As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRPLANE DEPRESSURIZED AT 6000FT AGL IN "AUTO", VALVE FULL OPEN. WENT TO "STANDBY", PRESSURIZED MOMENTARILY THEN DEPRESSURIZED AGAIN IN "STANDBY", VALVE FULL OPEN. OK IN "MANUAL AC". FOUND VOLTAGE MISMATCH INSIDE THE AUTO PRESSURE CONTROLLER. REPLACED THE AUTO PRESSURE CONTROLLER AND ADC AND NR 1 DIGITAL AIR DATA COMPUTER. NO REPEATS SINCE ORIGINAL.