Optical storage disc scanner with improved scanner positioning

An optical scanner for scanning a record carrier having a track defining a longitudinal tracking direction, wherein the track has an asymmetric property transverse to the longitudinal tracking direction, the asymmetry corresponding to an information signal, and the scanner comprises:

• a radiation source for generating a radiation beam,
• a radiation-sensitive detector having first and second portions located on opposite sides of a line corresponding to the longitudinal tracking direction, and means for deriving a first and a second detection signal which are indicative of the power of radiation impinging on said first and second portions respectively,
• an optical system for directing said radiation beam, via said record carrier, onto said detector, said radiation beam producing a radiation spot on said record carrier,
• means for causing said radiation spot to scan said track on said record carrier in the longitudinal tracking direction,
• signal combination means for deriving a difference signal indicative of the difference between said first and second detection signals, and
• an information regaining circuit for deriving information defined by said difference signal,
• characterized in that the means for causing operates independently of said difference signal, and the signal combination means further comprises:
• a balancing circuit for weighting the respective contributions of said first and second detection signals to said difference signal according to a weighting ratio,
• means for determining the DC component value in the difference signal derived from the weighted first and second detection signals, and
• means, operable while said means for causing is operative, and responsive to the DC component value in the difference signal determined by said means for determining, for setting said weighting ratio to a value at which the DC component value is substantially zero.