Sharp VC-780E - Page 31

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ee oe
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ADJUSTMENT
OF
Y/C
RECORDING
CIRCUIT
Adjustment
of
EE
level
Measuring
:
[ode
—*i
Rewarding
Input
signal
Standard
colour
bar
istair-case
waveform)
Video output terminal
Adjusting point R201 (EE level control)
Note:
The
video
output
terminal
should
be
terminated
with a 75-ohm impedance.
1. Set the unit to the record mode.
2.
Feed
the
colour
bar
signal
(stair-case
waveform}
to
the
video
input
terminal.
Observing
the
voltage
across
the
terminal
resistor
of
the
video
output
terminal
on
the
oscilloscope
screen,
adjust
R201
(EE
level
control)
to
obtain
the
value
indicated
in
Fig. 2-1 2.
1.0 Vp-p
200mV /div
e 20psec/div
Figure 2-12.
Ajustment of FM 3.8 MHz and 4.8 MHz
Frequenc
;
Oscilloscope
Recording
Self-recording
/
playback
Externalinput
|Standard
colour
(no
signal)
bar
(stair-case
waveform)
Measuring
instrument
Test point TP203 ,
ee ie 1¢201) |Video Signal
R222 (FM R220 (deviation
carrier control) | control)
3.8 MHz 1.0 + 0.05 Vp-p
Specification
Note. 1:
Carry out this adjustment only when 1C201 has —
been
replaced
or
when
the
carrier
setting
(3.8
MHz)
or
the
deviation
(4.8
MHz)
is
found
apparently
out
of
specification.
31
Vs OR £-18
VC-730ET
Make
this
adjusment
after
the
EE
level
has
been
completely adjusted.
Note. 2:
The video output terminal should be terminated
with a 75-ohm impedance.
1. First make sure that the EE level playback video
signal is at the speciffied level.
2. Place the unit in the record mode and get it
ready for external input.
Note:
Do not connect anything to the external input
terminal.
3. Hook up the frequency counter to TP203.
Adjust R222 (FM carrier control) so that the
counter reading be 3.8 MHz.
Note:
Make sure the white and dark clip controls are
not now applied to the waveform.
4. Feed the colour bar signal (stair-case waveform)
and make self-recording and playback.
5. Observe the video output terminal voltage
(across the terminal resistor) on the oscilloscope
screen. If the playback video signal level is below
1.0
Vp-p,
turn
R220
(deviation
control)
clockwise.
If above 1.0 Vp-p, turn the control counter-
clockwise. Now make self-recording and playback
again.
6. Repeat the above step 5 to finally get the
playback video signal level at 1.0+0.05 Vp-p, as
shown in Fig. 2-12.
Adjustment of white clip
Oscilloscope
Standard colour bar
(stair-case waveform)
TP201
R225 (white clip control)
+ 0
. Place the unit to the record mode.
. Feed the colour bar (stair-case waveform) signal.
3. Observing the output at TP201, adjust R225
(white clip control) so that the white peak
overshoot be 80 (tolerance +0-10)%.
Measuring
instrument
Input signal
Test point
Adjusting point
Specification
NM —
WHITE
CLIP
80%
100%
DARK ~-
CLIP
50%
200mvV /div
20pusec/div
Figure 2-13.