As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOTH XPDR SYS FAILED AIR RETURN TO DENDUE TO INTL FLT TCAS FAULT DISPLAYED AT ENGINE START. REF TSM TASKS 34-43-00-810-820 AND 34-43-00-810-821-A, REF LMC LP 6055083 FOR GUIDANCE TO REPLACE TCAS COMPUTER. ACCOMPLISHED BITE TEST OF INSTALLED TCAS COMPUTER IAW AMM 34-43-00-740-001-A. TESTED GOOD. ALSO ACCOMPLISHED BITE TEST & OPERATIONAL TEST OF BOTH ATC ''S SYSTEMS , IAW AMM 34-52-00-740-004-A & AMM 34-52-00-710-003-A. BOTH ATC 1 & 2 TESTED GOOD . TCAS TRANSCEIVER RPL AS PER LP 6055083