8.0
COMPLETE 1-F AND CHROMA ALIGNMENT
8.1.8
Perform the trap alignment by selecting one
PROCEDURE USING THE MODEL 415
marker frequency at a time and adjusting the
415 ATTENUATOR to obtain an indication at
The set-up instructions of Par. 5.2 and Figure
the video detector test point.
A recovered
5.2 should also be used in this section. 400 hz sine wave will be observed on the os-
Much of the alignment touch-up procedure
cilloscope. The 400 hz modulation is not
information outlined in Section 7.3 and the
synchronized to the sweep voltage and, there-
trap adjustment information of Section 7.2 is
fore, may not be stationery on the oscillo-
also applicable in the complete i-f and chro-
scope trace. Keep the ATTENUATOR level as
ma alignment procedures. Some of the infor-
low as possible while still maintaining a us-
mation will be repeated in this section to
able level on the oscilloscope. The oscillo-
maintain the continuity of the instructions.
scope may be used at maximum gain to
Read the general alignment information of
increase the overall sensitivity of the measur-
Section 6.3 for additional background infor-
ing system. Trap circuits are always aligned
mation, if you have not already done so.
for a minimum indication as observed on the
oscilloscope.
8.1
TRAP ALIGNMENT USING
8.1.9
Repeat the procedure of the preceding step
MODULATED MARKERS
for alignment of all specified trap frequency
8.1.l
Determine the injection point for introducing
circuits. Usually one or two of the trap fre-
quency adjustments involve the adjustment
spot frequency markers into the i-f. This in-
of a tuned circuit and a potentiometer.
jection point is usually a mixer test point and
is indicated on the tuner drawing or photo-
Both the coil and potentiometer are alternate-
graph.
ly adjusted for minimum oscilloscope indica-
tion. Remember that the potentiometer must
8.1.2
Determine from the alignment instructions
not be adjusted to either extreme of its ad-
the frequency and number of traps to be
justment range.
prealigned. The standard trap frequencies
Upon completion of trap alignment tum off
are the adjacent pix carrier (39.75 MHz), the
all markers.
sound carrier (41.25 MHz) and the adjacent
sound carrier (47.25 MHz). Several manufac-
8.2
PRE-ALIGNMENT OF 1-F BANDPASS COILS
turers have an additional trap frequency
AND TRANSFORMERS (When Specified)
over and above those listed here. For exam-
pie, some Motorola receivers have a trap
Some alignment procedures specify a pre-
frequency at 35.25 MHz and some Philco re-
tuning of all i-f bandpass coils and transform-
ceivers have a trap frequency at 38.75 MHz.
ers as well as the traps as previously out-
Determine the location of the trap circuit,
lined. The procedure is identical to the trap
both physically on the television chassis as
adjustment except that in this case each cir-
well as the location on the schematic dia-
cuit is tuned for a maximum output as indi-
gram. All traps excepting the sound trap
cated on the oscilloscope using modulated
(41.25
MHz) are located at the input to the
markers. Once again, remember that only
first i-f amplifier.
one marker at a time may be used. Always
turn off the marker when alignment of the
The sound trap circuit is usually located in
particular coil or transformer is complete.
the last i-f transformer or in the output circuit
of the last i-f stage.
8.3
TUNER LINK ALIGNMENT (When Specified)
8.1.3 Locate the bias points and preset the bias
8.3.l Turn off the television receiver.
supplies of the Model 415 to specified values
making sure that the polarities are correct.
8.3.2 Connect the load block provided with the
Model 415 accessories between the plate of
8.1.4
Connect the bias leads to the required bias
the first i-f amplifier and ground with the ca-
points and recheck the bias values using the pacitor at the plate end and the resistor at
VTVM.
the ground end. Connect the second load
block between plate and ground of the sec-
8.1.5
Turn off all markers of the Model 415 and
ond i-f amplifier in a similar manner.
place the FUNCTION switch in the MOD
MKR position.
8.3.3 Connect the PR-151 Demodulator Probe to the
junction of the resistor and capacitor of the
8.1.6
Connect the output cable of the Model 415 to
first load block and connect the black lead
the signal injection point of the tuner.
of the probe to ground. Connect the PR-151
cable to the DEMOD PROBE jack of the
8.1.7
Connect the direct cable of the 415 to the
Model 415. Place the PROBES switch in the
video detector test point. A IOK-ohm resistor
DEMOD position.
is provided in the
"hot" lead of the direct
8.3.4 Set the FUNCTION switch of the 415 to the
cable. The !OK-ohm resistor specified in align-
I-F position. Set the SWEEP WIDTH control
ment procedures for isolation is not required. to maximum (fully clockwise.)
58
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