As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ADF WOULD NOT POINT BELOW 500 HKZ DUE TO ELECTRICAL NOISE GENERATED BY ALTERNATOR SYSTEM. FOUND THIS TYPE UNIT CAUSED INTERFERENCE DUE TO SWITCHING FREQUENCY OF REGULATION SYSTEM. ELEIMINATED PROBLEM BY RETURNING ALTERNATOR CONTROL SYSTEM TO OLDER LOW FREQUENCY REGULATOR SYSTEM.