Dual C 839 RC Service Manual page 4

Co nt ro I
All functions of the unit and drive mechanism are controlled by
a processor. By connecting a separate infrared receiver RE 120
and using the infrared transmitter RC 152, all functions of the
unit may be remotely controlled. If connected to amplifier CV
1500 RC, RE 120 may bedispensed with. The infrared commands,
converted into electrical pulses, are switched to a bus line via an
infrared evaluation circuit. The bus line is then processed by the
processor. The processor takes over the following tasks:
1. Scanning the pulse train
2. Fi ltering out interference
3. Identifying device-specific commands
4. Executing the command which has been identified.
The processor is accomodated in a separate assembly. The L-plug
forms the Interface between the processor and the subsequent
device electronic system. The levels may be checked at plug L by
means of the status matrix.
Inputs
All locally controlled functions and keys issue their information
as active low. The contacts record lock <and record lock
(music cassette inserted = contacts open) issuetheir information
as a high signal to two series-connected 8-bit shift registers IC 4503
and IC 4504. The data is then supplied serially to the processor
via plug L 3. The shift clock pulse is issued via L 2 and switchover
from parallel to serial input is issued by the processor at L 8. The
signal "rewind motor stopped or operating" is input as a serial
input to the shift register IC 4505, pin 11. The pulsating voltage
at the emitter of T 4518 is converted by the circuitry, consisting
of transistor T 4524 and T 4525, into a logic, static signal.
Low = rewind motor operating and high = rewind motor stop.
The contact, cassette senso r closed = cassette inserted, isarranged
in series with the DLLS contacts. Contact closed = DLLS not
actuated = DLLS off. This signal is scanned by the processor via
plug L 7 directly (low). The infrared signals of the bus line are
applied to plug L 9.
Outputs
The data for the LED displays are issued serially by the processor
via plug L 2 to two 4-bit shift registers (IC 4505 pin 7). The rele-
vant shift pulse is applied to pins 1 and 9 from L 1. The signals
which are now applied in parallel are applied to an 8-segment
constant current driver IC 4506 which drives the individual
LED's. The LED register acknowledges a music cassette in the
form of a low signal at transistor T 4526 via pin 5. This transistor
T 4526 via pin 5. This transistor becomes biased in the reverse
direction, blocking the RF generator with its high level at the
collector via plug T 2.
The capstan motor is a dc rotor which is maintained at constant
speed by means of a speed regulator IC 4501. A generator is
located in one of the two capstan flywheels. The pulses which it
generates, proportionate to the speed, are amplified by transistor
T 4500 and supplied to IC 4501 at pin 3. Via the analog circuit
IC 4500 8/9, R 4506 and trimmer R 4505 form a voltage divi-
der between pins 11 and 5 of IC 4501 together with trimmer
R 4503 and R 4504. The set speed during playback mode is set
by means of R 4505 and, during record mode, by means of
R 4503. lt is imperative that its sequence be observed. A high
signal at plug L 13 (record) in conjunction with the service plug
being in position N, means that the analog switch 4/3 operates,
applying 0 V to switch 10/11. This switch opens and the pitch
control at plug point K 1 and K 2 is isolated from the voltage
divider. This guarantees that, during record, absolute tape speed
is maintained even if the pitch control is adjusted. The high
record signal also reaches plug 1 in order to start the RF genera-
tor and plug R 8 in order to maintain the magnet record in hold
condition.
The dc voltage is alternately connected to the motor by means
of the H circuit, formed by transistors T 4504, T 4506, T 4505
and T 4507. A high signal at plug L 12 (capstan motor clockwise)
causes transistor T 4503 to become biased in the forward direc-
tion, applying a high signal to the base of T 4507, applying 0 V
to the motor and biasing the PNP transistor T 4504 in the for-
ward direction. This applies the positive voltage to the motor.
Transistor T 4502 readjusts the operating current on the basis of
the switching pulses issued by the speed regulator IC 4501.
The rewind motor, comprising a dc rotor, is operated in two
directions and at two speeds. Once again, an H circuit consisting
of switching transistors T 4515, T 4521,T 4517 and T 4522 are
central to reversing the direction of rotation. A constant current
source supplies the operating current by means of transistor
T 4518. A high signal at the base of T 4512 causes it to be biased
in the forward direction. The high signal reaches the base of
T 4520 which now couples the constant current source to the H
circuit. When the direction is fed in, the motor operates in fast
mode. On the other hand, If transistor T 4511 becomes conduc-
tive owing to a high signal, (command: rewind motor slowly),
transistor T 4514 becomes biased in the forward direction, de-
creasing the operating current supplied by the constant current
source via R 4534. The motor now operates in slow mode and
tape tension is set by means of trimmer R 4524. The direction of
rotation is preset by connecting transistors T 4513 (wind motor
left) and T 4519 (wind motor right). Transistors T 4523 and
T 4516 serve to delay connection.
When transistor T 4511 (wind motor slowly) is activated, T 4510
becomes biased in the forward direction and the solenoid "play"
(in the drive system) located in the collector circuit thereby res-
ponds. A high signal at the base of T 4509 causes the solenoid
"pause" (in the drive system) to respond via T 4508.
The solenoid drivers are also driven by high signals via plug R 7
for solenoid track >and R 6 for solenoid treck <Solenoid re-
cord requires two operator commands. A high signal at plug R 5
applies —12 V to the solenoids. When there is a high signal at
plug R 8 (solenoid record hold), the +12 V are applied causing
the solenoid to respond rapidly. When the signal at R 5 (solenoid
operative) is removed, the record solenoid remains at hold status
via diode D 4415 with 0 V applied.
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