Trio CS-1566A, Инструкция по эксплуатации

Страница: 22 / 34

Sync Pulse Analysis:
The IF amplifier response of a television receiver
can be evaluated to some extent by careful
observation of the horizontal sync pulse waveform.
The appearance of the sync pulse waveform is
affected by the I F amplifier bandpass c h a -
racteristics. Some typical waveform symptoms
and their relation to IF amplifier response are
indicated in F i g . 2 1 . Sync pulse waveform
distortions produced by positive or negative
limitting in IF overload conditions are shown in F i g .
22.
Fig. 21 Analysis of sync pulse distortion
N O R M A L S Y N C P U L S E
S Y N C P U L S E C O M P R E S S I O N
C A U S E D B Y L I M I T I N G
" W H I T E " S A T U R A T I O N
C A U S E D B Y L I M I T I N G
FM R E C E I V E R A D J U S T M E N T S
1. Connect a sweep generator to the mixer input
of the FM receiver. Set the sweep generator
for a 10.7 MHz centered sweep.
2. Connect the sweep voltage output of the
sweep generator to the C H 2 input jack of the
oscilloscope and set the oscilloscope controls
for X - Y operation ( S W E E P T I M E / D I V to X - Y ) .
3. Connect the vertical input probe to the
demodulator input of the FM receiver.
4. Adjust the oscilloscope vertical and horizontal
gain controls for a display similar to that
shown in Fig. 23A.
5. Set the marker generator precisely to 10.7
MHz. The marker "pip" should be in the
center of the bandpass.
6. Align the IF amplifiers according to the ma-
nufacturer's specifications.
7. Move the probe to the demodulator output.
The " S " curve should be displayed, and the
10.7 MHz "pip" should appear exactly in the
center (see Fig. 23B).
Adjust the demodulator according to the ma-
nufacturer's instructions so the marker moves
an equal distance from the center as the
marker frequency is increased and decreased
an equal amount from the 10.7 MHz center
frequency.
22
Fig. 2 2 Sync pulse waveforms
C I R C U I T
D E F E C T
H O R I Z O N T A L
P U L S E
D I S T O R T I O N
O V E R A L L R E C E I V E R
F R E Q U E N C Y R E S P O N S E
E F F E C T O N
P I C T U R E
N O R M A L
C I R C U I T
P I C T U R E
N O R M A L
L O S S O F H I G H
F R E Q U E N C Y
R E S P O N S E
L O S S O F P I C -
T U R E D E T A I L
E X C E S S I V E H I G H
F R E Q U E N C Y R E
S P O N S E N O N
L I N E A R P H A S E
S H I F T
F I N E V E R T I C A L
B L A C K A N D W H I T E
S T R I A T I O N S F O L -
L O W I N G A S H A R P
C H A N G E I N P I C
T U R E S H A D I N G
L O S S O F L O W
F R E Q U E N C Y
R E S P O N S E
C H A N G E I N S H A
D I N G O F L A R G E
P I C T U R E A R E A S .
S M E A R E D P I C
T U R E