How to Check a Used Monitor Before You Buy

Bring the right setup

If possible, bring a laptop with the correct HDMI or DisplayPort cable and open ScreenVitals before the meeting. Confirm that your device can drive the monitor’s native resolution and advertised refresh rate. A phone browser is useful for TVs and smart displays, but it cannot verify every input or computer-specific feature.

• A known-good video cable and power cable
• A laptop with the required output or adapter
• A clean microfiber cloth
• Your phone camera for documentation
• The listing, receipt, model number, and claimed warranty details

1. Inspect the hardware before powering on

Check the panel surface from several angles under normal light. Look for scratches, pressure marks, coating damage, cracks, gaps in the bezel, loose ports, missing screws, or signs that the enclosure has been opened. Smell near the vents for overheating or smoke damage, but do not open the device.

Confirm that the stand adjusts correctly and stays stable. For VESA-mounted displays, inspect the mounting threads. A perfect panel is not useful if the stand, controls, or ports are damaged.

2. Confirm identity, resolution, and refresh rate

Compare the model label with the seller’s listing. In the operating-system display settings, choose the native resolution and check the available refresh rates. Run the refresh rate test with the browser fully on that display. A browser result close to the selected setting is a useful check, though it is not certified hardware measurement.

3. Check dead and stuck pixels

Run red, green, blue, white, and black full-screen patterns. Scan slowly rather than staring at one point. Clean suspected marks and compare them across colors. A black point on every bright color may be dead; a point that stays bright or colored may be stuck.

Count and photograph suspected defects. Warranty policies can treat bright, dark, clustered, and central defects differently, so avoid assuming one universal threshold.

4. Check black level and edge lighting

In a dim room, use the black pattern at normal brightness. On LCD displays, compare fixed edge patches with glow that changes when you move. On OLED, black should be very dark, but raised blacks may come from settings, ambient light, or browser/HDR behavior.

5. Check gray uniformity and OLED wear

Inspect 5%, 10%, 20%, and 50% gray. Pan a uniform field and look for stationary streaks, cloudy patches, tint, or a faint taskbar, logo, or game HUD. Some variation is visible on many panels under stress patterns; decide whether it is visible during normal content at your viewing distance.

6. Test ports, controls, audio, and sleep

Test every port you intend to use, not just the seller’s connected input. Open the on-screen menu and check buttons or joystick controls. Verify speakers, USB hubs, KVM functions, brightness control, standby, wake behavior, and power delivery where applicable. Leave the display running long enough to reveal intermittent flicker or heat-related shutdown.

7. Save evidence before paying

Photograph the model and serial label, any visible defect, the powered-on screen, and the included accessories. Keep the original listing and conversation. If the seller claims transferable warranty coverage, verify what documentation and ownership conditions the manufacturer requires.