What was found
UPON GEAR RETRACTION POST TAKEOFF, THE NLG FAILED TO RETRACT IN A TIMELY FASHION. THE NLG WAS PHYSICALLY DOWN, AND WE RECEIVED AN ADC SSEC MISCOMPARE EICAS MSG. AFTER APPROX 10-12 SECONDS THE NLG THEN RETRACTED AND BOTH THE EICAS MSG EXTINGUISHED WITH THE GEAR INDICATION GOING TO UP & NORMAL LOCKED/DOOR CLOSED. BOTH L/R MLG FUNCTIONED NORMALLY UNAFFECTED. UPON EXTENSION AT THE DESTINATION THE GEAR EXTENDED WITH A LOUD THUNK BUT THE FUNCTION WAS NORMAL SHOWING DOWN AND LOCKED GREEN. FUNCTION WAS NORMIAL DOWN & LOCKED. R & R HYD RETURN CHK VALVE & INSTALLED SUPPLIED, NEW HYD RETURN CHK VALVE. WORK DONE IAW AMM 32-30-25. PERFORMED LANDING GEAR OPS CHK MULTIPLE TIMES. OPS CHKD GOOD. WORK DONE IAW AMM 32-00-00.