Before you buy
Checking a used monitor before you buy
A monitor either works or it does not, which is why people skip checking one. But the faults that matter are all invisible on a desktop wallpaper and all obvious on a flat colour, and they are the difference between a bargain and someone else’s problem.
The run, in order
Confirm the resolution and refresh rate the panel is actually running
Settles the specification in five seconds. A monitor sold as 144 Hz that reports 60 is either being driven by the wrong cable — fixable — or is not the model claimed.
Cycle solid colours across the whole screen
The one fault that cannot be repaired and will never improve. Clean the screen first: dust on black is indistinguishable from a stuck white pixel, and you will find far more dust.
Look at black in the darkest room you can manage
This is where most used monitors lose value, and it is the check nobody does in a bright room. Judge it at the brightness you would actually use, not at maximum.
Look at flat grey while you are still in the dark room
Bleed is looked for on black, this on grey, and it is the half people skip. Vertical banding and blotches are permanent, invisible in a shop and unmissable in any film with a sky in it. Do it now, in the same dark room, while your eyes are still adapted — going back later means adapting again.
Count the near-black and near-white steps you can separate
Catches a panel whose settings have been pushed hard. Most of what it finds is free to fix, so it is worth knowing which you have before you let it change the price.
If both ends looked crushed, check whether it is the panel at all
The negotiation step. A picture with grey blacks or missing shadow detail looks like a tired panel and is very often the graphics card and the screen disagreeing about full and limited range — which costs nothing and takes a minute on your own machine. Worth knowing before you agree a discount for a fault the monitor does not have, and equally before you walk away from a good panel.
Look for tinting and uniformity on solid fields
A cast across the whole screen is a setting. A cast in one region is the panel, cannot be adjusted away, and is a real reason to pay less.
Check the text and the fine colour detail, on your cable
Soft text is almost never the panel, and on a monitor you are about to buy it is worth proving that in thirty seconds. A smeared colour pattern means the link has dropped to reduced colour — the cable, the port, or the monitor identifying itself as a television — and all three are yours to fix afterwards rather than reasons to pay less.
Roll the grey-to-grey transitions, especially the dark ones
The test that matters on a monitor sold for gaming. A panel that trails on the small dark steps is behaving normally for VA and badly for anything sold as fast, and the overdrive setting that fixes it is in the monitor menu. Check it at the seller so you know whether the price matches the panel.
Run the flicker check at the brightness you would actually use
PWM dimming is a property of the panel, cannot be changed, and gives some people headaches within an hour. It is also completely invisible in a five-minute look. If you are sensitive to it, this is the one test on the list that can end a deal for a monitor with nothing else wrong.
Watch a moving pattern at speed
Tells you whether the response actually justifies the refresh rate on the box, which is a different question from ghosting: blur is how long each frame is held and no setting removes it.
Try every input, with your own cable
Not a browser test. Inputs fail individually and a seller who only ever used one port genuinely may not know. Bring the cable you intend to use, because a monitor that works over HDMI and not DisplayPort is worth less to you specifically.
Look for the usage hours in the monitor menu
Many monitors keep a running total, usually under an information or service page in the on-screen menu, and it is the only honest figure about age available at the door. A panel with thirty thousand hours has been on for three and a half years continuously and its backlight has dimmed measurably, whatever the cosmetic condition suggests. Not every model reports it; when it does, it is worth more than the seller's account.
Press gently on the bezel corners and watch for changes
A picture that flickers or shifts under light pressure means a loose internal connection, which is a repair rather than a discount.
Bring these three things
A laptop, the cable you intend to use, and a microfibre cloth. The cloth is not a joke: most reported dead pixels on a used monitor are dust, and finding that out after you have paid is worse than finding it out before.
The order, and why
Resolution first, because it settles what the monitor is before you spend time on how good it is. Then the panel faults that cannot be repaired — pixels, bleed, uniformity — while the room is dark and your eyes are adapted, because going back for them later means adapting again. Then the things that look like panel faults and are usually settings, which is where the range test earns its place. Then motion, then the physical checks. If something in the first three steps ends the deal, you have spent two minutes.
The split that matters is not good against bad. It is permanent against fixable, because only the first kind should change the price.
What each finding is worth
| What you find | What it means for the price |
|---|---|
| Dead pixel, centre of screen | Walk away |
| Dead pixel, far corner | Significant discount if you can live with it |
| Picture changes when you press the frame | Walk away |
| Heavy backlight bleed | Substantial discount |
| Regional colour cast | Substantial discount, cannot be fixed |
| Crushed blacks or clipped whites | Check the range test first — often free to fix and not the panel |
| Banding or blotches on grey | Permanent, and visible in every film with a sky |
| PWM flicker at usable brightness | Walk away if you are sensitive; irrelevant if you are not |
| Trailing on dark transitions | Normal on VA, a discount on anything sold as fast |
| Thirty thousand hours or more on the clock | The backlight has dimmed; price it as old |
| Ghosting at speed | Discount on a monitor sold for gaming, otherwise minor |
| One dead input | Discount, unless it is the one you need |
The mistake almost everyone makes
Testing in a bright room. Bleed, black uniformity and low-level detail are all invisible under normal lighting, which is exactly why a seller can honestly believe a monitor is flawless. If you cannot darken the room, at least cup your hands around the edges of the screen while the black test runs — it is enough to see the difference.
Common questions
What is worth walking away from?
A dead pixel in the middle of the screen, and any picture that changes when you press the frame. The first cannot be fixed and you will see it every day; the second is an internal fault that will get worse. Bleed, tint and a tired overdrive setting are all things to pay less for rather than reasons to leave.
The seller is getting impatient. Which three tests if that is all I get?
Pixels, bleed and the bezel press. The first two are the faults that cannot be repaired and are invisible on a wallpaper, and the third is the one that turns a bargain into a repair. Everything else on the list either has a fix you can apply yourself afterwards, or affects the price rather than the decision. Two minutes covers all three if you have the tabs already open, which is the real argument for opening them before you arrive.
The seller has no computer to plug it into.
Then you cannot check it, and no amount of looking at a powered-off screen substitutes. Bring a laptop. Every test here runs in a browser, so a laptop and a cable are the entire kit.
How much bleed is too much?
The practical test is whether you can see it in normal room lighting on ordinary content — not on a black screen in the dark, where every monitor ever made shows some. If it is visible during a film with a lamp on, it is too much.
Does burn-in apply here?
On an LCD, no — what looks like burn-in is usually temporary image retention that clears. On an OLED it is permanent and worth checking specifically: a solid grey field will show it as faint outlines of whatever was left on screen for months.
Is a monitor with a stuck pixel worth trying to fix?
It costs ten minutes to try, and it works on stuck pixels rather than dead ones. Do the fixing after you have used the fault to negotiate, not before.