What was found
STANDBY ALTIMETER 500 FT DIFFERENCE FROM CAPTAIN'S AT FLIGHT LEVEL 390. 400 FT DIFFERENCE AT FLIGHT LEVEL 200 AND 60 FT DIFFERENCE ON THE GROUND. SUPPLEMENTAL DATA UPDATE CAUSE: 500 FT DIFFERENCE FROM CAPTAIN'S ALTIMETER AT FLIGHT LEVEL 390. CORRECTIVE ACTIONS: ERFORMED LEAK CHECK, REPLACED THE STBY. ALTIMETER, TESTED THE SYSTEM AT 10,000 FT. SHOP FINDINGS: DURING THE TEST, IT WAS NOTICED THAT THE VIBRATOR WAS NOISY AND THERE WAS SOME STICKING ON THE DESCENT. THE UNIT WAS IN TOLERANCE, VIBRATOR WAS REPLACED AND THE DRUM COUNTER CLEANED.