Pictured above are the three most common ways that the VCR detects problems rotation. Starting with the capstan motor in the top left. Most all of the flat (pancake) capstans use a Hall effect sensor or a DME to detect and control rotation. The sensor is named after Edwin Hall who discover the perpendicular magnetic field conductor. The DME stands for Dividing type Magnetic resistance Element. It is the component in the circle and enlarged lower left. Both type sensors have the property of fluctuating a current whenever it comes into close proximity of a rotating magnetic field. So what you see as the dark gray ring running around the outer perimeter of the rotor is a sequence of magnets with north and south poles or fields. This is illustrated by the white drawing upper left. Now if you have a fluctuating field as the capstan is rotating then all you need is a circuit that counts the change. This information can be used for speed detection, regulation and direction indication. So with this type of capstan the sensor is not only used to reference and regulate the various speeds required, it also detects if it is moving. If it discovers that it isn't the machine shuts down all mechanical operation in order to prevent damage to the tape and the machine. In some models the capstan is turned during loading and if no rotation is detected the operation will reverse and the cassette will be automatically ejected. But this isn't the only way to test tape movement. Two more types are used for reel rotation and they are shown on the right. This time in the top example a light emitting diode is mounted across from a detection sensor. This is commonly called an opto sensor, short for optical detector. How it works is a series of slots on the bottom of the reel passes between the LED beam and detector. The calculating IC keeps tabs on the timing between blanks. In the example lower right reflective bars on the reel supplies sampling. The system software is always counting and comparing the inputed signal to the accepted program standard. Any error signal there is a problem. It depends on the type of unit for which safeguards are implemented. This timing countdown method is used for a number other operations, such as in cassette loading. If loading doesn't complete within a predetermined time, it reverses and ejects the cassette out of the VCR. Same goes for threading the path. Aborting loading or threading can be caused by a number of things. The tape could be out of place in the cassette. One of the reels might be unable to move or the video drum isn't rotating, or the capstan could be locked up, just to name few. Usually the only buttons that function after a rotation failure are eject and power on/off. There is one last item I want to cover before we move on to the actual alignment and that is proper lubrication, click here. To go back to the previous window click here ©Misterßetamax go to homepage