Sharp XA-920 Service Manual page 31

SERVO CIRCUIT ADJUSTMENT
5-1. ADJUSTMENT OF HEAD SWITCHING
POINT
Measuring Dual-trace oscilloscope
instrument
Mode Playback
Cassette Alignment tape (VROEFZHS)
Test point VIDEO OUT jack to CH2
TP202 (Sig.)~TP203 (GND) to CH1
Control Call up the test mode (short circuit
between TP801 and TP802 on the
operation PWB). Use the tracking/channel
select (') and (") buttons of the set.
6.0 ± 0.5H (lines)
Specification
1. Connect a dual-trace oscilloscope to the VIDEO OUT
jack and TP202 (Sig.) and TP203 (GND).
(Trigger the oscilloscope with the head switching pulse
on TP202.)
2. Playback the alignment tape, and then short circuit
between TP801 and TP802 on the operation PWB to call
the test mode.
3. Press the PLAY button, and the play icon starts flashing
in the display and the automatic adjustment function
gets started.
4. Wait until the play icon in the display stays on to indicate
that the adjustment is complete.
5. Watch the oscilloscope screen and make sure that the
leading edge of the head switching pulse is 6.0H
(lines) ahead of the vertical sync as shown in Figure
5-2.
6. If the setting is out of this range, readjust the data
using the channel select (') and (") buttons of the
set or the remote controller.
7. Finally press the STOP button to quit the test mode.
CH-2
VIDEO OUT
CH-1
HEAD
SWITCHING
PULSE
Figure 5-2.
CH-1: 1V/dev 50µsec/dev
CH-2: 1V/dev 50µsec/dev
6.0 ± 0.5H (lines)
V-sync.
5-2. ADJUSTMENT OF FV (False Vertical
Sync) OF STILL PICTURE
Measuring Color TV monitor
instrument
Mode Playback still
Cassette Self-recorded tape (SP mode)
(See Note below 2)
Control Tracking control buttons(+) or (–)
Specification No vertical jitter of picture
1. Play a cassette which was recorded by the unit in SP
mode.
2. Press the PAUSE/STILL button to freeze the picture.
3. Look at the monitor screen and adjust (+) or (–) TRACK-
ING buttons so that the vertical jitter of the picture is
minimized.
4. Play and freeze the self-recorded tape in EP mode and
make sure vertical jitter of the picture is not noticeable.
Note:
1 The FV goes back to the it's initial state when the unit is
put into the system controller reset mode due to power
failure, etc.
In this case, preset the FV once again.
2 Self-recorded tape is a cassette whose program was
recorded by the unit being adjusted.
5-3. CHECKING OF OFF TRACK
Measuring Color TV monitor
instrument
Mode Playback
Cassette Self-recorded tape (EP mode)
(See Note below)
Control Tracking control buttons(+) or (–)
Specification No Poor picture and Hi-Fi sound
1. Play a cassette which was recorded by the unit in EP
mode.
2. Short circuit between TP801 and TP802 on the opera-
tion PWB to center tracking.
3. Press the tracking buttons (+) or (–) 20 times each to
bring the tracking off center. Make sure that:
1) There is nothing unusual on the playback screen.
2) There is nothing unusual in the Hi-Fi sound (for the Hi-
Fi models only).
4. Press the STOP button to quit test mode.
Note:
Self-recorded tape is a cassette whose program was re-
corded by the unit being adjusted.
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XA-905
XA-920