Sharp vc-ga56z, Service Manual

Page: 21 / 74

21
VC-GA56Z
VC-GH96Z
4-18. ADJUSTMENT OF TAPE DRIVE TRAIN
1. Tape run rough adjustment
1
Remove the cassette housing control assembly.
2
After shortcircuiting TP803 and TP802 provided at
operation PWB, plug in the power cord.
3
Check and adjust the position of the tension pole.
(See 4-12.)
4
Check and adjust the video search rewind back
tension. (See 4-10.)
5
Connect the oscilloscope to the test point for PB
CHROMA envelope output (TP201). Set the syn-
chronism of the oscilloscope to EXT. The PB
CHROMA signal is to be triggered by the head
switching pulse (TP202).
6
Set the alignment tape (VROATSV) to play. (Put a
500g weight on the cassette tape to prevent lift of
cassette tape.)
7
Press the tracking button (+), (–) and change the
envelope waveform from max to min and from min
to max. At this time make sure that the envelope
waveform changes nearly parallel.
8
Unless the envelope waveform changes nearly
parallel, adjust the height of supply side and take-
up side guide roller so that the envelope waveform
changes nearly parallel. (For envelop adjustment
procedure refer to Figure 4-35.)
9
Turn the tilt screw to remove the tape crease at the
fixing guide flange.
Playback the tape and check for tape crease at the
fixing guide flange.
(1) If there is no tape crease
Turn the tilt screw clockwise so that tape crease
appears once at the flange, and then return the
tilt screw so that the crease disappears.
(2) If there is tape crease
Turn counterclockwise the tilt screw so that the
tape crease disappears.
(Reference) If the tilt screw is turned clockwise
crease appears at the lower flange.
Notes:
1. Previously set the tracking control in the center posi-
tion, and adjust the envelop waveform to maximum
with X value adjustment nut. Thereby the tape run
rough adjustment is facilitated.
2. Especially the outlet side envelope waveform must
have higher flatness.
2. Adjustment of A/C head height and azimuth
1
Perform the initial setting of A/C head position by
the method stated in "4-15 Replacement 3".
2
Connect the oscilloscope to the audio output termi-
nal.
3
Using the alignment tape in which 1 kHz linear
audio signal has been recorded, adjust the height
screw so as to get max audio output.
4
Using the alignment tape in which 7 kHz linear
audio signal has been recorded, adjust the azimuth
screw so as to get max audio output.
5
The adjustment of
3
and
4
twice or three times
repeat, and finally adjust
4
.
3. Tape run adjustment
1
Connect the oscilloscope to PB CHROMA enve-
lope output test point, set oscilloscope sync to EXT,
trigger-input the PB CHROMA signal (head switch-
ing pulse).
2
Rough adjustment of X value
Tentatively fix A/C head arm screws
1
and
2
by the
method described in 4-15 "Replacement 3".
Playback the alignment tape (VROATSV) and
shortcircuit TP801 and TP802. As a result the auto-
tracking is automatically cancelled, so that the X
value adjustment mode is set.
Move the A/C head with the X value adjustment
gear driver (JiGDRiVER-6) by the method shown in
Figure 4-33, and adjust the A/C head so as to get
the maximum envelope waveform. (Note: When
the A/C head is adjusted, adjust so that the maxi-
mum envelop waveform is obtained nearest the
position of initial setting made in 4-15.)
Guide roller
500g
Weight of 500g
Cassette Tape
Figure 4-31.
Figure 4-32.
For X value adjustment
Adjust the X value, turning the
gear-type screwdriver.
Figure 4-33.