Sharp 27DV-S100 Service Manual page 37

ADJUSTMENT OF TAPE DRIVE TRAIN
1. Tape run rough adjustment
1 Remove the cassette housing control assembly.
2 After shortcircuiting R7057 and JUMPER:420
provided on the main PWB, plug in the power cord.
, then turn off the power. Set the tape for each check
and / or adjustment shown below and turn on the
power.
3 Check and adjust the position of the tension pole.
(See page 33.)
4 Check and adjust the video search rewind back
tension. (See page 32.)
5 Connect the oscilloscope to the test point for PB
CHROMA envelope output (TP3301). Set the syn-
chronism of the oscilloscope to EXT. The PB
CHROMA signal is to be triggered by the head
switching pulse (TP3302).
6 Set the alignment tape (VROATSV) to play. (Put a
500g weight on the cassette tape to prevent lift of
cassette tape.)
Guide roller
Figure 1-31.
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 1-35.)
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.
• Problems caused by maladjustments
1. Totally maladjusted
• Images onscreen may get distorted or affected by
noises, or may fail to appear.
Notes:
1. Previously set the tracking control in the center posi-
Cassette Tape
500g
Weight of 500g
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.
Figure 1-32.
2. Adjustment of A/C head height and azimuth
1 Perform the initial setting of A/C head position by
the method stated in "page 35 Replacement 3".
2 Connect the oscilloscope to the audio output
termina0l (TP6601).
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.
For X value adjustment
Adjust the X value, turning the
gear-type screwdriver.
Figure 1-33.
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 page 35 "Replacement 3".
After shortcircuiting R7057 and JUMPER:420, plug
in the powercord, then turn off the power. And set
the alignment tape (VROATSV) into the unit, turn
on the power, then playback it. 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 1-33, 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 page 35.)
37
27DV-S100
27DV-CS10