Supplyandtake-Upsensors; Safetytabswitch - Panasonic REV-1 Service Manual

8-3. Supply and Take-up Sensors
Supply and Take-up photo transistors are used to sense the beginning and
end
of a tape. The tape
has transparent leaders at the beginning and
end.
When these transparent leaders enter the tape transport path, they allow infrared light from the
sensor LED to reach either one of the tape end
sensors(photo-transistor).
If the Take-upend
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 activates the Stop mode and the Rewind
mode. The Rewind mode continues until the Take-up end sensor detects the end of the tape. The
tape beginning is detects by a low signal at SYSTEM CONTROL IC Take-up photo terminal. The tape
end is detected by a low signal at SYSTEM CONTROL IC Supply photo terminal.
If the light is received at both sensors at same time, the cassette is ejected.
<Operation after detecting the beginning and the end of tape>
Mode Detection of the beginning Detection of the end
Power off+on Short CUE Short REW
Cassette in Short CUE Short REW
Loading Short CUE Short REW
FF/CUE Auto REW
REW/REV
Short CUE
PLAY, REC Auto REW
I I
Timer REC
Power off
Both ends of tape detection (tape cut, no cassette),
(1) Cassette
in:
The cassette tape is 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.
8-4. Safety Tab Switch
A recorded video cassette can be protected against accidental erasure by breaking off the tab on the
cassette. The cassette 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 Safety Tab terminal. The
SYSTEM CONTROL IC will not go into the recording mode and automatically places the VCR in the
playback mode.
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