How to Check a Used Monitor Before Buying
Ten minutes of checks can save you from buying a screen with dead pixels, a weak backlight or a refresh rate that never works. Here's exactly what to test.
What to Bring
- A laptop with a suitable cable (DisplayPort or HDMI), or ask the seller to have a computer connected.
- A phone with this page open, so you can reach every test quickly.
- A microfibre cloth to wipe dust off the screen before judging pixels.
1. Look for Physical Damage
Before switching on, check the panel at an angle under light:
- Scratches and pressure marks on the screen surface.
- Cracks in the bezel or stand, especially around the mount.
- Bent or loose ports — wiggle the cable gently once connected and watch for flicker.
2. Check for Dead and Stuck Pixels
Open the dead pixel test in full screen and step through each colour. Look slowly across the whole screen, including the corners:
- A black dot on light colours is a dead pixel.
- A bright or coloured dot on black is a stuck pixel.
One stuck pixel near the edge might be acceptable at a big discount; several near the centre usually aren’t.
3. Check the Backlight and Uniformity
Use the black screen in a dim room. Look for:
- Backlight bleed — bright patches leaking in from the edges or corners. Some is normal on IPS panels; large bright blotches aren’t.
- Clouding — uneven patches across the middle.
Then use the grey and white screens to check for darker areas, tinted zones or a yellowed image, which can mean an ageing backlight.
4. Check for Burn-In (OLED and Older Panels)
On the grey screen, look for faint outlines of taskbars, logos or game HUDs. OLED monitors are most at risk; heavy static use can also leave image retention on some LCDs.
5. Confirm the Refresh Rate
If the monitor is sold as 144 Hz, 165 Hz or faster, set that rate in the computer’s display settings, then run the refresh rate test. The measured rate should match the advertised one. If it can’t get past 60 Hz on any port, there may be a hardware or firmware fault.
6. Check Motion Clarity
Run the ghosting test and watch the moving blocks. Try each overdrive setting in the monitor’s menu. A good panel shows a short, faint trail at one of its settings. Long smears on every setting can point to a slow or faulty panel.
7. Test Every Input and Button
- Try each video input you plan to use (DisplayPort, HDMI, USB-C).
- Press every menu button and check the on-screen display responds.
- Check the USB hub and speakers if the monitor has them.
8. Confirm the Model and Resolution
Read the model number on the label at the back and look up its specs. Check the resolution in the computer’s settings matches. The PPI calculator shows how sharp that resolution will look at the screen’s size.
Red Flags: Walk Away
- More than one or two defective pixels near the centre
- Strong backlight bleed or a yellow/dim backlight
- Flicker, lines or image dropouts when the cable moves
- A high-refresh monitor that won’t run above 60 Hz
- Visible burn-in on an OLED
- The seller won’t let you power it on
Price Guide
A used monitor in good condition typically sells for 50–70% of its current new price. Knock more off for cosmetic damage, a missing stand, or minor bleed. Pixel or backlight problems usually mean it’s only worth buying at a steep discount.
Test It Yourself
- Dead Pixel TestFill your screen with solid colours one at a time to spot dead, stuck or hot pixels.
- Monitor Refresh Rate TestFind out how many times per second your screen is really refreshing — and whether your high-refresh monitor is stuck at 60 Hz.
- Monitor Ghosting TestWatch blocks move across three backgrounds and look for trails, blur or bright halos behind them.
- PPI CalculatorEnter a screen's resolution and size to see its pixel density, dot pitch and how close you can sit before pixels become visible.
Key Terms
Published · More in display tests.