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Optical information processing apparatus in which the output of an optical sensor is replaced by a reference signal during the occurrence of malfunction

Image Number 3 for United States Patent #5151888.

An optical information processing apparatus effects recording and/or reproduction of information by scanning information tracks of an optical recording medium by at least one condensed light beam while effecting tracking and/or focusing control. The apparatus comprises at least two groups of optical sensors for receiving the light of the light beam reflected. By the medium, a circuit for producing a signal for effecting the control from the output of each of the groups of optical sensors, a reference signal generating source, and a switching circuit for causing, when at least one of the outputs of the groups of optical sensors exhibits an abnormal value, the reference signal, instead of the at least one output, to be input to the control signal producing circuit.

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