What was found
DURING CRUISE FLIGHT AT FL260, CHECK DU3 & 4 CAS ILLUMINATED. BEGAN TO LOOSE PRESSURIZATION, STARTED EMERGENCY DECENT, DURING DECENT RAN CHECKLIST FOR DU FAIL. NO RESET. MAU CHANNEL B CAS ILLUMINATED. RAN CHECKLIST, NO RESET, MAU CHANNEL B CIRCUIT BREAKER TRIPPED. DECLARED AN EMERGENCY AND DIVERTED, AND LANDED SAFELY WITHOUT FURTHER INCIDENT. THE MAU CHANNEL B POWER SUPPLY WAS FOUND TO BE AT FAULT. IT WAS REMOVED AND REPLACED IAW AMM 12-B-31-42-00-00A-902A-A, MAU OPERATIONAL TEST COMPLETED IAW 12-B-31-41-00-00A-903A-A NO DEFECTS NOTED.