Adjustment Of Head Switching Point; Adjustment Of Fv (False Vertical Sync) Of Still Picture; Checking Of Off Track - Sharp VC-A598U Service Manual

VC-A598U/H995U/H996U
-H997U/H9977U/H998U
SERVO CIRCUIT ADJUSTMENT
5-1 ADJUSTMENT OF HEAD SWITCHING
POINT
Measuring Dual-trace oscilloscope
instrument
Mode Playback
Cassette Alignment tape (VROEFZCS)
Test point VIDEO OUT jack to CH2
TP202 (Sig.)~TP203 (GND) to CH1
Control R724 Head switching point adjust-
ment control
5.5 ± 0.5H (lines)
Specification
1. Remove the front panel and play the alignment tape.
2. 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.)
3. Playback the alignment tape, and then short circuit
between TP802 on the main PWB, and press both CH
button (+) and CH button (–) at same time.
4. Adjust R724 so that the leading edge of the head
switching pulse is 5.5H (lines) ahead of the vertical sync
as shown in Figure 5-2.
5. Cancel the short circuited.
CH-2
VIDEO OUT
CH-1
HEAD
SWITCHING
PULSE
CH-1: 1V/dev 50µsec/dev
CH-2: 2V/dev 50µsec/dev
5.5±0.5H (lines)
Figure 5-2.
5-2 ADJUSTMENT OF FV (False Vertical
Sync) OF STILL PICTURE
Measuring
instrument
Mode
Cassette
Control
Specification
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
instrument
Mode
Cassette
V-sync.
Control
Specification
1. Play a cassette which was recorded by the unit in EP
mode.
2. Short circuit between TP802 on the main PWB, and
press both CH button (+) and CH button (–) at same time.
3. Press the tracking buttons (+) and (–) 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. Cancel the short circuit.
Note:
Self-recorded tape is a cassette whose program was re-
corded by the unit being adjusted.
32
Color TV monitor
Playback still
Self-recorded tape (SP mode)
(See Note below 2)
Tracking control buttons(+) or (–)
No vertical jitter of picture
Color TV monitor
Playback
Self-recorded tape (EP mode)
(See Note below)
Tracking control buttons(+) or (–)
No Poor picture and Hi-Fi sound