Dual C 844 - Page 7

The dynamic HIGH pulses
produced by Pin
14 to
Pin 20
(IC 409) are
converted to static HIGH signals
by the D-latch IC 408. The
informa-
tion pending
at the D input is written into the
clock input Pin 9 (IC
408) by a HIGH pulse
(approximately 10 ps) and is
available in static
form at
the Q output until new information is stored.
Capstan
motor,
reel
motor
With a HIGH signal from the processor (IC 409, Pin 16), which is stored
in the D-latch IC 408, Q 403 causes the transistor Q 402 to become
forward-biased and this applies the operating
voltage of — 16 V to the
Capstan
motor and reel motor, connector A (board C) Pin 10. The refe-
rence voltage for the
tape speed is set with VR 403 (9.5 cm/s) and
VR
402
(4.75 cm/s). The
phototransistor
in IC
411 is always
forward-
biased and only functions when the rewind
speed REW is regulated.
The flyvvheel of the Capstan drive is
implied via an intermediate linkage
for the FF or REW function. In
order to prevent excessive
stressing of
the tape at the end of
the reel, —
during the
function
REPEAT
= REW
and 9.5 cm/s — the
rewinding speed is slowed down towards the
end of
the reel via the optocoupler
IC 411. The signals of the tape
run sensor
IC 412 are evaluated by
the processor. If the pulse
frequency rises abo-
ve
75 Hz, LOW active
regulation pulses are routed from Pin
33 (IC
409)
through D 415 to the
inverter IC 406, Pin 2. The HIGH pulses from the
output Pin
15 control the photodiode in the optocoupler
IC 411. With
each
positive pulse, the integrated
phototransistor becomes reverse-bia-
sed and increases the reference voltage via
R 465. The Capstan motor is
slowed down
accordingly. In order to
ensure that the tape
reaches a
high rewinding speed
in FF mode, this regulation
function is cancelled
by a HIGH
signal via D 414 and the
phototransistor is
forward-biased.
Music finder
Pf
the buttons FF or REW
are operated during the play function, the
processor recognizes the music finder function and routes a LOW signal
= SCAN to Pin 31
(IC 409). This signal is routed to transistor Q 414 in
order to enable the finder amplifier. The magnets FF and MF (music
finder) are energized and, in this
way, the double-head only just tou-
dies the tape in order to
guarantee reliable recognition of the music
gap. Wear of the audio head is reduced to a minimum, thanks to this
bare touching.
Pf
a music gap is now recognized (SPACE = LOW active,
see also analog section), this LOW signal is routed to the processor in-
put Pin
38 which initiates the play
function.
Auto-space
When the AUTO SPACE button is operated during RECORD mode,
the
recording amplifier is muted — HIGH signal
from Pin 32 (IC
409)
to
Q
419 — and the
tape runs approximately 4 s more until the
processor
stops the tape and triggers off RECORD STANDBY. With the com-
mand PAUSE (HIGH active Pin 20 of IC 409), Q 419 becomes
reverse-
biased = clear muting playback by a LOW signal via IC
408 and inverter
IC
406.
Record st andby
Pf the
button
RECORD
is
operated and
the
contact
RECORD
SAFETY S 13 is closed (LOW
at Pin 36,
IC
409),
the deck
changes over
to the
function
RECORD
STANDBY which
is indicated
by flashing
of
the
green LED
PLAY. The
magnet PLAY
is
energized, muting of
the
playback
branch is
cancelled (clear
muting
playback),
the Capstan
mo-
tor is
switched
on, the
recording
amplifier is
enabled
(clear muting
RA,
419 reverse-biased),
the
LED PLAY flashes
and
the LED
RECORD
lights up.
Pf the button
PLAY is
now
operated, the
deck changes
over
to the
record function.
LED
display
The
functions
STOP, PLAY,
RECORD,
REPEAT
and DOUBLE
SPEED
(9.5 cm/s)
are each
indicated
by one
LED. With
the
exception of
DOUBLE SPEED, the
LED's are driven
on their
cathode sides with
the
LOW active decade
pulses
(inverter
IC 406). The positive
operating
vol-
tage is connected
es pulses
with
the
transistors
0416 and
0417.
Pf, for
example, the LED
RECORD is
activated, the
processor
produces the
activation pulses for
0
416
in phase
with the
pulses of
decade 2.
Pf,
on
the other
hand, the LED
REPEAT is to light
up, the
activation pulses
for
0416
are synchronous
with the
pulses of
decade 4.
Counter
The
4-digit
display is driven in multiplex
mode via inverter IC 406 (de-
cade pulses LOW
aktive) and
inverter IC
407 (segment pulses LOW ac-
tive).
Display of the dots for MEMORY and SET is controlled by 0416
and Q 417.
T = 12 ms
t = 3 ms
Pulse
Diagramm
IC
409
Pin
IC
409
--..-
Dek. 1
6
Dek. 2
7
Dek. 3
Dek. 4
9
Record Switch
3
Memory Switch 3
Pause Switch
4
Q416 LED Rec. 28
0416 LED Rep. 28
Q 416
LED
Rec,
28
+ Rep.
T
131
I L
3
zi rzi 4
21 12
2 2
4l 14
21 141 2 4
i
I I I I
3 6 9
12 15 1821
24
t(ms)
Remote
control
The
IR signals
converted to
electrical pulses
by the
infrared receiver are
routed
via C
413 and
inverter IC 405 Pins
11/10 and Pins 9/8 to the
in-
put Pin 35
of the
processor IC
409.
Cause
of the
signals: A
coded
command
consists of 16
bits. As each
transmitted
command is
repeated for
increased
reliability,
commands
consist of 2 x
16 bits = 96
ms
duration. One bit
corresponds to
a length
of 3 ms
and isclocked
with a
frequency of
approximately
28.5 kHz.
Point A:
Point B:
Point
C:
Point D:
Point E:
The
clocked bits
are applied
es voltage
fading.
The
signals are
differentiated and
limited to 5
V with C
413
and R
456 (diodes D
411 and
D412).
The
pulses are
negated by the
inverter IC
405.
Positive needle
pulses are now
applied.
The pulses are
integrated
by R 454
and C
412.
Inverter IC
405 negates
and a
positive pulse
= 1 bit
with a
duration of
approximately 3 ms
is applied
at the
input of the
processor.
This
method
ensures good
suppression
of noise
pulses. Points
A to E are
identical with
the
designations in
the
circuit
diagram.
ca.
18V
A
OV
5V
B o
V
5V
C OV
5V
D OV
5V
E ov
1.
Bit
Störung
\
2. Bit
\ 11 /
V
I I
fl 11
FT. Bit
1
/7.
2.Bit
nds
7