Dual C 844 Serviceanleitung Seite 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
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
7