What was found
AFTER TAKEOFF, PROP GAUGE FOR NR 1 ENGINE DROPPED TO 0 RPM AND REMAINED THERE FOR THE REMAINDER OF THE FLIGHT AND TAXI. MAINTENANCE R & R NR 1 ENGINE TACH GENERATOR. MAINTENANCE THEN INSTALLED A GASKET, TACH GEN, AND GROUND RAN NR 1 ENGINE WHICH OPERATIONALLY CHECKED GOOD.