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How do VCRs recognize the beginnings/ends of tapes?

Discussion in 'Electronic Repair' started by Art Deco, Apr 19, 2006.

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  1. Art Deco

    Art Deco Guest

    Anyone know how this works? Is there a sensor that recognizes the
    transparent bits at the beginning and the end of a VCR tape?

    I have two Sony VCRs that upon rewinding come to a crashing halt
    rather than a smooth stop.

    Thanks for any advice/suggestions.
     
  2. VHS VCR's use the transparent tape at each end. Old style VCR's used a light
    bulbs and photocell. Newer ones most likley use an LED and some sort of
    photosensor. It should not be hard to find, it would be the only part
    that the tape goes through instead of over or around.

    Geoff.
     
  3. I.F.

    I.F. Guest

    If you look at the bottom of a VHS cassette, there's a hole near the flap
    halfway between the spools. The hole is for the "light tower" which is a
    plastic pillar with a LED (or bulb in older models) at the top. If you press
    the latch at the side of the cassette so you can lift the flap, this will
    expose a tiny slot at each end, there is usually a photo-diode at each side
    of the deck lift in the VCR.

    In older VCRs bulb failure was fairly common which was usually sensed by the
    microcontroller and caused the VCR to refuse to operate rather than work but
    fail to slow at the end of the tape. Most modern VCRs use the sensors under
    the spool drives to calculate the ratio of tape on the two spools and cut to
    a slower speed as it nears the end of the tape. If your lucky its these
    sensors causing the problem and they're opto-reflective types with just some
    dust to clean off - if they're Hall effect sensors you probably have a MPU
    fault!
     
  4. GregS

    GregS Guest

    Most should have speed sensors if a high speed rewind system is employed.
    This is in addition to the regular sensors. Its got to slow down before the sensor
    is set off or else banged tape or something bad.

    greg
     
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