As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, BOTH ATC TRANSPONDERS INOP. THE CREW RETURNED TO DEPARTURE WITHOUT FURTHER INCIDENT. MX REPLACED TCAS/ATC CONTROL PANEL AND TIGHTENED CONNECTOR ON TRANSPONDER ANTENNA SWITCHING RELAY. OPS CHECK GOOD IAW MM 34-53-0. ACFT WAS RETURNED TO SERVICE.