Hitachi DV-PF35U, Руководство по обслуживанию

Страница: 41 / 102

4-7
5. To shift the CTL waveform, press “CH
K
” or “CH
L
”
button on the remote control unit. Then make sure
that the maximum output position of PB FM enve-
lope signal become within
±
2ms from preset posi-
tion.
6. Set the Tracking Control Circuit to the preset posi-
tion by pressing “CH
K
” button and then “VCR-
PLAY” button on the unit.
1-C. Checking/Adjustment of Envelope
Waveform
Purpose:
To achieve a satisfactory picture, adjust the PB FM
envelope becomes as flat as possible.
Symptom of Misalignment:
If the envelope output is poor, noise will appear in the
picture. The tracking will then lose precision and the
playback picture will be distorted by any slight varia-
tion of the Tracking Control Circuit.
1. Connect the oscilloscope to TP301 (C-PB) on the
Main CBA. Use TP302 (RF-SW) as a trigger.
2. Playback the Gray Scale on the Alignment Tape
(MH-1). Set the Tracking Control Circuit to the pre-
set position by pressing “CH
K
” button and then
“VCR-PLAY” button on the unit. Adjust the height of
Guide Rollers [2] and [3] (Fig. M3, page 4-6) watch-
ing the oscilloscope display so that the envelope
becomes as flat as possible. To do this adjustment,
turn the top of the Guide Roller with the Guide
Roller Adj. Screwdriver.
3. If the envelope is as shown in Fig. M7, adjust the
height of Guide Roller [2] (Refer to Fig. M3) so that
the waveform looks like the one shown in Fig. M9.
4. If the envelope is as shown in Fig. M8, adjust the
height of Guide Roller [3] (Refer to Fig. M3) so that
the waveform looks like the one shown in Fig. M9.
5. When Guide Rollers [2] and [3] (Refer to Fig. M3)
are aligned properly, there is no envelope drop
either at the beginning or end of track as shown in
Fig. M9.
Note: Upon completion of the adjustment of Guide
Rollers [2] and [3] (Refer to Fig. M3), check the X
Value by pushing the “CH
K
” or “CH
L
” buttons on the
unit alternately, to check the symmetry of the enve-
lope. Check the number of pushes to ensure preset
position. The number of pushes “CH
K
” button on the
unit to achieve 1/2 level of envelope should match the
number of pushes “CH
L
” button on the unit from cen-
ter. If required, redo the “X Value Alignment.”
No Good
Good
FM envelope output signal is low.
2ms
FM envelope signal
CTL signal
Center Position
FM envelope output signal
is adjusted at maximum.
Fig. M7
Dropping envelope level at the beginning of track.
Fig. M8
Dropping envelope level at the end of track.
Fig. M9
Envelope is adjusted properly. (No envelope drop)
Fig. M10