31
Subject to change without notice
Adjustments
The polarity of an unknown diode can be identified by
comparison with a known diode.
Testing Transistors
Three different tests can be made to transistors: base-
emitter, base-collector and emitter-collector. The resulting
test patterns are shown below. The basic equivalent circuit of
a transistor is a Z-diode between base and emitter and a
normal diode with reverse polarity between base and collector
in series connection. There are three different test patterns:
For a transistor the figures b-e and b-c are important. The
figure e-c can vary; but a vertical line only shows short circuit
condition.
These transistor test patterns are valid in most cases, but
there are exceptions to the rule (e.g. Darlington, FETs). With
the
COMPONENT TESTER
, the distinction between a P-N-P
to an N-P-N transistor is discernible. In case of doubt,
comparison with a known type is helpful. It should be noted
that the same socket connection (
COMP. TESTER
or ground)
for the same terminal is then absolutely necessary. A
connection inversion effects a rotation of the test pattern by
180 degrees round about the center point of the scope
graticule.
Pay attention to the usual caution with single MOS-
components relating to static discharge or frictional
electricity!
In-Circuit Tests
Caution!
During in-circuit tests make sure the circuit is dead. No
power from mains/line or battery and no signal inputs
are permitted. Remove all ground connections including
Safety Earth (pull out power plug from outlet). Remove
all measuring cables including probes between
oscilloscope and circuit under test. Otherwise both
COMPONENT TESTER leads are not isolated against
the circuit under test.
In-circuit tests are possible in many cases. However, they are
not well defined. This is caused by a shunt connection of real
or complex impedance - especially if they are of relatively low
impedance at 50Hz - to the component under test, often
results differ greatly when compared with single components.
In case of doubt, one component terminal may be unsoldered.
This terminal should then not be connected to the ground
socket avoiding hum distortion of the test pattern.
Another way is a test pattern comparison to an identical circuit
which is known to be operational (likewise without power and
any external connections). Using the test prods, identical test
points in each circuit can be checked, and a defect can be
determined quickly and easily. Possibly the device itself under
test contains a reference circuit (e.g. a second stereo channel,
push-pull amplifier, symmetrical bridge circuit), which is not
defective.
Adjustments
As described in the
“Menu”
section, the instrument`s
software contains the submenu
“CALIBRATE”
. The controls
regarding the menus are described under item
MENU (34)
in
section “Controls and Readout”. After a warm up time of 20
minutes, the following items can be used by operators not
equipped with precision instruments.
Both items are regarding the instrument’s temperature
response under extreme environmental conditions. Similar
effects can be caused by component failures as a result of
the application of too high voltage at an input and therefore
cannot
be compensated by the automatic adjustment
procedure. During these automatic adjustments there must
be no signal applied to any input.
