Dual CS 741Q - Page 5

Via the analog switch IC
9007 pin 1/2 and resistor R 9030, the partial
voltage set with the pitch potentiometer P 33
and P 45 is additionally
applied to pin 5 of IC 9005, thus
making a speed alteration of ± 6 %
possible. In quartz
mode, the
pitch control loop is rendered
ineffective
by
opening 1C9007 pin 1/2.
Quartz
circuit
The
quartz circuit has the task of providing
the time
reference for
driving the
stroboscope and the phase comparator. By
means of the
phase
comparator, the speed control circuit
is
influenced in such a
way that a
closed phase control loop (PLL)
is produced which transposes
the position of the crystal oscillator on the speed.
The crystal oscillator,
consisting of T 9001, C 9001-3, R 9001, R
9002
and the crystal Q
9001, drives the programmable divider
IC 9001 at
pin 9. If the
speed selector is set to "33", the
input data P1 to Pg have
the bit pattern: LH
LLLH L H. This corresponds to the
decimal
number 162, with the significance of
P1 — Pg corresponding to the
numbers 1, 2, 4, 8, 16, 32, 64 and 128.
When the selector is set to
"45", the deci mal number 120 is represented by the bit
pattern (P1 — Pg)
L LLLLLH H. In this
case, due to pin 2, the significance of P1 to Pg
is as follows: 1, 2, 4, 8, 10, 20, 40 and 80. The frequencies 28.44 kHz
and 38.40 kHz are now available at the output pin 15 for further fre-
quency duration. The frequencies 111 Hz
and 150 Hz are generated by
IC 9003 with eight stages
and these precisely correspond to
the control
frequencies
for the speeds 33 and 45 rpm. Via
the inverter IC 9006
pin
11/10, the phase comparator, consisting of the two D flip-flops in
IC 9004 and R 9010
and D 9001, is
driven
with the set
frequency. lt
receives the actual current speed via inverter IC 9006
pin 1/2 from pin 1
of IC 9005. Via the phase angles from —360 to +360, the
information is
applied in the form of variable pulse widths at outputs pin 13 and pin 2
of
IC 9004. These
signals are decoupled by diodes D
9002 and D 9003
and
matched
with R
9011 and R
9012 to the control
circuitry in such a
way that a
synchronous holding range from —5% to +2 % is obtained.
Synchronization is achieved by the fact that a positive current
flows
through R 9011 to the speed determining capacitor C
9015 in the event
of a leading phase angle.
This reduces the sawtooth voltage
(measured
from + 12 V), resulting in a
decrease in the motor current. If the phase
angle
lags, a negative current flows
through R 9012 to C 9015,
resulting
in an
increase in the motor
current. These
decreases and increases result
in
stabilization of the
preset speed.
Start -up
synchronization
If the motor current increases
too much due to an increased torque load
or during start-up, the start-up synchronization is activated due to the
voltage
drop at R 9044 via T 9007 and IC 9006 pin
5/6, and
diode
D 9005 is caused to block. The generator pulses at IC 9005 pin 1 are
differentiated by C 9007 and R 9005 after the
inverter IC 9006
pin 1/2
and, via R 9006, these pulses reach the reset input of the quartz divider
whose
output frequency runs synchronously with the
generator
frequency
as the result of
this. Thus, there is no
speed
modifiying signal at the
out-
put of the phase
comparator and, as the result of this, the
drive
locks in
exactly the nominal speed. As the voltage drop at R 9044 now disappears,
pin 6 of IC 9006
pin 5/6 becomes low, D 9005
becomes conductive and
the start up synchronization is deactivated. Via the phase comparator,
the speed is
now kept phase-rigid by means of
the quartz divider
which
is now
running
freely.
Stroboscrope
The precise
crystal-controlled output frequency
of divider IC
9002 is
differentiated by R 9009, C 9008 and R
9013 and,
via diode D
9004,
routed
to the base of T 9002. This briefly becomes
reverse-biased and,
at the base of T
9003, a voltage
sets in which is generated
by resistors
R 9014 and R
9015 wired as a voltage divider.
This base
voltage now
causes T
9003 to become conductive until a voltage appears at
the emit-
ter resistor R
9016 which is approximately 0.7 V lower than at the base.
As the base voltage
is constant, the voltage at R 9016
is also
constant
and, as the result
of this, the collector
current is almost independent of
the load
resistance (LED voltäge). The stroboscope
LED's thus light up
with a constant
pulse-shaped
current in which case their "on" duration
mainly
depends on C 9008 and R 9013. At 33
rpm, the repetition fre-
quency is 55.5 Hz and, at 45 rpm, the frequency is 75 Hz
and is precisely
crystalcontrolled.
Motor bridge
output stage
and power
supply
The following
circuit is
accommodated on a separate printed
circuit
board. The communtation
transistors T 9201 to T 9204 are
alternately
driven by the hell generator
in the motor, as the result of which
they are
forward-biased to a greater or lesser
extent depending on
the drai n-source
resistance
of T 9008.
