Table of Contents
Advertisement
-From the truth table of U914, we also find the
states of the output terminals as given in Table
3-7. As the reel motor is connected across Vout1
and Vout2, drive current flows from RED to
BLK (see Fig. 3-19) and drives the motor to run
forward. during PLAY and REW modes. During
F.FWD mode, drive current flows from BLK to
RED
and the motor
reverses the direction of
rotation. Except in PLAY mode, a voltage (13 V)
which is close to the supply voltage is applied to
terminal VR of U914 for the reason described
below so that a voitage as high as approximately
11.5 V. developing
across
Vout!
and
Vout2
drives the motor at high speed.
In PLAY mode, the voltage is reduced. to about
4.5 V. The reason that the drive voltage is varied
is described below.
The H-level output at pin 11 of controller IC
U913 during PLAY mode is appiied-to thease
of transistor Q912
via resistor U9O1E
with a
delay (of 1.2 sec) which capacitor C903 deter-
mines together with -U901E..-Q9172-remains cut
off for the delay time and, during this time, the
supply..voltage.is-applied. to..the.terminal.V.RB_of
{iC U914 that controls reel motor drive voitage
via resistors R921 and R920. Therefore, the volt-
age across Vout1
and Vout2 is high to provide
the reel motor with enough starting torque.
After -the-delay~time (1.2 sec) which G903 and
U901E determine has elapsed, the base of Q912
rises to H-level and base current-flows through
it. This
turns on 0912, and terminal VR
of
-U914 gets locked to a level (approx. 5.1 V)
which
is close to the zener voltage of zener
diode D911 connected to 0912's collector. Now
some gates of the IC reduce the voltage across -
Voutl
and Vout2 approximately
to 4.4 V to
provide the reel motor with a drive torque which
is just enough to keep it running in PLAY (REC/.
PLAY) mode.
3-10. CAPSTAN
MOTOR
DRIVE
CIRCUIT
See Fig. 3-21.
The capstan motor operates during PLAY(REC/
PLAY)
and PAUSE
(REC/PAUSE)
modes.
Its
rotation is transmitted by belt to the flywheel
and further to the flywheel shaft which is just
the capstan shaft.
During PLAY,
REC/PLAY,
and
REC/PAUSE
modes, controller 4G-44943-cutputs H-level-at-pin
12 (output terminal of head base solenoid con-
trol signal). The H-level developed at pin 13 is
~applied to the.base.of .transistor.O909,
thereby
turning it on. As Q909 is on, Q910 also turns
_on, thereby closing'
the ground line of the servo
amplifier via 0991. The hot line of the servo am-
plifier is directly connected.to.the supply-power, .. ...
'Therefore, as soon as the ground line gets closed,
the
servo
amplifier
operates
and
the capstan
--moterstarts. Capstan-motor speed maybe select-
ed out of STD
(tape speed: 4.76 cm/sec) and
HIGH (9.5 cm/sec} with SPEED 'switch' $11-2.
GAPSTAN
MOTOR
STO
SPEED
Su-2
Fig. 3-21.
Capstan motor drive circuit
&
Advertisement
Table of Contents
