Nakamichi 481, Service Manual

Page: 11 / 66

11
2.3. Mechanism Control Circuits
2.3.1. Outline
(1) Control Button Operation
Record, Rewind, Stop, Play, and Fast-Forward Buttons
consist of a 5—way switch and are interlocked each other.
When one button is pressed, it is mechanically locked in
the ON state and other buttons are mechanically released.
Stop Button is of momentary type and acts to release
other buttons mechanically. But it is not used to control
circuits electrically. Pause Button is independent from
others and is of push-on and push-off type. Note that if
two or more buttons are pressed simultaneously, these
buttons are locked in the ON state. Under the normal con
trol button operation, only Record and Play Buttons are
pressed simultaneously to set the N-481 in RECORD
mode. In this case, both Record and Play Buttons are
locked in the ON state and RECORD mode is set. The
N-481 is designed so as not to occur erroneous operation
even if two or more buttons are pressed simultaneously.
Further, to prevent from abnormal tape tension, loosening
of tape, etc., the N-481 changes its mode by passing
through momentary STOP mode automatically, for ex
ample, when PLAYBACK mode is commanded while FF
mode, or REW mode is commanded while FF mode.
(2) Auto Shut-off Function
Refer to Fig. 2.3.1 basic circuit diagram.
During FF, REW, or PLAY (PLAYBACK or RECORD)
mode, auto shut-off will be activated when the tape comes
to end, and FF, REW, or PLAY mode is changed to STOP
mode.
Following explanation is made in regard to REW mode:
In the initial condition, Q428 is turned ON and +24 VS is
applied to the emitter of
Q 402. When Rewind Button is
pressed, it is locked in the ON state, as a result, Q 402 is
turned ON, the REW signal becomes H, and the N-481 is
set in REW mode.
When tape-end comes, auto shut-off is activated and
Q 428 is turned OFF, as a result, +24 VS is shut-off, Q402
is cut off, and the REW signal becomes L. In this way,
REW mode is changed to STOP mode. (Note that Rewind
Button is still locked in the ON state.) When Play Button is
pressed in this state, REW Button is released and
Q 428 is
turned ON, as a result, +24 VS is applied again, Q 418 is
turned ON, the PLAY signal becomes H, and the N-481 is
set in PLAY mode.
(3) Unattended Recording or Playback
Unattended recording or playback is carried out by the
use of the lock mechanism of control button, therefore, no
special circuit is required for this purpose.
If Record and Play Buttons are pressed, unattended re
cording can be carried out when the power is connected
to the N-481. If only Play Button is pressed, playback will
be carried out when the power is connected to the N-481.