Accordingly, via
resistors R 9202 — R
9205,
the
corresponding PNP transistors T 9205 —
T 9208
become
conductive,
resulting in a
bridge
arrangement. The
transistors T
9201 and T 9206,
T 9202 and
T 9205, T 9203 and
T 9208, T 9204 and T
9207 are then
switched in pairs. C 9202 and C 9203
prevent steep
current edges
during
switchover of
the bridge. The hall
generator voltage is
produced by
R
9201 and the 1.1 kOhm
resistors in the motor.
Transistors T 9201 —
T
9204 are screwed onto
a heat sink, also
accommodating the
voltage
controllers for
the control circuitry, for better heat
dissipation. C
9201
and C
9204 suppress
the inclination of the controller
circuitry to
osci I late.
Display
The
display serves
to
visually indicate the
following
conditions:
33 and 45 rpm
speed display, quartz or pitch
mode and display of the
pitch
deviation in %. The two LED's
for the 33 and 45 rpm
speed indi-
cation light
up alternately
depending on the switch
setting.
If there is an excessive
torque load on the platter, and in the start up
phase, the anode potential is connected to ground by T 9301,
as the
result of which
they are extinguished.
The two LED's for
quartz or pitch mode also
light up depending on the
switch setting S 2. When the switch S 2 is set to „quartz", the LED's of
the
pitch display
are blanked
additionally by D
9307 and IC
9301. This
is also the case in the start up phase and when the platter is braked
extremely.
IC 9301, and thus the LED
scale, is
driven with the pitch
control. lts
voltage range
from 0 . . . 12 V corresponds to the
range of the LED
scale from —6%
to
+6%.
Distributor board
The printed circuit board comprises the rectifier circuit D 9451 —
D 9454, the RF filters C 9451 and C 9452 and the 100 Hz filter consi-
sting of C 9453. In addition, the pc board serves as the
central wirding
board.
The
front controls,
the solenoids and the
micro
switches are
wired here.
Start function
The start solenoid M 1 is energized when the start button S 4 is depres-
sed. I ts
seit
holding contact S 12 holds the
magnet in operating position
via D 9456 and T 9451.
The motor circuitry is switched to 0 V via
D
9455. lt the cam
wheel then clicks through, the drive switch S
8 is
activated. The motor
circuitry is now completely connected to
ground.
Briefly
before the cam wheel moves to its
zero position, it pushes back
the armature of the
start solenoid M 1 and the solenoid is
deenergized.
lf, at the beginning of the start
phase, the cam of the motor pinion is in
such an unfavorable position that the armature of
the start solenoid can
not
completely push forward the
switch off mechanism,
and
the motor
can not be
started, as the armature does not
reach holding contact. In
order to prevent this, the motor circuitry
receives current via D 9461 in
this case. The motor starts to turn and the start
procedure runs pro-
perly.
Continuous
play function
The continuous play button S 3 has a locking function. lt can be un-
locked by pressing it once again or by depressing the stop button S 5.
The continuous play button connects the start solenoid M 1 to the
„continuous
play" cam switch S 9 in such a way that the start function
and not the stop
function is
triggered oft after a record has been
played.
Stop function
For
the
stop
function, the
start solenoid M
1 must only remain in
its
operating position for a
short time
(maximally 1/4 of a
cam rotation).
If it remains in
function for a longer
time,
the
deflection segment of the
cam
thweel is actuated.
This then corresponds
to the start
function.
In order to
ensure that the
self-holding
contact S 12 of the
solenoid
M 1
is released, the
distributor boards
contains a circuit
which briefly
keeps current from
the solenoid
M 1 after the
stop button S 5
is re-
leased
or, at the
latest, when the cam
wheel-continuous play switch
S 9
is switched over.
Normally, this
interruption circuit conducts a
current. The base of
T 9451
is kept at
positive potential viä R
9452. If the stop
button S 5 is
depressed, capacitor C
9454 is
discharged via R
9453. After the
start
button is
released or after
switchover of
the cam switch
S 9, C 9454
can
charge up via R
9452. In
this way,
transistor T 9451
remains
reverse-
biased
until its switching
threshold
of approximately 5
V is reached.
During this
period, the
armature of the
start solenoid
M 1 must be
de-
energized so
that the stop
function can
operate
properly.
This
time
amountes to
0.075s
to 0.3 s.
Diode
D 9459 permits
energization of
the start solenoid M 1 when stop
is actuated.
The diode D
9460 prevents C 9454 from charging
up via the branch of
D
9459. C 9454 should charge
up via R 9452.
D 9456 additionally increases the emitter potential to ensure proper
operation.
D 9455 prevents
response of the start solenoid when the unit is swit-
ched on
manually.
D 9457 and D 9458 suppress negative peak voltages at the solenoids du -
ring switch
oft.
Muting
The AF-signal is fed from
the cartridge to the muting switch S 11,
which is open in the basic position of the cam. The
contacts of the
muting relay RL 9401 is
parallel with the switch S 11.
This relay is
driven via the switches S
4 — Start, S
9—
Continous Play
and S6 — Lift.
The relay is closed for approx. 1.2
seconds.
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