As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSPECTION TYPE:N/A**ATB** - ON CLIMB OUT ABOVE 10,000 FEET THE AIRSPEED TAPE VMO/MMO (CHECKERED TAPE) WOULD NOT GO ABOVE 265KIAS. AFTER SPEAKIN WITH FLIGHT CONTROL AND AMC THE DECISION WAS MADE TO AIR TURN BACK.TOGGLED VMO SWITCH ACCOMPLISHED OPS CK PER AMM 34-12-00 OPS CK NORMAL COULD NOT DUPLICTE FAULT