Elenco Electronics EP-130, Manual

Page: 137 / 160

This circuit emits a sound if the material you are
checking conducts electricity. This is convenient
when you are looking at wires, terminals, or other
things and cannot look at a signal lamp or LED. Your
ears detect the results of the test while your eyes are
busy.
If the circuit that you are testing conducts electricity,
it will complete a voltage supply connection to a
standard pulse-type oscillator that uses a sensitive
PNP transistor. This tester can check almost any
component on the board. When testing the diodes
and transistors, remember that electricity only flows
in one direction through them (unless they have been
damaged).
If you look at the schematic, you will see that the
output from the transistor goes through the
transformer to the 0.02
μ
F capacitor and then to the
base of the transistor. The emitter of the transistor is
connected to the TEST terminal. When something
that allows electricity to flow is connected to the
terminal, the transistor starts to oscillate.
You can safely check almost any component with this
continuity checker because it carries a very low
current of about 15mA or less. You may want to try
measuring the continuity of pencil lines on paper,
water, metallic surfaces, and many other things.
Notes:
EXPERIMENT #115: AURAL CONTINUITY TESTER
-137-
Schematic
Wiring Sequence:
o
1-29
o
2-30
o
3-103-109
o
4-87-120
o
5-110-41
o
88-104-40
o
42-116-PROBES
o
115-131-PROBES
o
119-132