The data gaps in CINRAD/SA radar image products are one of typical faults. Through the detail analysis of signal flow and movement locus of antenna with BDAVC5, it is found that the rotary transformer works abnormally because of low excitation voltage, which makes the radar directly skip to the next elevation scan without completing the current elevation scan. Such faults always occur along with the problems of the transmitter system or servo system, and induce the absence of radar data. Based on the findings, a serial of suggestions for different faults are proposed, and the software of BDAVC5 is useful for the fault location in servo system.