Marantz CD-73 - 3. DRAWER MOTOR CONTROL P.W. BORAD WORKING PRINCIPLE; 3.1 Drawer Motor Drive Circuit; C. Explanation of overall operation

3.
DRAWER
MOTOR
CONTROL
P.W.
BORAD
WORKING
PRINCIPLE
Drawer motor control P. W. Borad includes the following.
(1) Drawer motor drive circuit
(2) Remote control circuit (Marantz Bus System decoder
circuit)
3.1 Drawer Motor Drive Circuit
A. Outline of the system
This circuit revolves and reverses the drawer motor by
the OPEN/CLOSE switch of S802 on the front panel to
open and close the drawer. It includes a circuit to
increase starting torque and a safety circuit which stops
automatically when something is caught in the drawer.
B. Operation of each part
a) Q809, Q808 and Q807 are motor drive circuits.
Especially Q808 increases motor starting torque.
b) When the voltage of R820 becomes over about 0.6V,
the base current begins to flow through Q803. That
is, the motor is locked to detect the excessive current.
c) Q805 and Q806 make up a set/reset flip flop, which
is set whell positive voltage is put into the base of
Q805. And it is reset when the base becomes 0. As
long as it is set, D806 is ‘ON’ and motor drive circuit
does not operate.
d) Q802 becomes “ON’’ just for--a few msec when the
OPEN/CLOSE switch of S802 is pushed. (S802 is
non-shorting type.)
OPENSCLOSE
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e) Q801 becomes “ON’’ just for the time-constant t4
based on R816/R801/C801only afterS802 is changed
from CLOSE to OPEN, and makes the base of Q809
OV to stop the motor drive circuit.
Meanwhile, the voltage of C807 is discharged to
increase the torque for the time-constant t of C807/
R822 just after the end of ty.
. Explanation of overall operation
a) During the shift of OPEN/CLOSE switch S802, from
OPEN to CLOSE, Q802 becomes “ON” in an instant
and flip flop which is composed of Q805 and Q806
is reset to cut off D806.
b) Consequently motor drive circuit which is composed
of Q809, Q808 and O807 begins to operate to switch
on the drawer motor.
c) When the drawer comes to the mechanical end,
short-circuit current begins to flow to the motor to
generate voltage of R820 about 1V. This voltage
reverses Q803 to cut off D804.
After D804 is cut off, C805 is discharged through
R807 and Q804, and Q804 becomes OFF after about
2.5 sec.
As a result, the collector voltage of Q804 rises to set
the above flip flop through R809/R810. In this way,
the motor drive circuit becomes OFF again.
f) You have the same operation also when S802 is
changed from CLOSE to OPEN. But Q801 has been
added so that Q808 which increases start up torque
can become ON without fail.
d
e
CLOSE>OPEN
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Q802 Collector | | if | |
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Motor Current
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R820
Voltage
ae
CLOSE Joo nm a
Position
DRAWER
Position
OPEN
Position
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