Pioneer FX-K99DK WG Service Manual page 29

Although the widths of the first and second pulses remain
unchanged if motor rotation is speeded up, the Schmidt
~ circuit output pulse frequency is increased. In other words,
since the first and second pulse cycle periods are reduced,
the S2 OFF interval is shortened. This means that C12 is
discharged for a shorter period of time,and the resultant
higher voltage is transferred to C9.
Since negative characteristics apply between pin 11 and the
motor pin, an increase in the C9 voltage results in the
motor speed being decreased, thereby enabling the speed to
be controlled.
To prevent CQ discharging beyond pin 11, the discharge
voltage is passed through a high impedance buffer section
and through to a comparator amplifier. With a reference
voltage of Vcc/2 in the comparator section, the inverted
input voltage is compared, and any increase or decrease in
voltage is used to contro! the motor speed.
If the inverted input voltage is greater than the reference
voltage, a negative voltage is applied to reduce the com-
parator output current, thereby slowing down the motor
speed. Hence, since the motor will operate at maximum
speed if the C9 charging quantity (comparator inverted
input) is 0, there is no need for a special activator circuit
when the power supply is activated. The amount of charge
on C9 is about Vcc/2 when constant tape travel speed is
reached.
Rpm speed can be adjusted by VR1. If the resistance is
lowered, the C5 charging time constant is decreased,
resulting in S2 being ON for a shorter period of time (and
being OFF for a longer period of time). Therefore, a
smaller charging voltage transferred to C9, and the motor
speed is subsequently increased.
9.19 PROTECTOR CIRCUITS
Protector circuits are used to guard against the following
five problems.
1. If the tape should happen to break during PLAY mode
and reel motor "runaway" condition is detected, tape
operations are stopped for two seconds before switching
to ATSC operation.
2. If the ATSC operation is not completed within ten
seconds, ATSC is suspended and tape operations are
halted. The cassette tape is then ejected, and normal
operation can be resumed if another cassette tape is
loaded. ;
3. If the end of tape is detected four times within ten
seconds, the deck is stopped to protect the mechanism.
Normal operations can be resumed by pressing the TAPE
button.
4. Transmission data error detection
The system featured in this deck involves constant
transfer of data between four ICs.
If noise is generated in the data transmission line result-
ing in data transfer error, the deck and tuner are both
stopped for two seconds and then restored to the
condition prior to the generation of noise.
Note: If the deck or tuner is switched to scanning,
frequency UP/DOWN, start of tape search etc just
before generation of the transfer error, that selected
operation is not restored after the two second stop.
Instead, the deck is restarted in PLAY mode, and the
tuner is returned to "last direction" reception.
5. If cassette loading or unloading operation takes more
than the normal two seconds, the current operation is
reversed (that is, unloading -is_ changed to loading,
and loading is changed to unloading). If the cassette
is caught somewhere, and neither ejection nor insertion
is possible after switching to loading and unloading
mode three times, the deck is stopped.
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