Member Avatar for thepastimer

I have this old CRT monitor that has a dead pixel. At first it was no concern because, hey, its old. But then I noticed that it wasn't always in the same spot, which perplexed me. It moves along the vertical axis, but never on the horizontal axis. Does anyone know what might cause this? I'm leaning toward the pin cushion, but I don't know for sure.

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Dani AI

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A short expert addendum that expands on points from and and gives a few safe, practical checks plus what each outcome usually means.

Try these non‑destructive checks first:

  • Clean the front glass with a soft cloth and mild cleaner, then re‑inspect. External smudges or residue are the cheapest fixes.
  • Do a simple parallax test: hold a thin object (pencil, finger) a few centimetres from the screen and move your head side to side. If the dark spot moves relative to the image but not relative to the object, the defect is on or very near the glass; if it stays fixed to the picture, it’s inside the tube.
  • Show full‑screen solid colours (white, red, green, blue). A spot that is visible on all colours and stays the same tone usually points to a physical mask/phosphor/emission fault rather than a video‑signal glitch.
  • Photograph the area with a steady hand or tripod (no flash). If the spot appears in the photo in the same place, it’s not a simple reflection.

How to read the results and next steps:

  • External dirt or marks: clean thoroughly and keep using.
  • Internal shadow‑mask contamination, localized phosphor wear, or an electron‑gun emission fault: these are internal tube problems. Internal cleaning/repair requires discharging the tube and accessing high‑voltage parts, so it’s a job for a qualified CRT technician. Degaussing can fix magnetization/geometry issues but won’t remove physical contamination or burned phosphors; see the background on degaussing and shadow masks for details (Degaussing, Shadow mask, Aperture grille).

Safety note: CRTs contain lethal voltages even when unplugged. Do not attempt tube disassembly or anode discharge at home; refer repair work to professionals or consider replacement as the usual cost‑effective choice (Cathode‑ray tube hazards).

Recommended Answers

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Member Avatar for Suspishio

A moving "dead pixel" must be due to the video circuitry and not the CRT. You might care to tell us which video card you have. It contains a frame buffer and if this is not populated correctly, neither will your CRT screen.

Member Avatar for Salem

> It moves along the vertical axis, but never on the horizontal axis
By itself, or when you scroll a page or a window or ...

Member Avatar for thepastimer

Suspishio: The dead pixel is there even when the monitor is not plugged into any computer. The graphics card its plugged into is a nvidia GeForce 8500 GT.
Salem: The pixel will never move while the monitor is on, but every time it gets turned on the pixel is in a different position on the vertical axis, although it only ever moves half an inch.

Thanks for replying.
By the way, I looked at it with a magnifying glass; its not completely dead, just very dark.

Member Avatar for Suspishio

Ah - that's a whole different picture (forgive the pun!).

What follows is logical deduction rather than a definite answer. If the dead spot is definitely in a different position then it could be dirt on the shadow mask that lets the electrons hit the phosphor dots.

That might hold if the dead spot moves to and stays at another positionwhen the screen has warmed up.

Does this move occur only after a long switch off period?

Regarding your pin-cushion theory, you'd notice that at the edges, surely. A dead pixel wouldn't move - it's a physical piece of phosphor; the shadow mask would send electrons to positions determined by the pin-cushion effect and, yes, if it's a transient faukt in monitor circuitry, coupled with a shadow mask blockage, I can see a black spot moving.

Either way, it now seems that the monitor is going home.

Member Avatar for thepastimer

The occurrence of the pixel moving is rather erratic though it does seem to move after the monitor has been cold for about half a day. It only jumped once while the computer was on. One interesting thing is that the pixel perfectly aligns with the border of my browser when it is not maximized (which is how it is quite often).

Member Avatar for Suspishio

So what happens when you move the non-maximised browser window?

Member Avatar for Salem

As it's a CRT, have you tried pressing the degauss button recently (or at all?)

Member Avatar for thepastimer

The degauss button was the first thing i tried. It didn't help at all.
When the browser is not maximized, I can't see that the pixel is dead, but as soon as i move the browser, it shows up. Do you think it may have burned out just because its such a small space that has to be displayed black while the browser is not maximized (with the adjoining horizontal pixels being close to white)?

Member Avatar for Suspishio

The browser will minimise to the last place you moved it to. So a dead pixel in a particular position will appear in the same place.

I think we're going round in circles. You have a dead pixel - that's it.

Member Avatar for thepastimer

The pixel is dead no matter what I try. However, I am now almost certain its probably what you said earlier (about it being some dirt in the shadow mask) because I changed the size of the image displayed and the pixel stayed in the same spot. Its probably just time for a new monitor.

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