How to Test a Used Monitor Before Buying
Monitors are one of the best second-hand buys in tech — and one of the easiest to get wrong, because the faults that matter most are invisible on a normal desktop. Bring a laptop and your own cables, ask to dim the room, and work through this in about ten minutes before you pay.
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Check for dead and stuck pixels
Fill the screen with red, green, blue, white and black in turn. A dead pixel stays black on every colour; a stuck pixel stays one colour throughout. Both vanish against a normal desktop, so this is the check sellers most often miss honestly.
Open the dead pixel test → -
Look for backlight bleed and IPS glow
Display solid black in a dark room. Bright patches along the edges are backlight bleed; a corner haze that shifts as you move your head is IPS glow, which is normal. Heavy bleed is permanent and worth a discount — the classic mistake is judging this in a bright room, where it is invisible.
Use the black screen → -
Check an OLED panel for burn-in
If the monitor is OLED, this is the single biggest risk to its value. Use flat mid grey in a dim room and look for a faint taskbar strip along the bottom or a HUD outline in the centre. Ask what the monitor was used for — one game or one dashboard for years is far riskier than mixed use.
Open the burn-in test → -
Verify the refresh rate really matches the listing
A model line often spans 60Hz, 144Hz and 165Hz versions that look identical from the outside. Measure the actual rate rather than trusting the badge, and remember it needs enabling in display settings first — a 60Hz reading is usually a setting or a cable, not a lie.
Open the refresh rate check → -
Test colour and gradients
Check for banding in gradients, colour casts and tint differences between the left and right halves. An ageing backlight often yellows unevenly, which is very hard to unsee once you have paid for it.
Open the screen test → -
Check brightness uniformity
On a full white screen, look for darker patches or dimmer corners. Some falloff is normal on large panels; obvious blotches point to a failing backlight and a monitor near the end of its life.
Open the brightness test → -
Test every input port
Plug into each port in turn — DisplayPort, every HDMI, and USB-C if fitted. A dead port is a common fault and easy to hide by only demonstrating the one that works. If the monitor has a built-in USB hub, test that too.
Inspected on the monitor itself — no tool needed.
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Work through the on-screen menu
Press the physical buttons or joystick and open every OSD section. Confirm the controls respond and that features the listing mentions — HDR modes, overdrive, picture-by-picture — are actually present. Worn buttons and a dying joystick are common on heavily used monitors.
Inspected on the monitor itself — no tool needed.
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Inspect the stand, mount and coating
Check the stand holds its height and tilt without sagging, and that the VESA holes are undamaged if you plan to arm-mount it. Look across the panel at an angle for scratches and for patchy or cloudy areas where the matte coating has been rubbed off by aggressive cleaning — that damage is permanent.
Inspected on the monitor itself — no tool needed.
Red flags — negotiate hard or walk away
- Dead or stuck pixels the seller did not disclose. These cannot be repaired.
- Heavy backlight bleed visible on a black screen in a dark room.
- Any visible burn-in on an OLED panel — it will only get worse.
- A measured refresh rate well below the advertised figure that a DisplayPort cable and a settings change do not fix.
- Obvious colour tint differences between one side of the panel and the other.
- A dead input port, or an OSD joystick that no longer responds.
- Patchy, cloudy areas where the matte coating has been rubbed away.
- A seller who will not let you connect your own laptop or dim the room.
Frequently Asked Questions
How many dead pixels are acceptable on a used monitor?
Manufacturers typically only accept a warranty return at three to five, and many exclude single stuck pixels. On a private sale it is your call — but the fault is unrepairable, and one near the centre is far more distracting than one at the edge, so treat any as grounds to negotiate.
What is the difference between backlight bleed and IPS glow?
Bleed is light escaping around the panel edges — bright patches on a black screen, visible from any angle, and a manufacturing flaw. IPS glow is a corner haze that shifts as you move your head and is normal for IPS panels. Bleed stays put; glow moves.
Should I avoid buying a used OLED monitor?
Not automatically, but inspect it harder and expect a bigger discount. Burn-in is permanent and invisible on ordinary content, and risk depends entirely on how the screen was used — so test with flat grey in a dim room and ask what it displayed most.
How do I check the refresh rate of a monitor I am buying?
Connect a laptop and run a browser refresh rate test. Set the rate in display settings first — Windows and macOS default to 60Hz. If the high rate is not offered, try DisplayPort; HDMI 1.4 cannot carry 1080p or 1440p at 144Hz.
What should I bring when viewing a used monitor?
A laptop and your own DisplayPort and HDMI cables, so a faulty cable cannot be blamed for a faulty port and you can verify the full refresh rate. A room you can darken matters too — bleed and burn-in are invisible in bright light.