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. Through these interactions I have accumulated notes and information that has inspired me to write these articles that pertain to some of the most common problems experienced by owners of today's and yesterday's Overhead Projectors.
This is the third article in a series of articles that will be written from a professional Electronics Technicians point of view in regards to some of today's most common Overhead Projector problems.
A question that I am asked quite frequently is; "My Overhead Projector has no power, what could be causing the problem?"
This is not one of the most common problems we encounter, but it is still an issue that most users of Overhead Projectors will face one time or another. The cause of this problem is not as simple as detecting a defective lamp socket. There are several things to consider when there is no power to your Overhead Projector and I will take one step at a time.
Interlock switch: In order for you overhead projector to be UL Listed it must have what is refered to as a interlock switch. The interlock switch cuts off power to the projector when the lamp door or top cover are opened to access any of the components inside the case of the Overhead Projector, keeping you safe from any electricity. If this switch is defective it may cause you Overhead Projector to have the symptoms of now power.
Resistor: Some Overhead Projectors are equipped with a resistor in their electrical circuitry. The resistor is used sometimes in conjunction with a diode to drop the line voltage, or it may also be used on Overhead Projectors that have a Hi/Lo lamp function. If this resistor is defective it may also cause the symptoms of no power to your projector.
Safety Thermostat: The safety thermostat is an electrical device that is temperature sensitive. The sole purpose of this device is to protect your Overhead Projector from overheating and damaging expensive internal components like the Fresnel lens. If the projector overheats, this thermal device cuts off the flow of electricity to your projector. If this thermal device is defective is could also cause the symptom of no power to your Overhead Projector.
These are not all of the causes for loss of power in your projector, but are the most commonly seen. These types of problems should be left to a professional service technician because of the possible electrical hazards encountered when working with these types of electronic components.
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