Why is there a MAIN COIL SENSE FAIL during the internal frequency self calibration on the 8590 Series Spectrum Analyzer?

This failure occured while the main coil of the 1st LO or YTO was being calibrated. The firmware detected a linearity or tuning problem and was unable to set the calibrator output frequency to the correct screen location. The most probable cause is the A7 analog board, which controls all the tuning circuitry for the YTO.