How do VCRs recognize the beginnings/ends of tapes?

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.

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!

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