Zenith 19M20 Manual page 10

ALIGNMENT INSTRUCTIONS (cont)
HF AND MIXER ALIGNMENT
Remove the bias supply from C31 and connect a jumper from the tuner AGC lead (yellow) to chassis.
Connect the synchronized sweep voltage from the sweep generator to the horizontal input of the oscilloscope for horizontal deflection.
The sweep generator output lead should be terminated with its characteristic impedance, usually 50 ohms.
DUMMY
ANTENNA
Two 120S2
Carbon
Resistors
SWEEP
GENERATOR
COUPLING
Across antenna ter-
minals with 120S2 in
each lead.
SWEEP
GENERATOR
FREQUENCY
69MC
(10MC Swp)
201MC
(10MC Swp)
MARKER
GENERATOR
FREQUENCY
67.25MC
71.75MC
199.25MC
203.75MC
CHANNEL
4
11
CONNECT
SCOPE
Vert. Amp. thru
10KS3 to point ^> .
Low side to chassis.
ADJUST
A23,
A24,
A25
A26,
A27,
A28
REMARKS
Adjust for response similar to Fig. 5.
Adjust A26 and A27 for symmetrical
response similar to Fig. 6. Adjust A28
for proper band width. Repeat steps 5
and 6 until best overall symmetrical
response is obtained. Remove jumper
from tuner AGC terminal to chassis.
SOUND IF ALIGNMENT
Connect an attenuator {Zenith part #3-17203 or equivalent) in series with the receiver antenna.
Tune in a tone modulated TV signal and adjust the attenuator until the signal falls below the limiting level of the 6BN6 limiter detector, as
evidenced by a hiss similar to superregeneration.
Adjust the sound take-off transformer (A29, A30) the sound IF transformer (A31) and the quadrature coil (A32) for maximum sound of best
quality.
Adjust the buzz control (R9) for minimum intercarrier buzz.
II the intercarrier buzz cannot be eliminated with the buzz control check the setting of the AGC delay control adjustment.
II during the sound IF alignment the signal rises above the limiting level (hiss disappears) increase the attenuation until the hiss returns.
UHF TUNER ALIGNMENT
7.
8.
9.
Alignment of the UHF tuner should not be attempted unless proper test equipment is available.
Switch the receiver to the UHF position .
Connect the negative lead of a 2 volt bias supply to the ungrounded side of C31. Connect the positive lead to chassis.
Adjust the sweep generator output to provide 3 volts peak to peak on scope,
Connect the synchronized sweep voltage from the sweep generator to the horizontal input of the oscilloscope for horizontal deflection.
The sweep generator output lead should be terminated with its characteristic impedance, usually 50 ohms.
DUMMY
ANTENNA
Fig. 8
SWEEP
GENERATOR
COUPLING
Across UHF antenna
terminals thru
matching network (Fig.
8).
SWEEP
GENERATOR
FREQUENCY
713MC
(10MC Swp)
473MC
887MC
(10MC Swp)
MARKER
GENERATOR
FREQUENCY
711.25MC
471.25MC
885.25MC
CHANNEL
54
14
83
CONNECT
SCOPE
Vert. Amp. thru
IOKSI to point <$> .
Low side to chassis.
ADJUST
A33.A34,
A3 5
A36, A37
A38
REMARKS
Tuner rocket arm should be in the horizontal
position. If necessary, loosen set screw and
adjust tuner shaft so that rocker arm is
horizontal when the channel indicator is set
to channel 54. Do not adjust A33 unless
oscillator calibration is off more than
three channels. If necessary, adjust A33 to
place video market at 50% on response
curve as in Fig. 7, The image (weaker re-
sponse) will appear also. The response to-
ward the counter clockwise position of A33
is the correct response. Adjust A34 and
A35 for maximum amplitude and symmetry
of response similar to Fig* 7.
Check for response similar to Fig. 7. If
oscillator is off more than 3 channels
adjust the oscillator travel (osc., mixer and
ant, travel adjustments are the three round
thumb screws on top of tuner) adjustment to
scale. Care must be used in making this
adjustment so as not to move the rocker
arm out of its bearing. Set the mixer and
antenna travel adjustments for maximum
response on scope.
Adjust A36 to place video marker at 50% as
in Fig. 7. Adjust A37 and A38 for maximum
amplitude and symmetry of response similar
to Fig. 7.
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F I G . 5
F I G . 6
F I G . 7
\ON CONTINUOUS TUNER
F I G . 8
PAGE 7