Philips DVP620VR/78 Service Manual page 82

5. To shift the CTL waveform, press CH UP or CH
DOWN button on the remote control unit. Then
make sure that the maximum output position of PB
FM envelope signal become within
set position.
Good
FM envelope signal
FM envelope output signal
is adjusted at maximum.
No Good
FM envelope output signal is low.
6. Set the Tracking Control Circuit to the preset posi-
tion by pressing CH UP button on the remote con-
trol unit. and then "PLAY" button.
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
(VFMS0001H6). Set the Tracking Control Circuit to
the preset position by pressing CH UP button and
then "PLAY" button on the unit. Adjust the height of
Guide Rollers [2] and [3] (Fig. M3, Page 2-3-3)
watching the oscilloscope display so that the enve-
lope becomes as flat as possible. To do this adjust-
ment, 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.
±
2ms from pre-
2ms
Center Position
CTL signal
Fig. M7
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.
Dropping envelope level at the beginning of track.
Dropping envelope level at the end of track.
Envelope is adjusted properly. (No envelope drop)
Note: Upon completion of the adjustment of Guide
Rollers [2] and [3] (Refer to Fig. M3), check the X
Value by pushing the CH UP or DOWN buttons alter-
nately, to check the symmetry of the envelope. Check
the number of pushes to ensure preset position. The
number of pushes CH UP button to achieve 1/2 level of
envelope should match the number of pushes CH
DOWN button from center. If required, redo the "X
Value Alignment."
2-3-4
Fig. M8
Fig. M9
Fig. M10
H9622MA