As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED AT 15,000 FT, DOWN TO EMERGENCY POWER. LOSS OF POWER TO AC BUSS 1 AND DC BUSS 1. STARTED APU, WOULD NOT CONNECT TO AC BUSS 1. HAD MULTIPLE EICAS MESSAGES WITH "AVNX MAU 1B FAIL". AIRCRAFT DIVERTED. R & R BUSS TIE CONTACTOR (BTC) 1 IAW AMM 24-51-07. OPS CHECKED OK. R & R SPDA AC POWER MODULE AS PRECAUTIONARY IAW AMM 24-51-13.