Dots that sit in exactly the same spot no matter what you project — white specks on dark scenes, black ones on bright — are not dust on the lens and not a setting you can change. They are mirrors on the DMD chip that have stopped moving, and no amount of cleaning brings them back.
How to tell it is the DMD chip
Five things separate dead mirrors from everything else that puts marks on a picture:
- They never move. Pan the image, change the source, move the projector — the dots stay at the same coordinates on screen.
- They show on the projector’s own menu. The menu is generated inside the projector, so if the dots are there too, nothing outside the machine is causing them.
- They are pixel-sharp. Dust on the lens is soft and blurry and shifts as you change focus. A dead mirror is a hard-edged square.
- They are white on dark, or black on bright. Which way round depends on the angle the mirror stuck at.
- They multiply slowly. Most people notice one or two, then a dozen a few months later.
What a DMD chip is, and why mirrors die
A DLP projector builds its picture on a single chip carrying one hinged micro-mirror per pixel — hundreds of thousands of them on an older machine, several million on a 4K one. Each mirror tilts a few thousand times a second, throwing light either into the lens or into a light trap. That is the whole image: a field of mirrors flickering in formation.
A mirror that stops tilting is a pixel stuck on or stuck off, permanently. Heat cycling is the usual reason — every warm-up and cool-down works the hinge — helped along by dust that has found its way into the optical path, and by any sharp knock the projector has taken. It is wear, not a defect, and it is why a projector with thousands of hours on it starts to freckle.
Check these first, before you spend anything
- Look at the menu. Unplug every source and open the projector’s own menu. Dots still there? The chip. Dots gone? The fault is in your source, cable or player.
- Change the input and the cable. A failing HDMI board or a bad cable can put fixed artefacts on screen that look similar.
- Refocus. If the marks blur as you rack focus, they are on the lens or in front of it — a clean may be all you need.
Can it be repaired?
Yes. The DMD is a replaceable part, not a write-off. The job is to open the light engine, separate the chip from its heatsink and prism assembly, fit a matched replacement and realign the optical block.
It is not a kitchen-table repair. The prism assembly is open while the work is done, and a single speck of dust that settles inside it will be projected, in focus, for the rest of the projector’s life. That is the real reason this one goes on a bench rather than into a DIY afternoon.
Is it worth doing?
Honestly, sometimes not. A handful of dots near the edge of the picture on a projector you watch films on will take a long time to become a nuisance, and you may prefer to live with them. Dots across the middle of the frame, or any dots at all on a machine you present with, are a different matter.
We refurbish and sell these projectors as well as repair them, so we know what a given model is worth against what the work would cost — and if replacing it is the better answer, that is what the diagnosis will say.