Akai VS-2EGN

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3-1 GENERAL
VS-2 EGN includes PAL (SECAM) and NTSC servo cir-
cuits. The PAL (SECAM) servo circuit is mainly des-
cribed herein, and the description of the NTSC servo
circuit is limited to parts differring from the PAL
(SECAM) servo circuit.
In addition to the normal speed recording and playback
servo circuits, the VS-2 EGN servo circuit icnludes the
simplified still playback circuit for playback.
For PAL (SECAM), there are CUE (forward directin)
and REVIEW (reverse direction) servo circuits of about
7 times the normal speed.
Servo circuits are largely classified as follows:
1) Drum motor servo circuit
@ Drum motor phase control circuit
® Drum motor speed control circuit
© Drum motor drive circuit
2) Capstan motor servo circuit
@ Capstan motor phase control circuit
@® Capstan motor speed control circuit
© Capstan motor drive circuit &
Capstan motor starting current limiting circuit
3) Automatic editing control servo circuit
4) Quasi-vertical synchronization pulse generator cir-
cuit
5) PAL (SECAM)/NTSC switching circuit
6) Automatic discriminator circuit
The drum motor servo circuit and the capstan motor
servo circuit include the recording servo circuit, normal
playback servo circuit, about 7 times faster (about 5
times in PAL and NTSC modes) servo circuit, and ele-
ctronic editing servo circuit.
AKAI call the 7 times faster mode (NTSC 5 times)
QUICK FINDER, the forward direction is called CUE,
and the reverse direction is called REVIEW (or REV).
3-2 CAPSTAN SERVO CIRCUIT
The capstan servo circuit runs the magnetic tape at a
constant speed of 23.39 mm/sec (33.35 mm/sec in the
case of NTSC system), and it also controls the video
head so it runs accurately aligned with the recorded
video track during the playback,
In addition, when either a tape recorded by an other
maker’s VHS standard VTR or a pre-recorded tape is
reproduced, the video head path can be adjusted by the
TRACKING knbo on the front panel so that the video
head runs accurately over the video track.
Since the capstan motor is a DC motor, the servo re-
quires a phase control circuit and a speed control cir-
cuit.
For this reason, IC AN6341 which has a built-in phase
control circuit and a speed control circuit is used.
3-2-1 PHASE CONTROL
The Switching pulse (25 Hz for PAL/SECAM system, 30
Hz for NTSC system) form the drum motor servo circuit
(ICI pin 0) ) is supplied to IC11 (AN6341N) pin ®
as a reference signal A . Comparison signal is supplied to
IC11 pin ©. The comparison signal at used during the
time of recording differs from that at the time of during
playback. The comparison signal used during the CUE
mode differs from that during REVIEW.
Fig. 7-29 shows the reference signal and comprison sig-
nal of the capstan motor phase control circuit.
REFERENCE COMPARISON
SIGNAL SIGNAL
Mode
RECORDING | SWITCHING PULSE [CAPSTAN MOTOR FG _ 95 1,
PLAYBACK |SWITCHING PULSE CTL PULSE
CUE
or SWITCHING PULSE TL EVLSE
REVIEW
Fig. 7-29 Reference signal and comparison signal
of various modes
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Service
Manual
8-2
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