Dual C 824 Serviceanleitung Seite 5

Device control
Processor
Reset
Inputs
The MEMORY switch (S 505) and ine COUNTER switch (S 504) are
series-connected. If MEMORY is actuated and the counter reaches 000,
S 504 closes and transmits a LOW culse via C 401 to pin 30 of IC 403.
The processor triggers the stop function,
"DLL
lf the cassette is removed during cieyreck the DLL switches S 502 and
S 503, operating in parallel, close. Tris signal — active LOW — reaches
pin 41 of IC 403 via D 401. The crocessor triggers the stop function.
This status is stored after the cassette has been removed during PLAY
device function. Once the cassette "es seen inserted, switch CASSETTE
S 501, situated parallel to the DLL switches, opens and the previously
selected PLAY mode is reactivatec. Sivitch S 501 closed = cassette re-
moved. :
End of tape switch-off
The information — tape running — is crovided by a multi-pole solenoid |
disc secured to the drive wheel of the counter at IC 501. This iC converts
the alternating magnetic fields inca 2iectric pulses. These pulses reach
pin 37 or IC 403 via R 422. The srocessor compares this tape running
frequency with the 1 kHz frequency of the oscillator 1C 404 pending at
pin 22 (IC 403). If the tape runnire oulses fail to appear e.g. in the case
of a jammed cassette, STOP is reeesed. In the case of tape running.
disturbances the 1 kHz (5 %) frequency of the oscillator !C 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 Q 407 via D 405 and R 423. Q 407 be-
comes forward-biased and applies O V to the PLAY solenoids. At the
same time the HIGH signa! routed from D 405 via R 420 and C 406 is
applied to the base of Q 404, Trensistcr Q 404 becomes forward-biased
thus Q 405 becomes reverse-biased and Q 406 is fully forward-biased
with R 425. After approximately GOO ms (C 406) Q 404 becomes re-.
verse-biased, Q 405 becomes forvard-biased via R 424 and connects
the voltage divider R 426 to 0 V. Thus O 406 assumes a higher resistance
and provides a retaining voltage for solenoid PLAY until the solenoids
are switched off with a LOW signal OQ 407.
in the case of solenoid RECORD an overvoltage (approximately 36 V)
is applied, with Q 416, for a certain period (approximately 200 ms).
When the timer (C 424) preset time elapses Q 415 and OQ 416 become ©
reverse-biased and thus the retaining function is taken over by OQ 413.
This overexcitation ensures a quick and reliable response of the so-
lenoid.
The dynamic HIGH sues 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-cutput 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.
Autos pace
Record standby
The device switches into the RECORD STANDBY function when the
RECORD pushbutton is actuated and the RECORD safety contact
flashing green LED PLAY. The solenoids play , FF/REW. and record are
energized, muting of the playback branch is cancelled (clear muting
playback), the capstan motor is turned on, the reel motor is turned off,
the recording amplifier is muted (MUTING RA =HIGH at Pin 32 IC 403)
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 Q 401 and O 402 in the form of pulse. If, for example,
'the LED RECORD is driven, the processor generates the drive pulse for
Q 401 in phase with the pulses from Segment 1. Should LED REPEAT
light up however, the drive pulses for Q 401 are synchronous with the
pulses of Segment 2.
Pulse-Diagramm IC 403
T=12 ms 2 ol
t 3 ms Ny a
a= 6ms = t
=
Segment 1........... 7
Segment 2..........9
Q 401 Rec......... 28
Q 401 Rep......... 28
© 401 Rec. + Rep. 28
Q 402 Play rae 29
3.6 9 12 15 18 21 24 27 30 33
t(ms)