so the test explains a separate way to check.

Screen refresh rate test (Hz)Measure the real refresh rate of a phone or laptop screen (60, 90, 120, 144 Hz) and check that motion is smooth. Includes iPhone ProMotion instructions.

In short: which defects matter?

Don't buy (unless it is very cheap and you plan to replace the screen): fixed lines, dead zones or ghost touches, large stains, burn-in visible in normal use.
Negotiate: a few dead pixels in a corner, light burn-in visible only on grey, a good-quality replacement screen.
Acceptable: slight corner glow on an LCD.

See also the guides to buying a used iPhone, Android phone and laptop.