How to Test a Used Phone Screen Before Buying

A great secondhand deal can hide an expensive screen problem. A replacement display is often one of the most expensive repairs on a phone, and a bad panel is the one fault you cannot negotiate away after the fact. Test before you pay.

Set up first

• Meet somewhere with even indoor lighting, not bright sun. Sunlight hides almost everything on a phone screen.
• Ask the seller to turn auto-brightness off and brightness to maximum, and to disable night mode, blue light filters, and any color-tone setting.
• Clean the glass. Fingerprints look like every fault on this list.
• Take five minutes. A seller who won't give you five minutes with the screen is telling you something.

Bring up test patterns

Open this site in the phone's browser and work through the six checks below, each one full-screen. Say up front that you'd like a few minutes with the screen — it is much easier than asking for the phone back later.

1. Dead/stuck pixels

Dead Pixel Test — step through solid colors and scan for wrong-colored dots. Phone pixels are tiny, so look closely. Hold the phone about 20 cm from your eyes and sweep across the screen in strips rather than staring at the centre.

A dot that stays black on every color is dead. One locked on red, green, or blue is stuck and may still be fixable. One that glows white on black is a hot pixel. Dead vs Stuck vs Hot Pixels has the full distinction. On an OLED phone, be aware that dead pixels are rare compared with burn-in — if you find one, it's usually a sign the panel has been replaced or damaged.

2. OLED burn-in

Most phones are OLED. Display a White Screen and a 50% gray (Brightness Uniformity Test) and look for faint ghosts of status bars, navigation buttons, or keyboards.

Grey is the more revealing of the two — burn-in shows up as a slightly darker or pinkish band rather than a hard outline, and pure white can wash it out. Check these places specifically:

• The status bar across the top, including the clock and battery icon.
• The navigation bar or gesture pill at the bottom.
• A rectangular block where a keyboard sits.
• The area around a notch or camera cutout.

Burn-in never improves, and no app fixes it. Grade how bad it is against how much you're saving — a faint status bar on a heavily discounted phone may be fine; a visible keyboard outline is a panel at the end of its life. OLED Burn-In: Causes, Prevention, and How to Check covers what accelerates it, and the Burn-in Test has patterns designed to expose it.

3. Tint and uniformity

A White Screen should be evenly white — watch for pink/green patches or a yellow half (a sign of past damage or aftermarket panels).

Also tilt the phone slowly while a white screen is up. Every OLED shifts slightly blue or green off-axis; that's normal. What isn't normal is a patch that stays discolored at every angle, or a distinct boundary line where one region is warmer than the next. Why Is Part of My Screen Discolored or Tinted? walks through the causes.

Then check a mid-grey for blotchiness — uneven, cloudy patches often mean pressure damage or a panel that has taken a knock.

4. Touch dead zones

In a notes app or drawing app, drag a finger across every part of the screen in one stroke. Any gaps mean a dead touch zone. Draw a tight zigzag so the line covers the full surface, then repeat right along the edges — edge dead zones are the most common and the easiest to miss.

Test multi-touch too: hold one finger still and drag a second. Erratic jumping means a digitizer fault. Try typing a full sentence on the keyboard; a key that needs a second press is a touch problem, not a software one.

5. Cracks and pressure spots

On a Black Screen, look for bright spots or spreading blotches that hint at internal damage even if the glass looks intact.

Black is also the best background for spotting hairline cracks in the glass and any light leaking around the edges. Run a fingernail lightly across the surface — a crack you can feel but barely see will spread. Look for a faint spider-web pattern radiating from one corner: that's an impact the seller may not have mentioned.

6. Flicker

Many OLED phones dim by rapidly switching the panel on and off, which some people perceive as eye strain or headaches at low brightness. Turn the brightness right down and wave your hand in front of the screen — visible stroboscopic banding across your fingers means aggressive flicker. It's not a defect, but it is worth knowing before you buy. What Is PWM Flicker and How Do You Test for It? explains what to look for.

Bonus

Check True Tone/auto-brightness behave, and that the panel is genuine (aftermarket panels often show worse color and touch issues). On iPhones running iOS 15.2 or later, Settings → General → About lists parts and service history, and a replaced display is flagged there on iPhone 12 and newer models (iPhone 11 and earlier show battery history only). On Android, a suspiciously deep discount plus a slightly-off color balance and a rubbery-feeling touch response usually means a third-party panel.

If more than one of these checks fails, walk away — a phone with a good screen is worth paying more for than one with a good battery, because the battery is the cheap part to replace.