Philips 20MC4304, Service Manual

Page: 284 / 316

2-3-4 MK14NMA_PC
5. To shift the CTL waveform, press [CHANNEL
K
]
or [CHANNEL
L
] buttons on the unit. Then make
sure that the maximum output position of PB FM
envelope signal become within
±
2ms from preset
position.
6. Set the Tracking Control Circuit to the preset
position by pressing [CHANNEL
K
] button and
then [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 variation of the Tracking
Control Circuit.
1. Connect the oscilloscope to TP (C-PB) on the
Main CBA. Use TP (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 [CHANNEL
K
]
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 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 [CHANNEL
K
] or [CHANNEL
L
]
buttons on the unit alternately, to check the symmetry
of the envelope. Check the number of pushes to
ensure preset position. The number of pushes
[CHANNEL
K
] button on the unit to achieve 1/2 level
of envelope should match the number of pushes
[CHANNEL
L
] 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