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3-6-2..(nitial reset circuit
See Fig. 3-12 and 3-13.
operate as DC voltages are rising.
1) When a cassette tape is not loeded
When the deck is not loaded with a cassette
tape, Cassette In Switch $994 is closed to the
NO side. This is the state which the deck en-
ters when the STOP button is kept depressed.
Therefore, the deck will enter Stop mode as
s00n as you turn on power.
2) When a cassette tape is loaded
When the deck is loaded with a- cassette tape,
Cassette In Switch $994 is closed to the NC
side and separated frorn the stop circuit. lf
you turn on power 'at this time, +10 V rises
gradually. Since it-charges-capacitor C754 -first
via path (1), voltage rise at pins 8 and 9 of
U7S1
delays for approx. 2.6 seconds almost
equalling
the -time--constant
of -R7&3-~and
C751. At first, therefore, the level at (a) is L.
tween
(a) and (c) shape the waveform
for
sharp rise and decay to secure operation of
the circuit. The level at (c) is L since the input
voltage
is inverted
twice.
The
succeeding
NAND
gate inverts the L-level again and the
level at (d) is H. Thus H-level is applied to the
controller's
RESET. terminal
when the DC
voltage has not. risen sufficiently,
and the
controller is reset. This-prevents the controller
from operating erroneously.
CONTROLLER
When
the DC voltage has risen sufficiently
and capacitor C751
is completely charged,
level turns to H at (aj, L at (b}, H at (c), and
tL at (dj). As a result, the reset signal of the
controller is released.
Next, let us see how the circuit operates when
'you turn off power.
Capacitor C752 is charged by the DC voltage
via path (2). If you turn off the power, the
voltage at the base of transistor Q751 falls be-
low the voltage across capacitor C752 and,
therefore, base current flows from C752. via
path (3). This turns on Q751 and permits cur-
rent to flow via path (4). This current turns
pins 5 and 6 of U751 to H-level and U751
outputs
L-level at pin 4:-Therefore, charges
storaged in C751
flows out via path (5) and
level turns to L at (a}.-As-4a}-is at L-level, (d)
is at H and the controller gets reset as explain-
ed first. A small time constant is selected for
path. (5)..and..the..controiler .wsill .be reset im-
mediately when. power gets turned off. Thus
the. system is protected from erroneous opera-
tion at the time of power-off.
3-7. COMMAND
INPUT CIRCUIT
The--controller- LS!
-44PD554-80} controls the
system extensively according to commands. The
'command input circuit permits proper-command
input to the controller.
As briefed in Section
3-1, two multiplexers,
operating key switches,
and Auto-Present
rotary
switch,
etc, are con-
nected to the controller (see next page).
Fig. 3-12.
Initial reset circuit
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