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
referred 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
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.
Mark Boehm is the president of M-B Electronics
[http://www.mbelectronics.com] He has over 25 years of experience in the
Audio Visual and Electronics Industry. You can contact M-B Electronics
[http://www.mbelectronics.com] at 800-872-9456 or at :email@example.com
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