Toshiba DVR19DTKB2, Service Manual

Page: 108 / 124

2-3-4 N25E1FLMA
5. To shift the CTL waveform, press [PROGRAM ]
or [PROGRAM ] button. Then make sure that
the maximum output position of PB FM envelope
signal becomes within
±
2ms from preset position.
6. Set the Tracking Control Circuit to the preset posi-
tion by pressing [PROGRAM ] button and then
[
B
] (VCR) button on the unit.
1-C. Checking/Adjustment of Envelope
Waveform
Purpose:
To achieve a satisfactory picture, adjust the Guide
Rollers so that 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
BOARD AV. Use TP504 (RF-SW) as a trigger.
2. Playback the Gray Scale on the Alignment Tape
(FL6NS8). Set the Tracking Control Circuit to the
preset position by pressing [PROGRAM
] button
and then [
B
] (VCR) 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
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. M8, adjust the
height of Guide Roller [2] (Refer to Fig. M3) so that
the waveform looks like the one shown in Fig. M10.
4. If the envelope is as shown in Fig. M9, adjust the
height of Guide Roller [3] (Refer to Fig. M3) so that
the waveform looks like the one shown in Fig. M10.
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. M10.
Note: Upon completion of the adjustment of Guide
Rollers [2] and [3] (Refer to Fig. M3), check the X
Value by pushing the [PROGRAM
] or [PROGRAM
] buttons on the unit alternately, to check the sym-
metry of the envelope. Check the number of pushes to
ensure preset position. The number of pushes of the
[PROGRAM
] button on the unit to achieve 1/2 level
of envelope should match the number of pushes of the
[PROGRAM
] button on the unit from center. 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