Dual C 824 Serviceanleitung Seite 5

Dev ice control
Processor
All device and drive control functions are controlled by a 4 bit micro-
computer with an integrated 2 k-byte program memory. The clock fre-
quency from CF 401 supplied at pins 24 and 25 of the processor IC 403
is approximately 455 kHz.
Reset
When the C 824 is switched on, the power supply voltages reach their
nominal value. This LOW-HIGH edge at the reset input, pin 23 of IC 403
sets the program counter of the processor to its start address and enables
the processor for its mquences of function.
Inputs
The drive control buttons are interrogated and processed by the proces-
sor in the form of a clocked switching matrix. The positive pulses of
IC 403, inverted by means of IC 401, generated by pin 7 (Segment 1)
and pin 9 (Segment 2) serve as operating clocks. These pulses are
mutually offset by 3 ms (refer to pulse diagram). When a drive control
button is actuated the signal is pending at processor IC 403 as a HIGH
active pulse. When a new cassette is inserted -the contact RECORD
SAFETY (erasure block) opens = HIGH signal. Thus the processor
ignores the actuation of button RECORD.
The MEMORY switch (S 505) and the COUNTER switch (S 504) are
series-connected. If MEMORY is actuated and the counter reaches 000.
S 504 closes and transmits a LOW pulse via C 401 to pin 30 of IC 403.
The processor triggers the stop function.
DLL
If the cassette is removed during playback the DLL switches S 502 and
S 503, operating in parallel, dose. This signal — active LOW — reaches
pin 41 of IC 403 via D 401. The processor triggers the stop function.
This status is stored atter the cassette has been removed during PLAY
device function. Once the cassette has been inserted, switch CASSETTE
S 501, situated parallel to the DLL switches, opens and the previously
selected PLAY mode is reactivated. Switch S 501 closed = cassette re-
moved.
En d of tape switch-off
The information — tape running — is provided by a multi-pole solenoid
disc secured to the drive wheel of the counter at IC 501. This IC converts
the alternating magnetic fields into electric pulses. These pulses reach
pin 37 or IC 403 via R 422. The processor compares this tape running
frequency with the 1 kHz frequency of the oscillator IC 404 pending at
pin 22 (IC 403). If the tape running pulses feil to appear e.g. in the case
of a jammed cassette, STOP is released. In the case of tape running
disturbances the 1 kHz (5 %) frequency of the oscillator IC 404 should
be checked as this provides a reference frequency for the end of tape"
switch-off.
Outputs
The outputs for the device functions (solenoids and motors) are generated
by the processor as HIGH active. Let us take the course of signals for
PLAY as an ex anple. The active HIGH signal of the processor (pin 12,
IC 403) is routed to the base of 0407 via D 405 and R 423.0 407 be-
comes forward-biased and appl ies 0 V to the PLAY solenoids. At the
same time the HIGH signal routed from D 405 via R 420 and C 406 is
applied to the base of 0404. Transistor 0 404 becomes forward-biased
thus 0 405 becomes reverse-biased and 0 406 is fully forward-biased
with R 425. After approximately 600 ms (C 406) Q 404 becomes re-
verse-biased, Q 405 becomes forward-biased via R 424 and connects
the voltage divider R 426 to 0 V. Thus 0 406 assumes a higher resistance
and provides a retaining voltage for solenoid PLAY until the solenoids
are switched oft with a LOW signal Q 407.
In the case of solenoid RECORD an overvoltage (approximately 36V)
is applied, with Q 416, for a certain period (approximately 200 ms).
When the timer (C 424) preset time elapses 0 415 and 0 416 become
reverse-biased and thus the retaining function is taken over by Q 413.
This overexcitation ensures a quick and reliable response of the so-
lenoid.
The dynamic HIGH pulses generated by pin 14 to pin 20 (IC 403) are
converted into static HIGH signals by means of the D-latch IC 402. The
information item pending at the D-input is written in by means of a
HIGH pulse (approximately 10 ms) at the clock input pin 9 (IC 402)
and is available statically at the Q-output until a new information item
is stored.
Music finder
If the pushbuttons FF or REW are actuated during the play function,
the processor recognizes the music finder function and issues a LOW
signal at pin 31 (IC 403) = SCAN. This signal is routed via plug A to pin
9, enabling the finder amplifier. If a music gap is now recognized
(SPACE = LOW active, also refer to analog section) this LOW signal is
routed to the processor input pin 38 which activates the play function.
Autospace
The recording amplifier is muted by depressing the AUTO SPACE push-
button during the RECORD mode — HIGH signal from pin 32 (IC 403)
— the tape continues to run for approximately 4 s until the processor
stops the tape and releases RECORD STAND BY.
Record stan dby
The device switches into the RECORD STANDBY function when the
RECORD pushbutton is actuated and the RECORD safety contact
S 506 is closed (LOW at pin 36. IC 403) and this is indicated by the
flashing green LED PLAY. The solenoidsplay, FF/REW and record are
energized, muting of the playback branch is cancelled (clear muting
playback), the capstan motor is turned on, the real motor is turned off,
the recording amplifier is muted (MUTING RA = HIGH at Pin 32 1C403)
and the LED play flashes. If the PLAY pushbutton is now activated
the device is switched into the record function.
LED display
The PLAY. RECORD and REPEAT modes are each displayed by means
of an LED. The LEDs are driven on the cathode side by means of LOW
active segment pulses. The positive operating voltage is connected with
the transistors 0 401 and 0402 in the form of pulse. lf, for example,
the LED RECORD is driven, the processor generates the drive pulse for
0401 in phase with the pulses from Segment 1. Should LED REPEAT
light up however, the drive pulses for 0 401 are synchronous with the
pulses of Segment 2.
T = 12 ms
t = 3 ms
a= 6 ms
Pulse-Diagramm IC 403
o
I
Segment 1 7
Segment 2 9
Q401 Rec
28
Q401 Rep. ,
28
Q 401 Rec. + Rep 28
Q 402 Play
29
-411-
3 6 9 12 15 18 21 24 27 30 33
t(ms)
5