What was found
(CAN) AFTER LANDING, WHEN MOVING THE PROPELLER TO DISC, ONE ENGINE STAYED AT A HIGHER RPM FOR 2 TO 3 SECONDS WHILE THE OTHER ENGINE RPM DROPPED. THE CONSEQUENCE OF THESE DIFFERENCES RESULTED IN A HIGH YAW IN THE AIRCRAFT AND THE AIRCRAFT TURNED OFF THE RUNWAY. NO DAMAGE TO THE AIRCRAFT OR ENGINES IN THE INCIDENT, DURING TROUBLESHOOTING, ONE OF THE BETA BACK-UP SWITCHES IN THE CONTROLS WAS UNSERVICEABLE. RETURNED TO NORMAL WHEN THE SWITCH WAS REPLACED.