20
Subject to change without notice
indicating range of the component tester is limited. The
impedance of the component under test is limited to a
range from 20
Ω
to 4.7k
Ω
. Below and above these values,
the test pattern shows only short-circuit or open-circuit.
For the interpretation of the displayed test pattern, these
limits should always be borne in mind. However, most
electronic components can normally be tested without
any restriction.
Using the Component Tester
The component tester is switched on by depressing the
COMP. TESTER
pushbutton (on) beneath the screen.
This makes the vertical preamplifier and the timebase
generator inoperative. A shortened horizontal trace will be
observed. It is not necessary to disconnect scope input
cables unless in-circuit measurements are to be carried
out. In the
COMP. TESTER
mode, the only controls which
can be operated are
INTENS.
,
FOCUS
, and
X-POS.
. All
other controls and settings have no influence on the test
operation.
For the component connection, two simple test leads
with 4mm Ø banana plugs, and with test prod, alligator clip
or sprung hook, are required. The test leads are connected
to the insulated socket and the adjacent ground socket
beneath the screen. The component can be connected to
the test leads either way round.
After use, to return the oscilloscope to normal operation,
release the
COMP. TESTER
pushbutton (off).
Test Procedure
Caution! Do not test any component in live circuitry
−−−−−
remove all grounds, power and signals connected
to the component under test. Set up Component
Tester as stated above. Connect test leads across
component to be tested. Observe oscilloscope display.
Only discharged capacitors should be tested!
Test Pattern Displays
Page M17 shows typical test patterns displayed by the
various components under test.
•
Open circuit is indicated by a straight horizontal
line.
•
Short circuit is shown by a straight vertical line.
Testing Resistors
If the test object has a linear ohmic resistance, both deflecting
voltages are in the same phase. The test pattern expected
from a resistor is therefore a sloping straight line. The angle
of slope is determined by the resistance of the resistor under
test. With high values of resistance, the slope will tend
towards the horizontal axis, and with low values, the slope
will move towards the vertical axis.
Values of resistance from
20
Ω
Ω
Ω
Ω
Ω
to
4.7k
Ω
Ω
Ω
Ω
Ω
can be approxi-
mately evaluated. The determination of actual values will
come with experience, or by direct comparison with a
component of a known value.
Testing Capacitors and Inductors
Capacitors and inductors cause a phase difference between
current and voltage, and therefore between the X and Y
deflection, giving an ellipse-shaped display. The position
and opening width of the ellipse will vary according to the
impedance value (at 50Hz) of the component under test.
A horizontal ellipse indicates a high impedance or a
relatively small capacitance or a relatively high
inductance.
A vertical ellipse indicates a small impedance or a
relatively large capacitance or a relatively small
inductance.
A sloping ellipse means that the component has a
considerable ohmic resistance in addition to its
reactance.
The values of capacitance of normal or electrolytic
capacitors from
0.1µF
to
1000µF
can be displayed and
approximate values obtained. More precise measurement
can be obtained in a smaller range by comparing the
capacitor under test with a capacitor of known value.
Inductive components (coils, transformers) can also be
tested. The determination of the value of inductance
needs some experience, because inductors have usually
a higher ohmic series resistance. However, the impedance
value (at 50Hz) of an inductor in the range from 20
Ω
to
4.7k
Ω
can easily be obtained or compared.
Testing Semiconductors
Most semiconductor devices, such as diodes, Z-diodes,
transistors, FETs can be tested. The test pattern displays
vary according to the component type as shown in the
figures below.
The main characteristic displayed during semiconductor
testing is the voltage dependent knee caused by the
junction changing from the conducting state to the non
conducting state. It should be noted that both the forward
and the reverse characteristic are displayed simultaneously.
This is a two-terminal test, therefore testing of transistor
amplification is not possible, but testing of a single junction
is easily and quickly possible. Since the test voltage
applied is only very low, all sections of most semi-
conductors can be tested without damage. However,
checking the breakdown or reverse voltage of high voltage
semiconductors is not possible. More important is testing
components for open or short-circuit, which from
