What was found
ALT NR 1 INFLIGHT, COULD NOT RESET, AMMETER FOR ALT NR 1 SHOWED NORMAL CHARGE SOMETIME AND 0 CHARGE OTHER TIMES. ALT NR 2 SHOWED + 100 THEN -100 AFTER NR 1 SHUTOFF. BOTH WARNING LIGHTS CAME ON. AFTER LANDING, SHUT ENGINE COMPLETELY, RESTARTED FOR GROUND RUN UP SHOWED ALT NR1 ON, BUSS VOLT BELOW 28 VOLTS FOR 1 AND 2, AMP METER +50 FOR ALT 1 AND +100 ON ALT 2. SUSPECTED MOISTURE IN THE MCU. AFTER 4 HOURS, RETURNED TO AIRCRAFT, STARTED ENGINE AND ALL OPERATIONAL CHECKED NORMAL.