As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, CREW REPORTED A SYS A FLIGHT CONTROL MASTER CAUTION. FLIGHT ATTENDANTS HEARD A LOUD POP FROM CTR OF ACFT. CREW FOLLOWED QRH & RETURNED TO FIELD AT CLT WITHOUT INCIDENT. MX REPLACED GEAR TRANSFER VLV CONTROL BOARD. OPERATIONS CHECKED GOOD IAW AMM 32-09-20-724-015. OPERATIONS CHECKED A & B FLIGHT CONTROL LOW PRESS IAW AMM 27-09-61-705-015, NO DEFECTS NOTED.