Circuit Descriptions - Pioneer PL-L50 Service Manual

5. CIRCUIT DESCRIPTIONS

5.1 CIRCUIT DESCRIPTIONS
5.1.1 Address Sensor Circuit
The address sensor is located on the mechanism base
unit. It detects the position of the tonearm and sends ad­
dress pulses to the control IC as the tonearm moves. The
address sensor is made up of an internal schmitt trigger
circuit photo interrupter and a slit wheel which is syn­
chronized with the carriage. The slit wheel spins when the
carriage moves and intermittently cuts off I ight to the
photo interrupter (0301) in pulses which correspond to
the carriage movement. These pulses are counted by the
control IC, which detects the distance the carriage moves,
the tonearm lowering position and the end of the record.
It also registers band addresses.
The address pulses from the photo interrupter work
as follows: When the light is cut off, the output is "L,"
and when the . : ight is not cut off the output is "H." One
address signal pulse is approximately equivalent to 0.114 mm
of tonearm movement.
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Photo interrupter
Fig. 5-1 Address Sensor Circuit
5.1.2 Tracking Sensor Circuit
This circuit detects tracking errors by means of a shutter
which is synchronized with the tonearm and a photo in­
terrupter.
The tracking sensor is made up of a shutter synchro­
nized with the tonearm and a photo interrupter which is
mounted onto the carriage base board. When the tonearm
lowers and begins tracing the record surface the tonearm
tracking errors increase as the number of rpms increases.
When tracking errors increase, the shutter, which is syn­
chronized with the tonearm, also moves and the light cut­
off rate of the photo interrupter changes. Subsequently, the
output of the photo interrupter changes and is sent to the
tonearm drive unit in the form of tracking error signals.
Voltage regulator
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Slit wheel
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drive motor
Fig. 5-2 Tracking sensor circuit
Sensor
utter
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Tracking error
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Tracking error
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Fig. 5-3 Detection of tracking errors.
VR201
Tracking sensor
gain ADJ
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