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Why Does My Overhead Projector Keep Blowing Lamps?

Over the past 25 years I have had the unique opportunity to talk directly with many of the professionals and instructors who use Overhead Projectors as an integral part of their profession. The stories they have shared with me have given me direct insight to some of the most common problems experienced by owners of today’s and yesterday’s Overhead Projectors.

I would like to share this unique compilation of information with a series of articles derived directly from some of the most common questions and complaints that I receive from my clients in the Audio Visual Industry.

The first thing that comes to my mind is the question that I am asked almost every day; “My Overhead Projector keeps blowing lamps, what could be the problem?”

Most of today’s Overhead Projectors use projection lamps that require 82 volts to operate. Because the AC outlet that you plug your Overhead Projector into is 120 volts, a special electronic component is required to create the 82 volts needed to operate the projection lamp. This electronic component is called a diode (rectifier).

When the diode (rectifier) of your Overhead Projector becomes defective, it allows the line voltage of 120 volts to go directly to the 82 volt lamp. This additional voltage is too much for the projection lamp to handle, when the user turns the overhead projector on, the projection lamp will burn out in a matter of seconds due to this excessive voltage. In some cases the end user will place several new lamps into the Overhead Projector before they realize that the problem is not a defective projection lamp.

If you have a basic knowledge of Electronics or basic wiring the diode is something that most end users can replace themselves, otherwise this problem should be handled by a professional service technician.