8.4.12 Adjust the first, second and third i-f trans-
former circuits as outlined by the manufac-
turer. In some instances the procedure will
give three reference markers, usually 42.17
MHz, 45.75 MHz and a 44 MHz sweep center
frequency marker.
If no order of adjustment
is given, keep in mind that the output circuit
of the first i-f amplifier adjusts the response
of the
i-f with respect to the 45.75 MHz mark-
er and that the output coil of the second i-f
amplifier adjusts the response of the
i-f curve
with respect to the 42.17 MHz marker. The
output coil of the third i-f amplifier is tuned
to the center of the passband and is adjusted
for tilt correction. Be sure that the proper slug
is adjusted in the third i-f transformer, be-
cause one coil performs the i-f tilt correction
and the other coil is the sound trap adjust-
ment (41.25
MHz).
NOTE
In many procedures the term or phrase "Set
the marker height ...
" is used extensively
when doing alignment work. This phrase
may be misleading because, actually, the
marker height on the response curve is not
adjustable. The marker is simply a reference
frequency which is independent of response
amplitude or sweep width. In fact, without a
response curve observed on the oscilloscope,
the markers, being post injected, are still
visible on the oscilloscope base line. When
the term (Set the marker height) is used,
actually what is being performed is that the
response of the i-f stage is being adjusted so
that at a particular marker frequency the
response is at some percentage down from
the maximum. For example, when the oper-
ator is instructed to set the height of the
(42.17 MHz) marker at 50% amplitude on the
i-f response curve by adjustment of the sec-
ond i-f transformer, actually what is being
done is this: The second i-f transformer is
adjusted to alter the i-f response curve so
that at 42.17 MHz the response is 50% of
maximum.
8.4.13 After completion of the i-f alignment, recheck
the position of the sound marker, especially
if pronounced readjustment of the third i-f
transformer or coil has been required to re-
store proper alignment.
8.4.14 After obtaining the desired i-f response so
that the 42.17 MHz marker and the 45.75 MHz
markers are located as specified, turn on the
41.67 MHz marker and the 42.67 MHz marker.
These markers, together with the 42.17 MHz
marker, define the response portion of the i-f
curve on which the chroma information is
carried. The marker should be positioned as
indicated in the manufacturer's response
curve drawings. The i-f alignment instruc-
tions outlined here apply whether the signal
is injected at the mixer test point or at the
antenna terminals.
8.5
CHROMA CIRCUIT ALIGNMENT
8.5.1 Upon completion of the i-f alignment, recheck
the chroma alignment section of the manufac-
turer's procedure and verify that the
biases
are properly set and that the demodulator
probe (PR-151) is properly connected.
8.5.2
BANDPASS AMPLIFIER ALIGNMENT USING
DIRECT VIDEO SWEEP
8.5.2.1 Place the FUNCTION switch of the Model 415
to the VIDEO position. Set the ATTENUA-
TOR control to minimum. Connect r-f cable
to specified injection point.
8.5.2.2 Turn on the SOUND (41.25/4.5 MHz) marker
and the three CHROMA markers (41.67 /4.08,
MHz, 42.17 /3.58 MHz and 42.67 /3.08 MHz).
8.5.2.3 Using the SWEEP WIDTH control and the
CENTER FREQUENCY control reduce sweep
width and center as required so that the
sound and chroma markers occupy approxi-
mately 70 per cent of the total oscilloscope
sweep.
8.5.2.4 Place the PROBES switch in the DEMOD
position.
8.5.2.5 Adjust the ATTENUATOR control for the
specified peak-to-peak amplitude as ob-
served on the oscilloscope.
8.5.2.6 Adjust the bandpass transformer as required
to obtain the desired overall response. Nor-
mally the bandpass transformer consists of
two tuning adjustments. One of the tuning
slugs adjusts the band width of the trans-
former and the other adjusts the center fre-
quency of the transformer. The bandwidth
adjustment is used to position the 3.08
MHz
and 4.08 MHz markers on the curve and the
tuning adjustment performs the tilt adjust-
ment as required.
Direct video sweep alignment is done prior
to performing final adjustment of the chroma
tuned circuits using video sweep modulation
or an equivalent method. Upon completion
of the chroma prealignment overall chroma
circuit alignment is performed by injecting
either at the mixer test point or at the antenna
terminals (Section 8.5.3).
8.5.2.7 Remove the r-f cable from the input to
,the
chroma bandpass amplifier.
8.5.3
CHROMA ALIGNMENT USING SIGNAL
INJECTION AT THE ANTENNA TERMINALS
OF THE RECEIVER OR AT THE MIXER
TEST POINTS
Chroma alignment is usually performed by
either of these methods. The obvious advan-
tage is that once all probes and biases have
been connected to the television receiver the
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