Technics QUARTZ SL-MA1 - Page 16

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Coil
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is “on” to apply
ated in the detec-
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al of comparator
1 turns “off’’ for
sith servo applied
Up
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5. Horizontal control circuit
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C201 path
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Q205
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Horizontal
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(Reference 7
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< Horizontal drive circuit >
In free mode (with arm on rest), microcomputer (IC401) pin @ is “H”, pin @) ‘‘pulse output”, pin @ “L”, then Q209
turns “on”, Q201 “off’’, Q205 “off’’, and analog switch (S1) is ‘‘on’’. (1C401 pin @) goes H’’ only in play mode, 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 is output to
1C201 pin @. (Vs is about 4V when IC401 pin @3) 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. The voltage is
amplified to apply servo to the horizontal drive circuit.
< Anti-skating >
In play mode, microcomputer (1C401) pin @ goes “H”, pin @ ‘‘pulse output’, pin @4 “H”, then Q209 turns ‘‘on”,
0201 “off”, Q205 ‘‘on’’, and analog switch (S1) is ‘‘off’, then 1C401 pin @) goes “H"”, Q212 “on”, Q211 “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 1C203 and
VR303 is in operation. The voltage Vx of VR303 and voltage Vo across the drive coil change linearly to Vx, therefore
voltage Vo is applied to the drive coil according to the variation of VR303 for the purpose of anti-skating.
< End detection circuit >
Vr
Horizontal
detection coil
Immediately after power “on”, the microcomputer pins @) and ®
delivers the outputs at the timing as shown on the right. 1C401
The output causes $3 to be shifted to R side, and the voltage is read Pin ®
into microcomputer pin @ . The value is the initial value. (Reading is (C08)
finished in about 1 sec.) pin@®
* Shifting it to R in the initial read mode is intended to avoid the (C09)
influence of external vibration of the detection coil, then the
resistance values of the coil and R are equal to each other. Pin @
After completion of read, S3 is shifted to the detection coil side. In
play mode, the change in voltage of the detection coil (inverse
electromotive voltage) caused by the movement of the magnet is
detected at 150° interval during a turn of the turntable platter, and the
input is entered into microcomputer pin @® .
When the slit plate under the tonearm comes to the return area, the
microcomputer detects the end through comparison between the initial
value and the inverse electromotive voltage of detection coil.
A/D
SL-MA‘1
Micro-
computer
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0.33 sec 0.33 se sec L
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