HS-TDK TCAS and transponder mode C failed

Entering the flightdeck before flight ,we found that TCAS failed in both TA and RA mode. According to MEL, it told that we must de-activate it. I accepted flight without TCAS because no any rules dictated that we must have TCAS for out flight. After airborne, ATC couldn't see our altitude (C mode). I tried many things to rectify it but it was useless. We continued flight with assistance from ATC. So, both TCAS and Transponder mode C unserviceable.We operated flight with caution and continue look around all the time. After landing , the LAE found that RA1 was fault. The LAE reseat box but we found later that that action didn't rectify our snags.