TDK TCAS FAIL DURING FLT

During flight, "TCAS FAIL" came on both EADI with both transponder systems now and then.Our responsible licensed aircraft engineer told me that after landing he did not find anything wrong after BITE TEST at the transponder box below and normal test at the ATC TRANSPONDER panel.Maybe the cause of this problem came from the ventilation was not enough inside the panel of transponder.So,he needed time to fix it seriously.I consulted with OP to get this snag fixed last night. don't know whether it is okay or not?