What the boardroom saw: a growing dark patch
Short answer: A corporate NEC DLP projector developed a black blob approximately 8 cm in diameter on a 2.5-metre screen during a board meeting. The fault was a cluster of stuck-off DMD (Digital Micromirror Device) pixels. The chip was replaced; the projector returned to full image quality. The decision to repair rather than replace was clear once the projector's replacement value was established.
The customer described the fault precisely: a dark oval region in the lower-right quadrant of the screen that appeared mid-presentation, did not move, did not shift when they changed the input source, and did not go away when they turned the projector off and back on. Each of those details is diagnostic information. A dust spot or condensation on the lens would shift slightly with zoom. A lamp fault would affect overall brightness, not create a localized black region. A fixed localized dark region that is independent of input and zoom points to one thing in a DLP projector: the DMD chip.
Understanding the DMD fault
What the DMD chip is
The DMD (Digital Micromirror Device), developed by Texas Instruments, is the core imaging component of a DLP projector. It is a silicon chip containing millions of microscopic aluminium mirrors — one per pixel — each approximately 7.6 microns wide (smaller than a human red blood cell). Each mirror tilts on a hinge between two positions: one reflecting light through the lens (producing a bright pixel) and one reflecting it into a light absorber (producing a dark pixel). The image is formed by rapidly switching each mirror thousands of times per second — the ratio of on-time to off-time determines each pixel's brightness.
When the hinge mechanism of a mirror group fatigues or sticks — a failure mode that increases with age and heat cycling — those mirrors remain locked in the off position regardless of the signal. The result is a region of permanently dark pixels: the black blob.
Confirming the fault versus dust contamination
Before the chip was condemned, the bench team confirmed that the fault was in the DMD and not on the optical path. The procedure: remove the lens, shine a collimated light source directly onto the DMD from the front (the projection direction), and observe the reflection with the chip powered. Stuck-off mirrors show as a non-reflecting dark region. Dust on a mirror or the optical block shows as a shadow with soft edges that moves when the dust is disturbed. In this case, the dark region had sharp pixel-grid edges and was completely fixed — confirmed DMD fault, not dust.
Repair vs replace
The NEC projector in question was a mid-range commercial model with a replacement value of approximately ₹65,000 for an equivalent current unit. DMD chip sourcing for this model produced a refurbished chip at ₹8,500. Labour for BGA desoldering (removing the old chip from its solder balls using a hot-air rework station) and re-soldering: ₹2,200. Post-repair image calibration: included. Total: ₹10,700 — approximately 16% of replacement cost. An easy repair decision.
The contrast situation is a DLP projector in the ₹25,000 to ₹30,000 purchase price range where a DMD chip plus labour approaches ₹15,000 or ₹18,000. In those cases, the repair cost as a percentage of replacement cost is over 50%, and the bench team will flag this clearly. For more on the cost landscape, our guide to projector DLP chip repair has current ranges by model category. For the general framework on when to repair versus replace, the 12-year-old Epson recap story covers the decision criteria from a different angle. WhatsApp model and fault description to 7702503336 for a same-day diagnosis in Hyderabad.