Heathkit IT-5283 - Page 3

=
strong station, and the probe is connected, a signal
should be present at the rod antenna, the tuning
capacitor, and G1 of FET Q2. On sameradios, the hum
overrides the signal, which makes it necessary to
move the probe to the 1st IF stage (base of transistor
Q3}. in order to check the operation of the first slage.
You can trace the path of the signal through the suc-
ceeding IF stages to the detector. During these tests,
you can estimate the gain per stag
gain that can be expected
determined by reference to manufacturer's specifica-
tions or by previous experience in making similar
tests.
In some cases the RF probe causes a slight detuning.
effect when you apply it to tuned circuits. In these
cases, advance the tes! probe ta the next test point. Ifa
aod cignal is pracunt, it is reasonable to assume that
the preceding stage is functioning properly.
You can use the same general procedure in checking,
RF and IF stages in TV and FM circuits. Since the
actual signal is most important, the Signal Tracer will
detect the presence ar absence of the signal regardless
of the type of circuit involved.
AUDIO SIGNAL TRACING
Alter the signal has gune through thedetector (diode
D1) in the radio, the RF probeis not required. Turn the
probe switch to the DC position. Hereagain, the same
general conditions apply as described previously.
After the detector stage, you can trace the signal
through the audio stages (transistors Q6,Q7, Qa, and
Q9). to the speaker. These tests can be made quickly
and easily and any circuit fault will be indicated by a
loss of gain or signal in succeeding stages. You can
also spot intermittent or faulty volume controls or
coupling capacitors. When you use the Signal Tracer,
keep in mind that it will detect the presence as well as
the absence of a signal. For example, it is common
practice to use a high capacity by-pass capacitor in
the audio output circuit. If the capacitor is open, there
Page 33
will bea definite indication of a signal at the by-pass
capacitor. whereas a good capacitar will pass the sig-
nal to ground in the desired manner.
signal will be very high, so reduce the |
on the Signal Tracer.
TEST SPEAKER
In
service
work,
it
is
sometimes
necessary
to
take
the
chassis
of
a
radia
or
TV
to
the
repair
shop
to
complete
the
repair
work.
In
many
instances,
the
speaker
is
separate,
and
may
he
rather
inaccessible.
The
circuit
may
specify
a
permanent
magnet
type
speaker.
If
so,
you
can
substitute
the
Signal
Tracer’s
speaker
in
those
cases.
When
the
FUNCTION
switch
is
in
the
OFF/SPKR
SUB
position,
the
speaker
in
the
Signal
‘Traver
is
disuunuectad
from
the
tracer
circuitry
and
connected
to
the
front
panel
jacks.
Thus,
the
radio
or
‘TV
speaker
wires
are
connected
directly
to
these
jacks,
This
feature
eliminates
the
need
to
remove
and
reinstall
the
speaker
on
every
service
job.
AUDIO SYSTEMS
Quite frequently. service technicians may service au-
tomatic record changers or phano mechanisms.
When mechanical repairs or adjustments are made on
the changer mechanism, they may want to check the
output of the phono cartridge. By connecting the
INPUT of the Signal Tracer to the output of the record.
changer. the changer's output can be heard in the
speaker of the Signal Tracer. Any irregularity in
mechanical operation, such as turntable wow or
thump. of any objectionable noise that could be
transmitted through the phono cartridge and repro-
duced as an undesirable condition. will be heard in
the Signal Traces’s speaker.
You can also use the same procedure in checking
microphones and musical instrument pickups. Gen-
erally the Signal Tracer will check any equipment
which requires an audio system.