Method of self-testing magneto-resistive heads for instability in a disk drive

Abstract

An MR head self-testing method is provided to test for instability in MR heads incorporated with a hard disk drive. A first method is carried out with the disk rotating and includes positioning the MR head over a rotating magnetic storage disk and controlling the MR head to read from erased data fields defined on the disk. This read signal is filtered and conditioned according to preprogrammed filter coefficients contained in an FIR filter to provide an exaggerated read error signal. The exaggerated read error signal is provided to a digital comparator and counter circuit for detecting and counting voltage baseline jumps that exceed preprogrammed positive and/or negative threshold values. The counted positive and negative voltage baseline jumps, which are indicative of MR head instability, are provided to an error diagnostic register for analysis. If the error diagnostic register contains single polarity voltage baseline jumps, the voltage baseline jumps may be caused by thermal asperities on the disk. If the error diagnostic register contains both positive and negative voltage baseline jumps, the voltage baseline jumps may be caused by MR head instability. A second method is carried out with the disk stationary so there is no opportunity for thermal asperities to generate baseline jumps. Possible instabilities can only be of the Barkhausen noise or dielectric breakdown types.