What was found
DURING AVIONICS CONFIGURATION OF THE RUN-UP PROCEDURES, WITH ENGINES AT IDLE, THE MAST MOMENT INDICATOR DRIFTED OFF THE CIRCULAR SCALE 2 TIMES AND THEN THE CIRCULAR SCALE DISAPPEARED COMPLETELY, IMMEDIATELY NOTIFIED MAINTENANCE, THE AIRCRAFT WAS SHUT DOWN, THE AIRCRAFT TI REVIEWED THE MAINTENANCE PAGE AND THE MM RECORDED MM> THAN 64% FOR 2.8 SEC WITH A MAX READING OF 111.1. REMOVED AND REPLACED SSTU IAW 63-42-00, 4-2; COMPLETED FUNCTIONAL TEST IAW 63-42-00, 5-1.