What was found
REINSTALLED ADC AFTER MOD STATUS UPGRADE AND CERTIFICATION. WHILE COMPLYING WITH CFR SECTION 91.411/91.413 FUNCTION TEST, NOTED NR 2 TRANSPONDER ALTITUDE READ-OUT WAS INVALID FROM 500 FEET TO 1,000 FEET AND AT EACH ASCENDING 500 FOOT INCREMENT TO THE NEXT THOUSAND. IN DESCENDING ALTITUDE TESTS, THE NR 2 TRANSPONDER READ INVALID FROM EACH 1,000 FOOT ALTITUDE READING THROUGH EACH 500 FOOT ALTITUDE LEVEL. REMOVED AND REPLACED TRANSPONDER AND REQUESTED SHOP BENCH REPORT ON FINDINGS.