Method of locating and inspecting dropouts on a magnetic disc

Claim 1

A method of selectively inspecting a magnetic disc in those locations where dropouts in the form of loss of magnetic signal intensity of information recorded thereon have been detected comprising the steps of: detecting dropouts on the disc by: rotating the disc at a substantially constant angular velocity while recording a magnetic signal of constant intensity along predefined concentric circular tracks rotating the disc at the same substantially constant angular velocity while reading the recorded magnetic signal along said predefined tracks comparing the intensity of the read signal with a predefined threshold to detect a level of loss of magnetic signal intensity rotating the disc at the same substantially constant angular velocity while reading the recorded magnetic signal along said predefined tracks comparing the intensity of the read signal with a different predefined threshold to detect another level of loss of magnetic signal intensity determining the angular position of detected losses of signal intensity by: measuring a first time interval between passage of a synchronizing signal on the disc and each detected loss of magnetic signal intensity measuring a second time interval between passage of said synchronizing signal and subsequent second passage of said synchronizing signal and dividing the first time interval by the second time interval and multiplyinq the resulting quotient by 360 to precisely define the angular position of each dropout in degrees storing information as to such detected losses of magnetic signal intensity in a computer, generating a map of the disc with the levels of losses of magnetic signal intensity color coded displaying said map on a color CRT display device and moving the disc into operative relationship with a disc inspecting instrument, and controlling the position of the disc with respect to such instrument on the basis of said detected signal loss location information stored in the computer, so that specific dropouts may be selected for inspection by positioning a cursor over the color coded symbol representing the detected magnetic signal losses and subsequently inspected by the disc inspection instrument.

Claim 2

A method of selectively inspecting a magnetic disc in those locations where dropouts in the form of loss of magnetic signal intensity of information recorded thereon have been detected comprising the steps of: detecting dropouts on the disc by: rotating the disc at a substantially constant angular velocity while recording a magnetic signal of constant intensity along predefined concentric circular tracks rotating the disc at the same substantially constant angular velocity while reading the recorded magnetic signal along said predefined tracks comparing the intensity of the read signal with a predefined threshold to detect a level of loss of magnetic signal intensity rotating the disc at the same substantially constant angular velocity while reading the recorded magnetic signal along said predefined tracks comparing the intensity of the read signal with a different predefined threshold to detect another level of loss of magnetic signal intensity determining the angular position of detected losses of signal intensity by: measuring a first time interval between passage of a synchronizing signal on the disc and each detected loss of magnetic signal intensity measuring a second time interval between passage of said synchronizing signal and subsequent second passage of said synchronizing signal and dividing the first time interval by the second time interval and multiplyinq the resulting quotient by 360 to precisely define the angular position of each dropout in degrees storing information as to such detected losses of magnetic signal intensity in a computer, generating a map of the disc with the levels of losses of magnetic signal intensity color coded displaying said map on a color CRT display device and moving the disc into operative relationship with a disc inspecting instrument, and controlling the position of the disc with respect to such instrument on the basis of said detected signal loss location information stored in the computer, so that specific dropouts may be selected for inspection by positioning a cursor over the color coded symbol representing the detected magnetic signal losses and subsequently inspected by the disc inspection instrument.