Sharp vc-ga56z, Service Manual

Page: 30 / 74

30
VC-GA56Z
VC-GH96Z
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 R701 Head switching point adjust-
ment control
Specification 6.0 ± 0.5H (lines)
6.0
±
0.5H (lines) CH-1
HEAD
SWITCHING
PULSE
CH-2
VIDEO OUT
CH-1: 1V/dev 50
µ
sec/dev
CH-2: 1V/dev 50
µ
sec/dev
V-sync.
Figure 5-2.
Measuring Color TV monitor
instrument
Mode Playback still
Cassette Self-recorded tape (SP mode)
(See Note below 2)
Control Tracking control b) or (–)
Specification No vertical jitter of picture
Measuring Color TV monitor
instrument
Mode Playback
Cassette Self-recorded tape (EP mode)
(See Note below)
Control Tracking control b) 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
recorded by the unit being adjusted.
5-2 ADJUSTMENT OF FV (False Vertical
Sync) OF STILL 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 (–)
TRACKING 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.
Notes:
1 The FV goes back to it’s initial state when the unit is put
into the system controller reset mode due to power
failure and 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
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 TP801 and TP802 on the operation PWB.
4. Adjust R701 so that the leading edge of the head
switching pulse is 6.0H (lines) ahead of the vertical
sync as shown in Figure 5-2.
5. Cancel the short circuited.