We used Xilinx FPGA to drive ADV7393 to output a PAL format video. Out of close 10 chips we buy, only 2 work properly with the output. We bought from different legit vendors and even try digikey. Once it work, the chip can output test pattern from FPGA and also form the internal pattern generators. But if it doesn't work, nothing is output. We measure the CLK and power. everything should be fine. Is it really possilble most of the cihps we bought are faulty?