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10.3. SUPPLY AND TAKE-UP SENSORS
Supply and Take-up phototransistors are used to sense the beginning and end of tape. The tapes has transparent leaders enter
the tape transport path, they allow infrared light from the sensor LED to reach either one of the tape end sensors
(phototransistor).
If the Take-up end sensor detects the light, the microprocessor SYSTEM CONTROL IC places the VCR in the Stop mode and
then performs a short Cue.
If the supply end sensor is triggered, the microprocessor activated the Stop mode and the Rewind mode.
The Rewind mode continues until that the Take-up end sensor detects the end of the tape. The tape beginning is detected by a
low signal at SYSTM CONTROL IC Supply photo terminal.
If the light is received at both sensors at same time, cassette is ejected.
10-3-1. Detection timing
Start and end edges are detected in VCR mode when capstan rotates and mechanism shifts its position. LED always lights
during power on.
10-3-2. Sensitivity of detecting the start and end edges of tape
1.
Transparent tape that has more than approx. 50% transparency according to VHS standard is detected.
2.
Tape that has less than approx. 3% transparency according to VHS standard is not detected.
10-3-3. Action after start and end edges are detected
Mode
POWER OFF
ON
CASSETTE IN
LOADING
PLAY/REC/CUE/FF/SLOW/STILL/ADUB/I
NSERT
RPLAY/REV/RSLOW
REC PAUSE SHORT REW
TIMER REC/OTR
AV2PB(H) REC
PLAY OFF TIMER
*1: SHORT CUE is to shift to STOP after rotating the tape until white part of tape is over. When other mode such as PLAY is set
during detecting the start edge, mode shift to the required mode after the white part of tape is wound.
*2: SHORT REW shifts to STOP or POFF after REW is performed for approx. 2 sec. in actual time.
Both ends of tape detection (tape cut, no cassette)
(1) Cassette in: The cassette tape id ejected
(2) Other mode: The unit goes to Stop mode and it is impossible to operate except eject key.
(3) Timer REC: Power is turned off after short CUE is performed.
10-4. SAFETY TAB SWITCH
A recorded video cassette tape can be protected against accidental erasure by breaking off the tab on the cassette tape. The
cassette tape can now only be used for playback. To be able to record on the cassette, cover the hole with adhesive tape. If the
safety tab on the cassette has been removed, Safety Tab Switch is off (open) and high signal is supplied to SYSTEM CONTROL
IC will not go into the recording mode and automatically place the VCR in the playback mode. If trying to set REC, ADUB or insert,
cassette mark flashes to warn.
Detection of the start
Detection of the end
edge
edge
SHORT CUE *1
SHORT REW *2
SHORT CUE *1
SHORT REW *2
SHORT CUE *1
SHORT REW *2
--------------
AUTO REW
SHORT CUE *1
---------------
--------------
---------------
--------------
SHIRT REW *2
--------------
AUTO REW
47
Detection
edges
STOP
EJECT
STOP
STOP
STOP
STOP
STOP or P-OFF
POWER OFF
STOP or P-OFF
POWER OFF
of
both
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