Sharp 14VT10X1, Service Manual

Page: 36 / 138

Adiustment of FM 3.8 MHz and 4.8
M
HZ
Measuring
Frequency
instrument
counter
Osci I
Mode
Recording Self-recording/
.
Adjusting R227 (FM R228 (Deviation
point carrier control) control)
Specification 3.8 2.0
M H z
Note
Carry out this adjustment only when
has
or when the carrier setting (3.8 MHz)
or the deviation (4.8 MHz) is found apparently out
of specification.
Make this adjustment after the EE level has been
completely adjusted.
1. First make sure that the EE video signal level is at
the specified 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 TP205 and
TP202. Adjust R227 (FM carrier control) so that
the counter reading be 3.8 MHz.
Note
Make sure the white clip control is not now
applied to the waveform.
4. Feed the bar signal and make
recording and playback.
5. Observe the voltage of pin of (video
output) on the oscilloscope screen. If the
playback video signal level is above 2.0 Vp-p,
turn R228 (deviation control) clockwise.
If below 2.0 Vp-p, turn the control counter-
clockwise. N o w m a k e s e l f - r e c o r d i n g a n d
playback again.
6. Repeat the above step 5 to finally get the
playback video signal level at 2.0 0.08 Vp-p, as
shown in Figure 2-7.
- -
Figure 2-7.
Adjustment of recording current
Measuring
instrument
I
Osci I
Mode
Input signal
Test point
Recording
Standard bar
(stair-case waveform)
(GND at TP302)
External trigger
(video output terminal)
Adjusting
R255
point
(recording FM (recording
control)
control)
Sync tip level:
Red level:
tion 1 4 0 2 4
Note:
and TP302 are located on the head amp
Place the unit to the record mode.
2. Feed the bar signal to the video input
terminal.
3. Observing the waveform on the oscilloscope
screen (external trigger at pin of
output)), take the following steps.
a) Connect the oscilloscope’s ground and signal
leads to TP302 and respectively.
R255 (recording FM control) to min-
imum.
c) Adjust (recording control) so
that the red level be 24 as shown in
Figure 2-9.
4. Adjust R255 (recording FM control) so that the
sync tip be as shown in Figure
38