Technics QUARTZ SL-MA1 - Page 15

4. Vertical control circuit
< Operating principle >
When a magnetic field is created by a disk magnet of arm
drive DD motor, thereby letting a current flow in the coil
wound in a circular from, then vertical forces are generated
in either direction (Fleming's left-hand rule). Since the coil
is secured on the main body, the magnet rotates on the
fulcrum in the direction of the arrow due to the reaction.
The rotation is utilized for cueing operation.
Direction
of current
Back yoke
Vr (Reference
Det.
Amp.
voltage)
1€301
Vertical
detection coil
Cueing
| Magnet
Vertical !
drive
coil
a---
Cueing
Saray To muting
- brake control
< Vertical drive circuit >
During
cueing-up,
microcomputer
(1C401)
pin
@
goes
L"
and
0304
turns
‘‘off”,
then
the
potential
of
comparator
(1C301)
pin
@
rises
to
become
©
>
@
and
the
output
of
pin
()
becomes
“—"’.
As
pin
@
is
“—",
Q301
turns
“on’’
to
apply
voltage
to
the
drive
coil.
When voltage is applied to the drive coil, the magnet begins rotating (vertically) causing voltage to be generated in the detec-
tion coil. The voltage is input to comparator pin (2 through the amplifier thereby applying vertical drive servo.
During cueing-down, microcomputer (1C401) pin @ goes ‘‘H’”” and Q304 turns “on’’, then the potential of comparator
(1C301) pin @ lowers to becomes @ > © and the output of pin @ becomes “'+’’. As pin @ is +", Q301 turns “off” for
a moment, causing the voltage of drive coil to drop abruptly.
When the voltage of drive coil is decreased, the magnet begings to rotate downward, but is slolwy returns with servo applied
due to the voltage generated in the detection coil.
@ Voltage of @ point
Down Down Up Up
u
iti
d
H
>
command
completed
command
completed
= Stylus position etection i Bae Up os
Since the cueing speed is controlled as mentioned above, 12V motion } Play } motion 1I2V
the
voltage
applied
to
the
drive
coil
changes
as
illustrated
Oieaks
on
the
right
according
to
the
load
in
cueing
mode.
The
disc
position of the stylus on or off the disc is detected by the
voltage for the operation of brake (to prevent the stylus
from dropping aslant) and muting.
Ov
ey
@and@...... stylus pressure and magnet loads.
@ and @)...... only magnet load.
5. Horizontal control circuit
Vr
C201 ican
f
2
et
as
Horizontal
2 Ro 4 detection coil
5V 12V Ey sn
|
1c40l
S|
ron Me |
id!
Lead-in
}....‘on’”
M
F
E02 Qa) () ra ie Return Servo amp. cS aan
Free Play “oft 1C203 |
Lead-in - ...."L” Q205 fo
Return |
PAV
sc
cececee
s
3
Horizontal
drive coil
Free }
Play frcccee
Lead-in }
Return
Free } oY
Play f°" 0 1C203
8 Driver Le 20!
Lead-in...... ‘“ Vr
Return....... Vr
(Reference 7
voltage)
Vr cA Q2il
Eree
oe
Q2i2
KC)
Reference
voltage
Lead-in?..... (> generated
Return coioG) ic)
Piavs ceca ausd “H"
< Horizontal drive circuit >
In free mode (with arm on rest), microcomputer (1C401) pin @2 is “H”, pin @) “pulse output”, pin @ “L”, then Q209
turns “on”, 0201 “off’’, Q205 “off, and analog switch (S1) is ‘‘on’’. (IC401 pin @) goes “‘H” only in playmode, and
analog switch S2 is ‘‘off’’.) In this case, the voltage Vo across the horizontal drive coil is ‘‘0’’.
During lead-in mode, microcomputer (1C401) pin @ goes “L”, pin @) “H’’, pin @ “L”, then Q209 turns ‘off”’, Q201
“on”, Q205 “off, and analog switch (S1) is ‘‘on’’. Also, speed (rotational direction) command voltage Vs i; output to
1C201 pin @. (Vs is about 4V when 1C401 pin @) is at “H’’, and about 8V at “L”.)
Due to the voltage of Vs, the voltage across the drive coil instantaneously changes from ‘0’ to plus (+) voltage causing
the magnet to start rotating. Then a voltage is generated in the deteciton coil, and the voltage is amplified to apply servo
to the horizontal drive circuit. Vo is almost zero while servo is applied to the circuit.
In return mode, microcomputer (1C401) pin @3) goes ‘‘L” and the speed command voltage Vs becomes higher than in
lead-in mode (about 8V), and the voltage across the drive coil instantaneously changes from “0” to minus (-) voltage.
The magnet starts rotating in the reverse direction causing a voltage to be generated in the detection coil. Tre voltage is
amplified to apply servo to the horizontal drive circuit.
< Anti-skating >
In play mode, microcomputer (1C401) pin @ goes “H”, pin @3 ‘pulse output”, pin @ “H”, then 0209 tirns “on”,
Q201 “off’’, Q205 “‘on’’, and analog switch (S1) is ‘off’, then 1C401 pin @) goes “H”, Q212 “on’’, O211 ‘off’, and
analog switch S2 is “on’’. ,
That is, the servo circuit by the detection coil becomes open, then only the horizontal drive circuit consisting of|\C2203 and
VR303 is in operation. The voltage Vx of VR303 and voltage Vo across the drive coil change linearly to Vx thwerefore
voltage Vo is applied to the drive coil according to the variation of VR303 for the purpose of anti-skating.