What was found
FLT # 836 STI-EWR/ EWR -JFK DIVERTED. " AIRCRAFT N971JT OPERATING FLIGHT 836 STI - JFK DIVERTED TO EWR DUE TO STANDBY HORIZON ATTITUDE INDICATOR INOPERATIVE, SHOWING OUT OF ORDER ON THE ISIS DISPLAY. THE INTEGRATED STANDBY INSTRUMENT SYSTEM (ISIS) WAS REPLACED BY EWR TECHS AND OPS CHECKS WERE SUCCESSFUL. THE AIRCRAFT THEN CONTINUED TO JFK. THIS AIRCRAFT DOES NOT HAVE PREVIOUS REPORTS RELATED TO INTEGRATED STANDBY INSTRUMENT SYSTEM FAILURES WITHIN THE LAST 30 DAYS. (PILOT REPORT: STAND BY HORIZON ATTITUDE INOPERATIVE SHOWS OUT OF ORDER ON SCREEN.); REMOVED AND REPLACED ISIS ASSY IAW AMM 34-22-25 OPS CHK OK A/C OK FOR SVC."