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PA3010
1 . 4 T A P E L E A D E R D E T E C T O R C I R C U I T
The tape leader detection circuit functions in
the auto-reverse mode to detect the point of
transition from the coated portion to the leader
portion of the tape. It then directs the mechanism
to reverse the direction oftravel, or places the unit
in a STOP status when this event occurs from the
fast-forward (FF) or rewind (REW) mode.
The detector uses an optical system based on an
infrared LED whose emission is picked up by a
phototransistor. The circuit is activated by detect-
ing a difference in the amount of light passed by
the coated portion of tape, and the amount passed
by the transparent leader.
The output from pin 16 of PA3010 is converted
to light by the LED, and passes through the path
shown in Fig. 1-13 to be picked up by the photo-
transistor. During tape travel, the amount of light
received by the phototransistor is quite small, so
the input level at pin 7 is held low. This causes
the charge and voltage at pin 3 and 4 to also be
held low, presenting a low logic input to the + and
- terminals of comparator. This results in a low
output from pin 2. But as the transparent leader
pil$es into the light path, the amount of light
picked up by the phototransistor
suddenly in-
creases the input to pin 7. This causes pin 3 to snap
high, consequently applying a high input to the +
terminal of the comparator. Output from pin 2
then goes high. As pin 3 goes high, the capacitor
connected to pin 4 starts charging, raising the
input level to the -
terminal of the comparator.
When the level of the - terminal reaches that of
the + terminal, the output from the comparator
snaps from high to low, and the output pulse
taken from pin 2 appears as shown in Fig. 1-1b.
CPU PD 6006 uses this output pulse to control
the various mechanisms performing the mecha-
nical functions
of auto-reverse and automatic
stop.
L E D
_
R E F E R E N C E P I N
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TAPE
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Fig. 1-13 Tape leader detector section
. P H O T O T R A N S I S T O R
Fig. 1-14
Tape leader detector circuit
P I N
N O
t 6
4
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o
B
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C O A T E O T A P E
L E A N R
T A P E
Fig. 1- 1 5
Tape leader detector waves
1 . 5 E N D S E N S O R C I R C U I T
Since CT-9R and CT-8R are equipped with a
tape leader detector circuit, they go into a STOP
status or go through a direction operation before
reaching the point where t,l-e end sensor cirucit is
activated, so normally the end sensor circuit will
not operate. However, where there is no leader on
the cassette tape, or where there is an insufficient
difference
in the infrared
transmission factor
between the coated portion and leader portion of
the tape, or in case the reel motor stops rotating
before the tape leader is detected, the end sensor
circuit is then activated.
When the reel motor starts tuming, a sensing
pulse is transmitted from pin 13 of IC PA2010
(used to control the reel motor) to pin 88 of
PD6006. (This pulse is taken from the Hall element
and shaped into a squaxe wave by PA2010.)
When this pulse is maintained at either a low (L) or
high (H) level for a period exceeding three seconds,
PD6006 interprets that to mean the end of the
tape and thus switches to the next mode of opera-
tion.
l 4
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