7.2.9 Turn on ADJ SND (47.25 MHz) marker. Use the
level adjusting procedures of the preceding
paragraph to obtain a satisfactory indication
on the oscilloscope.
7.2.10 Tune the indicated adjacent sound (47.25 MHz)
trap coil on the receiver chassis. This adjust-
ment is usually located at the input circuit of
the first i-f stage. Sometimes a potentiometer
adjustment is specified together with the coil
adjustment, or a double tuned trap is used.
Alternately adjust for minimum indicated 400
Hz on the oscilloscope, using the minimum 415
output required to give a usable scope indica-
tion. Turn off ADJ SND (47.25 MHz) marker.
7.2.11 If an adjacent pix (39.75 MHz) trap adjustment
is included in the alignment instructions, per-
form the adjustment as in the preceding para-
graphs. The adjacent pix trap is usually lo-
cated at the first i-f stage input circuit. Turn
off the ADJ PIX (39.75 MHz) marker upon com-
pletion of the adjustment.
7.2.12 Place the FUNCTION switch of the 415 in the
IF position. Turn on the ADJ PIX (39.75
MHz)
and ADJ SND (47.25 MHz) markers. Set the
SWEEP WIDTH control to max. and center the
trace on the oscilloscope using the CENTER
FREQUENCY control. Adjust the ATTENUA-
TOR until the specified receiver i-f response
curve amplitude is obtained.
7.3.
1-F RESPONSE TILT ADJUSTMENT,
MIXER INJECTION
With the traps properly adjusted the remain-
ing touch-up should be in correcting excessive
tilt in the i-f response.
If the i-f sweep injection
point is at the mixer, the set-up connections of
the TRAP ADJUSTMENTS section can be
used. Proceed as follows:
7.3.l In the manufacturer's alignment procedure,
note which i-f coil is tuned to the center of the
i-f range (around
44 MHz). One of these is
usually specified as a tilt adjustment. Usually
the last i-f coil assembly combines the sound
(4I.25 MHz) trap adjustment and the tilt coil
adjustment. (Refer to Figure 6.5 of Section 6.2
for the effect of a center-tuned coil on overall
response of stagger-tuned circuits).
7.3.2 Observing the response pattern on the oscillo-
scope, adjust the coil which affects the tilt so
that the top of the i-f curve is horizontal.
7.3.3 Turn on the CHROMA (42.17) marker and the
PIX (45.75) marker. They should fall within the
tolerance limits specified in the alignment pro-
cedure. If they do not, proceed to the next step.
7.3.4 Additional tilt correction can be obtained by
minor adjustment of the i-f coils which affect
the height of the high-frequency and low-fre-
quency ends of the i-f response curve. These
are specified in either the spot frequency
alignment section or the overall sweep align-
ment section.
56
7.4.
CHROMA CIRCUIT ADJUSTMENT
The touch-up in this section is limited to tilt
correction of the chroma response.
7.4.1 With the i-f response obtained in Sec. 7.3
above, turn on the SOUND (41.25) and CHRO-
MA (41.67, 42.17, 42.67) markers and decrease
the sweep width, at the same time using the
CENTER FREQUENCY control to center the
four markers on the oscilloscope.
7.4.2 Place the CHROMA switch in the ON position
and recenter the oscilloscope trace
if required.
NOTE:
In performing adjustments in the chroma cir-
cuits, particularly the bandpass amplifier
transformer, the signal level at the video de-
tector is usually specified by the manufacturer.
Alignment procedures usually specify that the
level of signal injected at the mixer test point
be adjusted so that a certain
d-c voltage is
obtained at the video detector test point. This
level is set by using the
VTVM to monitor the
d-c level at the video detector test point while
adjusting the signal level applied to the mixer
input. With proper bias levels set in the i-f and
chroma circuits as specified by the manufac-
turer no further adjustment of signal levels
should be required to produce the proper
chroma level in the chroma portions of the
television receiver. Some procedures require
that the input level be adjusted to produce
a specified peak-to-peak waveform at the
chroma circuit test point, this usually being
the output of the bandpass amplifier.
If neither
a signal level or a peak-to-peak chroma re-
sponse amplitude is specified the following
must be done:
Observe the chroma response curve and ad-
just the signal input from the Model 415 so
that the amplitude of the chroma response
curve is centered in a range over which the
amplitude can be varied without distortion or
indications of overload.
7.4.3 Place the PROBES switch in the DEMOD posi-
tion and observe the chroma response curve.
7.4.4 Perform the indicated chroma circuit adjust-
ments to correct the curve tilt or to bring it
within tolerances. The tilt adjustment is usu-
ally one of the two slugs in the chroma band-
pass transformer of the television receiver.
7.5
TILT ADJUSTMENTS, ANTENNA INJECTION
If the specified signal injection point for i-f
alignment is not the mixer, the signal must be
injected at the antenna terminals.
7.5.1 Place the 415 FUNCTION switch in the CH 4
position.
7.5.2 CHROMA switch in OFF position.
7.5.3 Place the impedance switch of the r-f cable
terminating pad in the 300
Q position and con-
nect to the antenna terminals.
I
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