As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAD/BOS - FLT 6171 - DURING CRUISE AT 1540 HOURS ON 8-18-97, MADE AN UNSCHEDULED LANDING AT IAD DUE TO CAPTIAN'S SYMBOL GENERATOR FAILED. AIRCRAFT RETURNED TO GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND REMOVED AND REPLACED SYMBOL GENERATOR, OPS CHECK OK. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (X)