Sharp VC-780E Service Manual page 32

Ve FOUL
VC-790ET
Adjustment of dark clip
[Mode | Recording
ee
| Standard colour bar
(stair-case waveform)
Adjusting point R224 (dark clip control)
Specification 50 + 10%
1. Place the unit to the recording mode.
2. Feed the colour bar (stair-case waveform) signal.
3. Observing the output at TP201, adjust R224 (dark
clip control) so that the dark peak overshoot be
40 + 10%. (See Fig. 2-13.)
Adjustment of recording current
Measuring
inctriment Oscilloscope
Input signal Standard colour bar
(stair-case waveform)
Test point TP301 (GND at TP302)
External trigger
(video output terminal)
R3304 R518 (recording
{recording FM | chroma control)
control)
Specifica- | Sync tip level Red level
tion |84 + 4dmVp-p [18 + 1mVp-p
Note:
TP301 and TP302 are located on the head amp
PWB.
1. Place the unit to the record mode.
2. Feed the colour bar (stair-case waveform) signal.
3. Observing. the waveform on the oscilloscope
screen (external trigger at video output
terminal), take the following steps.
a) Connect the oscilloscape's GND and SIG leads
to TP302 and TP301, respectively.
b) Turn R3304 (recording FM control) to
minimum,
c) Adjust R518 (recording chroma control) to
that the red level be 20 + 1mVp-p as
shown in Fig. 2-14.
4, Adjust R3304 (recording FM control) so that the
sync tip be 100 + 10mVp-p as shown in Fig. 2-
15.
20 £ 1mVp-p
Figure 2-14.
Figure 2-15.
@ ADJUSTMENT OF Y/C PLAYBACK CIRCUIT
Adjustment of playback video signal level
Measuring .
[wode «Payback
Tape used Alignment tape
(stair-case waveform)
Test point Video output terminal
Adjusting point R414
(playback level control}
1.0 0.0508
Note:
The video output terminal should terminated with
a 75-ohm impedance.
1. Insert the alignment tape (stair-case waveform)
and place the unit to the playback mode.
2. Hook up the oscilloscope to the video output
terminal. Adjust R414 (playback level control) so
that the on-screen waveform be 1.0 +0.05Vp-p.
1.0 Vp-p
Figure 2-16.